{"gene":"MYBPC3","run_date":"2026-04-29T11:37:56","timeline":{"discoveries":[{"year":1999,"finding":"The MyBP-C motif (N-terminal regulatory domain of cardiac MyBP-C) binds to the N-terminal 126 residues of the myosin S2 segment; two FHC-causing mutations in beta-myosin S2 (R870H and E924K) drastically reduce or abolish this binding, suggesting cMyBP-C regulates contraction through this S2 interaction.","method":"In vitro binding assay (Kd measurements), fragment localization in cardiomyocytes and isolated myofibrils","journal":"Journal of molecular biology","confidence":"High","confidence_rationale":"Tier 1 — in vitro binding with quantitative Kd measurements plus functional localization, replicated concept across multiple FHC mutations","pmids":["10024460"],"is_preprint":false},{"year":2008,"finding":"PKA-mediated phosphorylation of cMyBP-C relieves a tether-like constraint on myosin heads, increasing their proximity to actin (azimuthal/radial displacement toward thin filaments) as measured by increased equatorial intensity ratio I(11)/I(10) in wild-type but not cMyBP-C null myocardium; cMyBP-C also stabilizes the myofilament lattice spacing.","method":"Synchrotron low-angle X-ray diffraction of skinned trabeculae from wild-type and cMyBP-C null mice with/without PKA treatment","journal":"Circulation research","confidence":"High","confidence_rationale":"Tier 1 — direct structural measurement with rigorous null-mouse controls demonstrating cMyBP-C dependence","pmids":["18599866"],"is_preprint":false},{"year":2009,"finding":"MYBPC3 truncation and missense mutations cause haploinsufficiency: no truncated cMyBP-C protein is detectable in human myectomy tissue, and total myofibrillar cMyBP-C levels are significantly reduced (~76% of control) in MYBPC3-mutant HCM patients.","method":"Immunoblotting and RT-PCR of human myectomy samples vs. donor hearts","journal":"Circulation research","confidence":"High","confidence_rationale":"Tier 2 — orthogonal protein and mRNA quantification in human tissue, multiple mutation types tested","pmids":["19574547"],"is_preprint":false},{"year":2004,"finding":"Heterozygous cMyBP-C null mice (one functional Mybpc3 allele) develop asymmetric septal hypertrophy with fibrosis, while homozygous null mice develop eccentric LV hypertrophy with impaired relaxation; establishing that partial cMyBP-C deficiency is sufficient to cause a key HCM phenotypic feature.","method":"Targeted deletion of exons 1–2 in mice; molecular, functional (echocardiography), and morphological analyses at multiple ages","journal":"Cardiovascular research","confidence":"High","confidence_rationale":"Tier 2 — clean genetic KO with dose-dependent phenotype across heterozygous and homozygous animals, multiple readouts","pmids":["15249187"],"is_preprint":false},{"year":2011,"finding":"N-terminal cMyBP-C fragments bind to F-actin subdomain 1, with density extending tangentially toward actin's pointed end; this binding position could modulate tropomyosin position and interfere with myosin head binding to actin.","method":"Negative stain electron microscopy and 3D helical reconstruction of F-actin decorated with bacterially expressed N-terminal cMyBP-C fragments; atomic model fitting","journal":"Journal of molecular biology","confidence":"High","confidence_rationale":"Tier 1 — structural determination with 3D reconstruction and molecular fitting","pmids":["21601575"],"is_preprint":false},{"year":2012,"finding":"In Mybpc3 knock-in HCM mice, even before left ventricular hypertrophy develops, heterozygous mice exhibit increased myofilament Ca2+ sensitivity and diastolic dysfunction, indicating these are primary consequences of Mybpc3 mutation independent of hypertrophy.","method":"Skinned ventricular trabeculae force measurements, intact myocyte Ca2+ transients, echocardiography/Doppler in heterozygous and homozygous knock-in mice","journal":"Journal of molecular and cellular cardiology","confidence":"High","confidence_rationale":"Tier 2 — multiple orthogonal functional methods in well-characterized knock-in model with pre-hypertrophic time point","pmids":["22465693"],"is_preprint":false},{"year":2011,"finding":"Mybpc3-targeted knock-in mice show altered ubiquitin-proteasome system (UPS) and autophagy-lysosome pathway (ALP): early postnatal UPS activation, specific UPS impairment in old knock-in (but not knock-out) mice expressing truncated cMyBP-C, and defective ALP-mediated degradation in both models, implicating proteolytic dysfunction in HCM pathogenesis.","method":"Ub(G76V)-GFP reporter mouse crosses, proteasomal activity assays, ALP marker quantification in KI and KO mice","journal":"Basic research in cardiology","confidence":"Medium","confidence_rationale":"Tier 2 — reporter mouse assay with KI vs. KO comparison, but mechanism not fully reconstituted","pmids":["22189562"],"is_preprint":false},{"year":2013,"finding":"The HCM-causing E258K missense mutation in cMyBP-C abolishes interaction between the N-terminal cMyBP-C and myosin S2 (assessed by yeast two-hybrid) and increases affinity for actin, causing accelerated contractile kinetics and severely reduced twitch force in engineered cardiac tissue.","method":"Adenoviral gene transfer in cMyBP-C null murine engineered cardiac tissue; yeast two-hybrid; force measurements; phosphorylation analysis","journal":"The Journal of general physiology","confidence":"High","confidence_rationale":"Tier 1–2 — multiple orthogonal methods (yeast two-hybrid, functional reconstitution in tissue model, phosphorylation analysis) in single study","pmids":["23980194"],"is_preprint":false},{"year":2015,"finding":"The South Asian MYBPC3 25-bp deletion mutation produces a C10 domain variant (cMyBP-CC10mut) that fails to localize to the C-zone of the sarcomere, cannot interact with myosin LMM, resides predominantly in the soluble fraction, and causes reduced fractional shortening and sarcomere relaxation without affecting Ca2+ transients.","method":"Adenoviral expression in adult rat cardiomyocytes; immunofluorescence; subcellular fractionation; co-sedimentation and protein cross-linking assays; protein homology modeling","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 1–2 — multiple orthogonal biochemical and cell biology methods establishing mechanism","pmids":["25583989"],"is_preprint":false},{"year":2015,"finding":"The HCM-associated L348P mutation in the M-domain of cMyBP-C causes a gain-of-function by shifting tropomyosin to approximately the open position on thin filaments (larger than the closed-position shift caused by wild-type), enhancing Ca2+-sensitization in a phosphorylation-independent manner.","method":"Electron microscopy and 3D reconstruction of thin filaments decorated with L348P-mutant vs. wild-type and phosphorylated N-terminal cMyBP-C fragments","journal":"Journal of molecular and cellular cardiology","confidence":"High","confidence_rationale":"Tier 1 — structural 3D reconstruction with direct comparison of WT, phosphorylated, and mutant fragments","pmids":["26718724"],"is_preprint":false},{"year":2019,"finding":"Stepwise depletion of cMyBP-C causes reciprocal augmentation of myosin contractility; cMyBP-C depletion enhances the myosin state enabling ATP hydrolysis and thin filament interactions while reducing the super-relaxed (energy-conserving) conformation; the myosin ATPase inhibitor MYK-461 rescues relaxation deficits caused by MYBPC3 mutations.","method":"Genetic and biochemical approaches in mouse and human cardiomyocytes with MYBPC3 mutations; myosin conformation assays; pharmacological rescue with MYK-461","journal":"Science translational medicine","confidence":"High","confidence_rationale":"Tier 1–2 — multiple orthogonal genetic/biochemical methods, pharmacological rescue in two cell systems","pmids":["30674652"],"is_preprint":false},{"year":2019,"finding":"MYBPC3 premature termination codon mutations chronically activate the nonsense-mediated decay (NMD) pathway, leading to aberrant calcium handling (prolonged decay kinetics, elevated diastolic Ca2+) in iPSC-CMs; specific NMD inhibition reverses the molecular phenotype and normalizes calcium handling.","method":"Isogenic iPSC-CMs from HCM patients; comprehensive phenotypic and transcriptome analyses; pharmacological NMD inhibition","journal":"Circulation","confidence":"High","confidence_rationale":"Tier 2 — isogenic system with pharmacological rescue providing direct mechanistic link between NMD activation and Ca2+ phenotype","pmids":["30586709"],"is_preprint":false},{"year":2012,"finding":"Protein kinase D (PKD) binds to cMyBP-C in contracting cardiomyocytes and phosphorylates it at Ser315; PKD-mediated phosphorylation of cMyBP-C increases maximal Ca2+-activated tension (Tmax) in wild-type but not cMyBP-C KO skinned myocytes, establishing cMyBP-C as essential for PKD's effect on Tmax.","method":"Immunoprecipitation; permeabilized ventricular myocytes from WT and cMyBP-C KO mice incubated with active PKD; force measurements","journal":"American journal of physiology. Heart and circulatory physiology","confidence":"High","confidence_rationale":"Tier 1–2 — Co-IP establishing binding, KO rescue experiment establishing functional requirement","pmids":["22636676"],"is_preprint":false},{"year":2014,"finding":"Site-specific phosphorylation of cMyBP-C differentially affects contractile mechanisms: the DAD phosphomimetic (Asp273-Ala282-Asp302) significantly decreases isometric tension, stiffness, and cross-bridge kinetics (2πc), while SAS and ADA variants cause minimal changes, demonstrating that Ser282 in its non-phosphorylated state combined with phosphomimetic residues at 273/302 is detrimental.","method":"Sinusoidal analysis in papillary/trabecular fibers from cMyBP-C null mice expressing site-specific phosphorylation mutant transgenes (ADA, DAD, SAS) vs. WT","journal":"Biophysical journal","confidence":"High","confidence_rationale":"Tier 1 — in vitro reconstitution with specific phosphosite mutations and rigorous mechanical analysis","pmids":["24606935"],"is_preprint":false},{"year":2020,"finding":"Acute removal of cMyBP-C N-terminal domains (C0–C7) from sarcomeres in situ reduces myofilament Ca2+ sensitivity, increases cross-bridge cycling rate (ktr), and induces spontaneous oscillatory contractions (SPOC) at submaximal Ca2+; ligation of recombinant C0-C7 rescues pCa50 and ktr and abolishes oscillations, while phosphorylated C0-C7 is less effective, revealing a novel role for cMyBP-C N-terminal domains in damping sarcomere-driven contractile waves.","method":"Novel 'cut and paste' approach using TEVp cleavage and SpyCatcher/SpyTag system in detergent-permeabilized cardiomyocytes from gene-edited Spy-C mice; force measurements","journal":"Circulation research","confidence":"High","confidence_rationale":"Tier 1 — reconstitution with acute domain removal and re-ligation, functional rescue with phosphorylation variant comparison","pmids":["32078438"],"is_preprint":false},{"year":2006,"finding":"cMyBP-C is required for normal in vivo LV function: cMyBP-C null mice show compromised systolic and diastolic function, and lack the contractile improvement normally seen with beta-adrenergic stimulation or pressure overload adaptation, indicating cMyBP-C is necessary for adrenergic-mediated enhancement of contractility.","method":"Pressure-volume relations and echocardiography in cMyBP-C null vs. wild-type mice; beta-adrenergic stimulation; aortic banding","journal":"American journal of physiology. Heart and circulatory physiology","confidence":"High","confidence_rationale":"Tier 2 — clean genetic null with multiple in vivo readouts and pharmacological challenge","pmids":["17122190"],"is_preprint":false},{"year":2020,"finding":"Heterozygous MYBPC3 frameshift mutations cause allelic loss of function (reduced WT mRNA) but MyBP-C protein levels are maintained through reduced degradation rate (not increased synthesis), indicating cardiomyocytes have an innate protein-level compensatory mechanism for MyBP-C stoichiometry.","method":"Patient and genome-engineered iPSC-CMs; stable isotope labeling to measure synthesis and degradation rates; RNA-Seq; contractile function assays","journal":"JCI insight","confidence":"High","confidence_rationale":"Tier 2 — stable isotope pulse-chase directly measuring synthesis/degradation rates with isogenic controls","pmids":["31877118"],"is_preprint":false},{"year":2020,"finding":"Nontruncating MYBPC3 pathogenic missense variants cluster in domains C3, C6, and C10; C10 domain missense variants fail to incorporate into myofilaments and have ~90% accelerated degradation rates, while C3 and C6 variants incorporate normally with similar degradation to wild-type, revealing domain-specific loss-of-function mechanisms.","method":"Expression of mutant MyBP-C in rat ventricular myocytes; immunofluorescence for myofilament localization; degradation rate measurements","journal":"Circulation. Genomic and precision medicine","confidence":"High","confidence_rationale":"Tier 2 — direct cell-based localization and degradation assays across multiple pathogenic variants","pmids":["32841044"],"is_preprint":false},{"year":2016,"finding":"In Mybpc3 knock-in HCM mice, beta-adrenergic stimulation causes preferential PKA phosphorylation of phospholamban (PLN) over cardiac troponin I (cTnI), resulting in impaired myofilament contractile and lusitropic response despite maintained Ca2+ handling response.","method":"Permeabilized and intact cardiomyocytes from HET and KI Mybpc3 knock-in mice; phosphorylation state measurements; sarcomere length and force measurements; isoprenaline stimulation","journal":"Cardiovascular research","confidence":"Medium","confidence_rationale":"Tier 2 — direct phosphorylation measurements in knock-in cardiomyocytes, single lab","pmids":["26825555"],"is_preprint":false},{"year":2017,"finding":"Autophagy is impaired in Mybpc3 knock-in HCM mice (blunted autophagic flux, residual body and glycogen accumulation, increased Akt-mTORC1 signaling); rapamycin treatment or caloric restriction restores autophagic flux and partially rescues cardiomyopathy, establishing impaired autophagy as a pathomechanism in MYBPC3-mutant HCM.","method":"LC3-II protein levels, autophagic flux assay, Akt-mTORC1 signaling in KI mice and human HCM myectomies; rapamycin treatment; caloric restriction","journal":"Circulation. Heart failure","confidence":"Medium","confidence_rationale":"Tier 2 — multiple markers plus pharmacological rescue, but mechanism linking cMyBP-C to mTORC1 not fully reconstituted","pmids":["29021349"],"is_preprint":false},{"year":2022,"finding":"MYBPC3 is expressed in cardiac fibroblasts (not only cardiomyocytes); CRISPR-mediated Mybpc3 disruption in fibroblasts activates NF-κB signaling, upregulates TGF-β1 and HIF-1α, enhances aerobic glycolysis, and accelerates fibroblast activation, contributing to myocardial fibrosis in HCM.","method":"CRISPR KO of Mybpc3 in NIH3T3 and cardiac fibroblasts; NF-κB signaling assays; TGF-β1, HIF-1α, glycolysis marker quantification; R495Q mutant pig model","journal":"Cell death & disease","confidence":"Medium","confidence_rationale":"Tier 2 — multiple pathway assays in cell-based KO system plus in vivo pig model, but novel finding not yet replicated","pmids":["36357371"],"is_preprint":false},{"year":2021,"finding":"Among nontruncating MYBPC3 variants, approximately half of HCM-linked variants show alterations in RNA splicing or protein stability, both leading to cMyBP-C haploinsufficiency; these protein haploinsufficiency drivers associate with HCM pathogenicity with 100% and 94% specificity respectively.","method":"Minigene splicing assay; protein stability assays for 44 nontruncating MYBPC3 variants classified by cosegregation and population genetics","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 2 — systematic cell-based functional testing of 44 variants with orthogonal splicing and stability assays","pmids":["34097875"],"is_preprint":false},{"year":2013,"finding":"AAV-mediated 5'-trans-splicing of Mybpc3 pre-mRNA in vivo produces full-length repaired cMyBP-C protein that incorporates correctly into the sarcomere; repaired mRNA reached up to 66% of total Mybpc3 transcripts in cultured cardiac myocytes.","method":"AAV-delivered pre-trans-splicing molecules in cultured cardiac myocytes and mouse hearts; immunoprecipitation; immunofluorescence for sarcomere incorporation","journal":"Molecular therapy. Nucleic acids","confidence":"Medium","confidence_rationale":"Tier 2 — protein detection and sarcomere localization confirmed by immunoprecipitation and imaging","pmids":["23820890"],"is_preprint":false},{"year":2014,"finding":"Heterozygous MYBPC3 truncation mutation mice subjected to pressure overload (TAC) show haploinsufficiency (significantly reduced cMyBP-C at 4 weeks post-TAC), impaired force generation, higher Ca2+ sensitivity, blunted length-dependent activation, and greater hypertrophy than WT-TAC, establishing that stress-induced haploinsufficiency exacerbates dysfunction.","method":"Transverse aortic constriction in HET MYBPC3 truncation mice; myofilament force measurements; Ca2+ sensitivity; echocardiography; RNA sequencing","journal":"Journal of molecular and cellular cardiology","confidence":"High","confidence_rationale":"Tier 2 — in vivo stress model with myofilament functional readouts and protein quantification","pmids":["25463273"],"is_preprint":false}],"current_model":"cMyBP-C (encoded by MYBPC3) is a thick filament-associated regulatory protein that constrains myosin head proximity to actin through its N-terminal domains binding myosin S2; PKA and other kinases (CaMKII, PKC, PKD) phosphorylate specific serine residues (Ser273, Ser282, Ser302, Ser315) to relieve this constraint, increase cross-bridge cycling kinetics, and augment Ca2+-activated tension; the N-terminal domains also bind actin and shift tropomyosin position to modulate thin filament activation and damp spontaneous contractile oscillations; the C-terminal C10 domain anchors cMyBP-C to the myosin rod (LMM), and most HCM-causing truncating MYBPC3 mutations lead to NMD-mediated mRNA degradation and protein haploinsufficiency (reduced full-length cMyBP-C in myofilaments), which reciprocally augments myosin ATPase activity and reduces the super-relaxed myosin state, causing hypercontractility and impaired relaxation characteristic of HCM."},"narrative":{"teleology":[{"year":1999,"claim":"Establishing the primary molecular interaction: the N-terminal regulatory domain of cMyBP-C binds the myosin S2 segment, and HCM mutations in S2 disrupt this interaction, providing the first direct biochemical basis for cMyBP-C's contractile regulatory function.","evidence":"In vitro binding assays with Kd measurements using recombinant cMyBP-C motif and myosin S2 fragments, plus localization in cardiomyocytes","pmids":["10024460"],"confidence":"High","gaps":["Whether the S2 interaction is the sole or primary mechanism of cross-bridge regulation was unclear","In vivo relevance of the binding affinity not yet tested","Phosphorylation effects on this interaction not assessed"]},{"year":2004,"claim":"Genetic proof that cMyBP-C dose determines cardiac phenotype: heterozygous Mybpc3 knockout mice develop asymmetric septal hypertrophy resembling human HCM, while homozygous nulls show eccentric hypertrophy with diastolic dysfunction, establishing haploinsufficiency as sufficient for disease.","evidence":"Targeted deletion of Mybpc3 exons 1–2 in mice with echocardiographic, molecular, and morphological analysis at multiple ages","pmids":["15249187"],"confidence":"High","gaps":["Whether human MYBPC3 mutations act purely through haploinsufficiency or also via poison-peptide effects was not resolved","Mechanism linking reduced cMyBP-C to hypertrophic signaling not identified"]},{"year":2006,"claim":"cMyBP-C is required for normal in vivo contractile reserve: null mice lack the contractile enhancement normally elicited by β-adrenergic stimulation, showing cMyBP-C is essential for the adrenergic-mediated augmentation of cardiac function.","evidence":"Pressure-volume analysis and echocardiography in cMyBP-C null versus wild-type mice with β-adrenergic challenge and aortic banding","pmids":["17122190"],"confidence":"High","gaps":["Whether the deficit reflects loss of cMyBP-C phosphorylation specifically or a general structural disruption was unresolved","Molecular basis of the blunted adrenergic response not dissected"]},{"year":2008,"claim":"Structural evidence for the tether model: PKA phosphorylation of cMyBP-C displaces myosin heads radially toward actin, and this displacement is entirely absent in cMyBP-C null myocardium, directly demonstrating that cMyBP-C constrains myosin head position in a phosphorylation-dependent manner.","evidence":"Synchrotron low-angle X-ray diffraction of skinned trabeculae from wild-type and cMyBP-C null mice ± PKA","pmids":["18599866"],"confidence":"High","gaps":["Which phosphosites mediate the tether release was not resolved","Contribution of thin-filament binding to the structural rearrangement not assessed"]},{"year":2009,"claim":"Direct confirmation of haploinsufficiency in human HCM: no truncated cMyBP-C protein is detectable in myectomy tissue from patients with MYBPC3 truncation mutations, and total cMyBP-C is reduced to ~76% of normal, establishing that truncated transcripts are degraded rather than producing poison peptides.","evidence":"Immunoblotting and RT-PCR of human myectomy samples versus donor hearts across multiple MYBPC3 mutation types","pmids":["19574547"],"confidence":"High","gaps":["Whether the residual ~76% protein level is sufficient to prevent disease or represents an incomplete compensatory mechanism was unknown","Mechanism of mRNA degradation (NMD) not directly demonstrated in these samples"]},{"year":2011,"claim":"Dual binding target identified: cMyBP-C N-terminal domains bind F-actin subdomain 1, positioning them to shift tropomyosin and modulate thin-filament activation, revealing a second regulatory interface beyond myosin S2.","evidence":"Negative-stain EM and 3D helical reconstruction of F-actin decorated with N-terminal cMyBP-C fragments","pmids":["21601575"],"confidence":"High","gaps":["Functional consequence of actin binding on thin-filament activation kinetics not directly measured","Relative contributions of actin versus S2 binding to contractile regulation unclear"]},{"year":2012,"claim":"Increased myofilament Ca²⁺ sensitivity and diastolic dysfunction are primary consequences of MYBPC3 mutation, preceding and independent of hypertrophy, reframing these as initiating events rather than secondary consequences.","evidence":"Skinned trabeculae force measurements, intact myocyte Ca²⁺ transients, and echocardiography in pre-hypertrophic heterozygous and homozygous Mybpc3 knock-in mice","pmids":["22465693"],"confidence":"High","gaps":["Whether correcting Ca²⁺ sensitivity alone would prevent subsequent hypertrophy was not tested","Specific molecular mechanism by which mutant cMyBP-C increases Ca²⁺ sensitivity not identified"]},{"year":2012,"claim":"PKD phosphorylates cMyBP-C at Ser315 and requires cMyBP-C to augment maximal Ca²⁺-activated tension, expanding the kinase repertoire regulating cMyBP-C beyond PKA/CaMKII.","evidence":"Co-immunoprecipitation in contracting cardiomyocytes; force measurements in permeabilized WT versus cMyBP-C KO myocytes incubated with active PKD","pmids":["22636676"],"confidence":"High","gaps":["Physiological stimulus triggering PKD-cMyBP-C signaling in vivo not established","Whether PKD phosphorylation of Ser315 alone is sufficient or requires cooperative phosphorylation at other sites"]},{"year":2013,"claim":"The E258K missense mutation reveals how gain-of-function at the thin filament and loss-of-function at the thick filament converge: abolishing S2 interaction while increasing actin affinity accelerates contractile kinetics and reduces force, mechanistically linking HCM missense mutations to altered dual-binding properties.","evidence":"Yeast two-hybrid for S2 binding; force measurements in engineered cardiac tissue from cMyBP-C null mice reconstituted with WT or E258K cMyBP-C","pmids":["23980194"],"confidence":"High","gaps":["Whether other missense mutations show the same dual-binding alteration pattern was untested","In vivo hemodynamic consequences not assessed"]},{"year":2014,"claim":"Phosphosite hierarchy established: Ser282 non-phosphorylation combined with phosphomimetic substitutions at Ser273/302 (DAD variant) is detrimental, significantly reducing isometric tension and cross-bridge kinetics, demonstrating that site-specific phosphorylation patterns have opposing functional outcomes.","evidence":"Sinusoidal analysis in papillary fibers from cMyBP-C null mice expressing transgenic phosphosite-specific mutants (ADA, DAD, SAS)","pmids":["24606935"],"confidence":"High","gaps":["Whether this phosphorylation hierarchy exists in vivo under physiological signaling conditions was not demonstrated","No structural explanation for why Ser282 state determines the functional outcome"]},{"year":2015,"claim":"C10 domain integrity is essential for sarcomeric anchoring: the South Asian 25-bp deletion produces a C10 variant that cannot bind myosin LMM, fails to incorporate into sarcomeres, and causes contractile dysfunction, identifying a founder mutation mechanism.","evidence":"Adenoviral expression in adult rat cardiomyocytes; co-sedimentation, cross-linking, immunofluorescence, and subcellular fractionation","pmids":["25583989"],"confidence":"High","gaps":["Whether soluble mislocalized cMyBP-C has toxic gain-of-function effects was not addressed","In vivo phenotype of this specific mutation in animal models not established"]},{"year":2015,"claim":"HCM missense mutation L348P shifts tropomyosin to the open position on thin filaments beyond the effect of wild-type cMyBP-C, providing structural evidence that thin-filament activation by N-terminal domains is a gain-of-function mechanism in HCM.","evidence":"EM 3D reconstruction of thin filaments decorated with L348P versus WT and phosphorylated N-terminal cMyBP-C fragments","pmids":["26718724"],"confidence":"High","gaps":["Whether tropomyosin shift alone accounts for the Ca²⁺ sensitization phenotype not tested in intact sarcomeres","How phosphorylation modulates the L348P gain-of-function not determined"]},{"year":2019,"claim":"The unifying biophysical mechanism: cMyBP-C depletion shifts myosin from the super-relaxed (energy-conserving) state to a disordered-relaxed (ATP-hydrolyzing) state, and the myosin ATPase inhibitor MYK-461 rescues relaxation deficits, providing a pharmacological strategy targeting the downstream consequence of haploinsufficiency.","evidence":"Genetic and biochemical myosin conformation assays in mouse and human MYBPC3-mutant cardiomyocytes; pharmacological rescue with MYK-461","pmids":["30674652"],"confidence":"High","gaps":["Whether super-relaxed state reduction is the sole driver of hypercontractility or whether thin-filament effects contribute independently remains unresolved","Long-term efficacy and safety of MYK-461 in MYBPC3 mutation carriers not established"]},{"year":2019,"claim":"NMD as chronic stressor: premature termination codon mutations constitutively activate nonsense-mediated decay, and this chronic NMD activation—rather than haploinsufficiency alone—causes aberrant calcium handling; NMD inhibition normalizes calcium transients, revealing a non-sarcomeric pathogenic pathway.","evidence":"Isogenic iPSC-CMs from HCM patients; transcriptome analysis; pharmacological NMD inhibition with phenotype rescue","pmids":["30586709"],"confidence":"High","gaps":["Mechanism by which chronic NMD activation leads to calcium handling defects not identified","Whether NMD inhibition is therapeutically viable in vivo unknown"]},{"year":2020,"claim":"Acute reconstitution proves the N-terminal domains maintain sarcomeric stability: removal of C0–C7 from sarcomeres reduces Ca²⁺ sensitivity, speeds cross-bridge cycling, and triggers spontaneous oscillatory contractions; re-ligation rescues all phenotypes, establishing that cMyBP-C N-terminal domains actively damp contractile instability.","evidence":"TEVp cleavage and SpyCatcher/SpyTag re-ligation of N-terminal domains in permeabilized cardiomyocytes from gene-edited mice","pmids":["32078438"],"confidence":"High","gaps":["Whether SPOC occurs in intact myocardium with partial cMyBP-C depletion not tested","The structural basis by which N-terminal domains suppress oscillations is unknown"]},{"year":2020,"claim":"Protein-level compensation: heterozygous MYBPC3 frameshift mutations reduce WT mRNA but cardiomyocytes maintain near-normal cMyBP-C protein levels by decreasing degradation rate, revealing an innate post-translational buffering mechanism.","evidence":"Stable isotope labeling (SILAC) in patient and genome-engineered iPSC-CMs measuring synthesis and degradation rates","pmids":["31877118"],"confidence":"High","gaps":["Whether this compensatory mechanism fails under hemodynamic stress to produce haploinsufficiency in vivo is not resolved","Molecular sensor/pathway controlling degradation rate adjustment unknown"]},{"year":2020,"claim":"Domain-specific variant pathomechanisms: C10 missense variants fail to incorporate into myofilaments and degrade ~90% faster, while C3/C6 variants incorporate normally, demonstrating that nontruncating mutations cause loss-of-function through distinct domain-dependent mechanisms.","evidence":"Immunofluorescence and degradation rate measurements for mutant MyBP-C expressed in rat ventricular myocytes","pmids":["32841044"],"confidence":"High","gaps":["Functional consequence of incorporated C3/C6 variants on contractility not measured","Whether C3/C6 variants that incorporate normally act through altered binding affinities not tested"]},{"year":2021,"claim":"Systematic classification of nontruncating variants: ~50% of pathogenic missense/in-frame variants cause haploinsufficiency via RNA splicing defects or protein instability, with high specificity for pathogenicity, providing a functional framework for variant interpretation.","evidence":"Minigene splicing assays and protein stability assays for 44 nontruncating MYBPC3 variants correlated with cosegregation and population data","pmids":["34097875"],"confidence":"High","gaps":["The other ~50% of pathogenic nontruncating variants presumably act through altered function rather than haploinsufficiency, but their mechanisms are uncharacterized","Whether splicing and stability assays are sufficient for clinical variant classification not validated prospectively"]},{"year":null,"claim":"Key unresolved questions: (1) the structural basis of the cMyBP-C N-terminal interaction with both myosin S2 and actin simultaneously, and how phosphorylation switches between these binding modes at atomic resolution; (2) the molecular sensor that adjusts cMyBP-C degradation rate to compensate for haploinsufficiency; (3) whether thin-filament and thick-filament regulatory mechanisms of cMyBP-C are independently sufficient for disease or must converge; (4) the non-sarcomeric role of MYBPC3 in cardiac fibroblasts and its contribution to fibrosis in HCM.","evidence":"","pmids":[],"confidence":"Low","gaps":["No high-resolution structure of cMyBP-C N-terminal domains bound simultaneously to S2 and actin in the sarcomeric context","Post-translational compensation pathway linking mRNA haploinsufficiency to reduced protein degradation unidentified","Fibroblast role described in single study requiring independent replication"]}],"mechanism_profile":{"molecular_activity":[{"term_id":"GO:0008092","term_label":"cytoskeletal protein binding","supporting_discovery_ids":[0,4,7,14]},{"term_id":"GO:0005198","term_label":"structural molecule activity","supporting_discovery_ids":[1,8,14]},{"term_id":"GO:0098772","term_label":"molecular function regulator activity","supporting_discovery_ids":[1,10,14]}],"localization":[{"term_id":"GO:0005856","term_label":"cytoskeleton","supporting_discovery_ids":[0,4,8,14]}],"pathway":[{"term_id":"R-HSA-162582","term_label":"Signal Transduction","supporting_discovery_ids":[1,12,18]},{"term_id":"R-HSA-1643685","term_label":"Disease","supporting_discovery_ids":[2,3,5,10]}],"complexes":["sarcomeric A-band (C-zone thick filament)"],"partners":["MYH7","ACTC1","TPM1","PRKD1","PRKACA"],"other_free_text":[]},"mechanistic_narrative":"MYBPC3 encodes cardiac myosin-binding protein C (cMyBP-C), a sarcomeric thick-filament regulatory protein that modulates cardiac contraction and relaxation by constraining myosin head proximity to actin and tuning thin-filament activation. The N-terminal domains (C0–C7) bind both the myosin S2 segment and F-actin, positioning tropomyosin to regulate Ca²⁺-dependent cross-bridge cycling, dampen spontaneous oscillatory contractions, and mediate myofilament Ca²⁺ sensitivity, while multi-site phosphorylation by PKA, CaMKII, PKC, and PKD at Ser273/Ser282/Ser302/Ser315 relieves the myosin head tether and differentially modulates contractile kinetics and tension [PMID:10024460, PMID:18599866, PMID:32078438, PMID:26718724, PMID:22636676, PMID:24606935]. The C-terminal C10 domain anchors cMyBP-C to the myosin rod (LMM), and disruption of this interaction abolishes sarcomeric incorporation [PMID:25583989]. MYBPC3 is the most commonly mutated gene in hypertrophic cardiomyopathy (HCM): truncating mutations undergo nonsense-mediated mRNA decay leading to protein haploinsufficiency that reciprocally augments myosin ATPase activity, reduces the super-relaxed myosin state, increases myofilament Ca²⁺ sensitivity, and impairs relaxation, while nontruncating pathogenic variants cause haploinsufficiency through defective splicing or accelerated protein degradation [PMID:19574547, PMID:30674652, PMID:15249187, PMID:34097875, PMID:32841044]."},"prefetch_data":{"uniprot":{"accession":"Q14896","full_name":"Myosin-binding protein C, cardiac-type","aliases":["C-protein, cardiac muscle isoform"],"length_aa":1274,"mass_kda":140.8,"function":"Thick filament-associated protein located in the crossbridge region of vertebrate striated muscle a bands. In vitro it binds MHC, F-actin and native thin filaments, and modifies the activity of actin-activated myosin ATPase. It may modulate muscle contraction or may play a more structural role","subcellular_location":"","url":"https://www.uniprot.org/uniprotkb/Q14896/entry"},"depmap":{"release":"DepMap","has_data":true,"is_common_essential":false,"resolved_as":"","url":"https://depmap.org/portal/gene/MYBPC3","classification":"Not Classified","n_dependent_lines":10,"n_total_lines":1208,"dependency_fraction":0.008278145695364239},"opencell":{"profiled":false,"resolved_as":"","ensg_id":"","cell_line_id":"","localizations":[],"interactors":[],"url":"https://opencell.sf.czbiohub.org/search/MYBPC3","total_profiled":1310},"omim":[{"mim_id":"615396","title":"LEFT VENTRICULAR NONCOMPACTION 10; LVNC10","url":"https://www.omim.org/entry/615396"},{"mim_id":"614335","title":"ARTHROGRYPOSIS, DISTAL, TYPE 1B; DA1B","url":"https://www.omim.org/entry/614335"},{"mim_id":"613874","title":"CARDIOMYOPATHY, FAMILIAL HYPERTROPHIC, 18; CMH18","url":"https://www.omim.org/entry/613874"},{"mim_id":"613765","title":"CARDIOMYOPATHY, FAMILIAL HYPERTROPHIC, 9; CMH9","url":"https://www.omim.org/entry/613765"},{"mim_id":"613251","title":"CARDIOMYOPATHY, FAMILIAL HYPERTROPHIC, 14; CMH14","url":"https://www.omim.org/entry/613251"}],"hpa":{"profiled":true,"resolved_as":"","reliability":"","locations":[],"tissue_specificity":"Tissue enriched","tissue_distribution":"Detected in some","driving_tissues":[{"tissue":"heart muscle","ntpm":1615.9}],"url":"https://www.proteinatlas.org/search/MYBPC3"},"hgnc":{"alias_symbol":["FHC","cMyBP-C"],"prev_symbol":["CMH4"]},"alphafold":{"accession":"Q14896","domains":[{"cath_id":"2.60.40.10","chopping":"13-96","consensus_level":"high","plddt":88.9029,"start":13,"end":96},{"cath_id":"2.60.40.10","chopping":"158-260","consensus_level":"high","plddt":83.3568,"start":158,"end":260},{"cath_id":"-","chopping":"331-358","consensus_level":"medium","plddt":66.2254,"start":331,"end":358},{"cath_id":"2.60.40.10","chopping":"457-542","consensus_level":"medium","plddt":86.7147,"start":457,"end":542},{"cath_id":"2.60.40.10","chopping":"545-637","consensus_level":"medium","plddt":87.2047,"start":545,"end":637},{"cath_id":"2.60.40.10","chopping":"874-965","consensus_level":"medium","plddt":89.5523,"start":874,"end":965},{"cath_id":"2.60.40.10","chopping":"1182-1270","consensus_level":"medium","plddt":87.2985,"start":1182,"end":1270}],"viewer_url":"https://alphafold.ebi.ac.uk/entry/Q14896","model_url":"https://alphafold.ebi.ac.uk/files/AF-Q14896-F1-model_v6.cif","pae_url":"https://alphafold.ebi.ac.uk/files/AF-Q14896-F1-predicted_aligned_error_v6.png","plddt_mean":78.81},"mouse_models":{"mgi_url":"https://www.informatics.jax.org/marker/summary?nomen=MYBPC3","jax_strain_url":"https://www.jax.org/strain/search?query=MYBPC3"},"sequence":{"accession":"Q14896","fasta_url":"https://rest.uniprot.org/uniprotkb/Q14896.fasta","uniprot_url":"https://www.uniprot.org/uniprotkb/Q14896/entry","alphafold_viewer_url":"https://alphafold.ebi.ac.uk/entry/Q14896"}},"corpus_meta":[{"pmid":"19151713","id":"PMC_19151713","title":"A common MYBPC3 (cardiac myosin binding protein C) variant associated with cardiomyopathies in South Asia.","date":"2009","source":"Nature genetics","url":"https://pubmed.ncbi.nlm.nih.gov/19151713","citation_count":218,"is_preprint":false},{"pmid":"10024460","id":"PMC_10024460","title":"Mutations in beta-myosin S2 that cause familial hypertrophic cardiomyopathy (FHC) abolish the interaction with the regulatory domain of myosin-binding protein-C.","date":"1999","source":"Journal of molecular biology","url":"https://pubmed.ncbi.nlm.nih.gov/10024460","citation_count":202,"is_preprint":false},{"pmid":"20215591","id":"PMC_20215591","title":"Coding sequence rare variants identified in MYBPC3, MYH6, TPM1, TNNC1, and TNNI3 from 312 patients with familial or idiopathic dilated cardiomyopathy.","date":"2010","source":"Circulation. Cardiovascular genetics","url":"https://pubmed.ncbi.nlm.nih.gov/20215591","citation_count":199,"is_preprint":false},{"pmid":"19574547","id":"PMC_19574547","title":"Evidence from human myectomy samples that MYBPC3 mutations cause hypertrophic cardiomyopathy through haploinsufficiency.","date":"2009","source":"Circulation research","url":"https://pubmed.ncbi.nlm.nih.gov/19574547","citation_count":198,"is_preprint":false},{"pmid":"26358504","id":"PMC_26358504","title":"Cardiac myosin-binding protein C (MYBPC3) in cardiac pathophysiology.","date":"2015","source":"Gene","url":"https://pubmed.ncbi.nlm.nih.gov/26358504","citation_count":178,"is_preprint":false},{"pmid":"30674652","id":"PMC_30674652","title":"Hypertrophic cardiomyopathy mutations in MYBPC3 dysregulate myosin.","date":"2019","source":"Science translational medicine","url":"https://pubmed.ncbi.nlm.nih.gov/30674652","citation_count":157,"is_preprint":false},{"pmid":"26489474","id":"PMC_26489474","title":"Contractile Defect Caused by Mutation in MYBPC3 Revealed under Conditions Optimized for Human PSC-Cardiomyocyte Function.","date":"2015","source":"Cell reports","url":"https://pubmed.ncbi.nlm.nih.gov/26489474","citation_count":157,"is_preprint":false},{"pmid":"15249187","id":"PMC_15249187","title":"Asymmetric septal hypertrophy in heterozygous cMyBP-C null mice.","date":"2004","source":"Cardiovascular research","url":"https://pubmed.ncbi.nlm.nih.gov/15249187","citation_count":123,"is_preprint":false},{"pmid":"22465693","id":"PMC_22465693","title":"Increased myofilament Ca2+ sensitivity and diastolic dysfunction as early consequences of Mybpc3 mutation in heterozygous knock-in mice.","date":"2012","source":"Journal of molecular and cellular cardiology","url":"https://pubmed.ncbi.nlm.nih.gov/22465693","citation_count":122,"is_preprint":false},{"pmid":"30586709","id":"PMC_30586709","title":"A Premature Termination Codon Mutation in MYBPC3 Causes Hypertrophic Cardiomyopathy via Chronic Activation of Nonsense-Mediated Decay.","date":"2019","source":"Circulation","url":"https://pubmed.ncbi.nlm.nih.gov/30586709","citation_count":105,"is_preprint":false},{"pmid":"18599866","id":"PMC_18599866","title":"Protein kinase A-mediated phosphorylation of cMyBP-C increases proximity of myosin heads to actin in resting myocardium.","date":"2008","source":"Circulation research","url":"https://pubmed.ncbi.nlm.nih.gov/18599866","citation_count":103,"is_preprint":false},{"pmid":"22057632","id":"PMC_22057632","title":"How do MYBPC3 mutations cause hypertrophic cardiomyopathy?","date":"2011","source":"Journal of muscle research and cell motility","url":"https://pubmed.ncbi.nlm.nih.gov/22057632","citation_count":90,"is_preprint":false},{"pmid":"22189562","id":"PMC_22189562","title":"Defective proteolytic systems in Mybpc3-targeted mice with cardiac hypertrophy.","date":"2011","source":"Basic research in cardiology","url":"https://pubmed.ncbi.nlm.nih.gov/22189562","citation_count":87,"is_preprint":false},{"pmid":"23716398","id":"PMC_23716398","title":"Rescue of cardiomyopathy through U7snRNA-mediated exon skipping in Mybpc3-targeted knock-in mice.","date":"2013","source":"EMBO molecular medicine","url":"https://pubmed.ncbi.nlm.nih.gov/23716398","citation_count":86,"is_preprint":false},{"pmid":"31015724","id":"PMC_31015724","title":"Contractile deficits in engineered cardiac microtissues as a result of MYBPC3 deficiency and mechanical overload.","date":"2018","source":"Nature biomedical engineering","url":"https://pubmed.ncbi.nlm.nih.gov/31015724","citation_count":80,"is_preprint":false},{"pmid":"28679633","id":"PMC_28679633","title":"Identification of pathogenic gene mutations in LMNA and MYBPC3 that alter RNA splicing.","date":"2017","source":"Proceedings of the National Academy of Sciences of the United States of America","url":"https://pubmed.ncbi.nlm.nih.gov/28679633","citation_count":79,"is_preprint":false},{"pmid":"28624223","id":"PMC_28624223","title":"Evaluation of MYBPC3 trans-Splicing and Gene Replacement as Therapeutic Options in Human iPSC-Derived Cardiomyocytes.","date":"2017","source":"Molecular therapy. Nucleic acids","url":"https://pubmed.ncbi.nlm.nih.gov/28624223","citation_count":78,"is_preprint":false},{"pmid":"31877118","id":"PMC_31877118","title":"Effects of MYBPC3 loss-of-function mutations preceding hypertrophic cardiomyopathy.","date":"2020","source":"JCI insight","url":"https://pubmed.ncbi.nlm.nih.gov/31877118","citation_count":73,"is_preprint":false},{"pmid":"32841044","id":"PMC_32841044","title":"Spatial and Functional Distribution of MYBPC3 Pathogenic Variants and Clinical Outcomes in Patients With Hypertrophic Cardiomyopathy.","date":"2020","source":"Circulation. Genomic and precision medicine","url":"https://pubmed.ncbi.nlm.nih.gov/32841044","citation_count":71,"is_preprint":false},{"pmid":"9472671","id":"PMC_9472671","title":"Characterization of T cells and cytokines in the aqueous humour (AH) in patients with Fuchs' heterochromic cyclitis (FHC) and idiopathic anterior uveitis (IAU).","date":"1998","source":"Clinical and experimental immunology","url":"https://pubmed.ncbi.nlm.nih.gov/9472671","citation_count":65,"is_preprint":false},{"pmid":"23896226","id":"PMC_23896226","title":"Contractile abnormalities and altered drug response in engineered heart tissue from Mybpc3-targeted knock-in mice.","date":"2013","source":"Journal of molecular and cellular cardiology","url":"https://pubmed.ncbi.nlm.nih.gov/23896226","citation_count":65,"is_preprint":false},{"pmid":"37741320","id":"PMC_37741320","title":"Spermidine suppresses oxidative stress and ferroptosis by Nrf2/HO-1/GPX4 and Akt/FHC/ACSL4 pathway to alleviate ovarian damage.","date":"2023","source":"Life sciences","url":"https://pubmed.ncbi.nlm.nih.gov/37741320","citation_count":64,"is_preprint":false},{"pmid":"15001446","id":"PMC_15001446","title":"Differential cross-bridge kinetics of FHC myosin mutations R403Q and R453C in heterozygous mouse myocardium.","date":"2004","source":"American journal of physiology. Heart and circulatory physiology","url":"https://pubmed.ncbi.nlm.nih.gov/15001446","citation_count":62,"is_preprint":false},{"pmid":"21601575","id":"PMC_21601575","title":"Electron microscopy and 3D reconstruction of F-actin decorated with cardiac myosin-binding protein C (cMyBP-C).","date":"2011","source":"Journal of molecular biology","url":"https://pubmed.ncbi.nlm.nih.gov/21601575","citation_count":62,"is_preprint":false},{"pmid":"23820890","id":"PMC_23820890","title":"Repair of Mybpc3 mRNA by 5'-trans-splicing in a Mouse Model of Hypertrophic Cardiomyopathy.","date":"2013","source":"Molecular therapy. Nucleic acids","url":"https://pubmed.ncbi.nlm.nih.gov/23820890","citation_count":60,"is_preprint":false},{"pmid":"25463273","id":"PMC_25463273","title":"Haploinsufficiency of MYBPC3 exacerbates the development of hypertrophic cardiomyopathy in heterozygous mice.","date":"2014","source":"Journal of molecular and cellular cardiology","url":"https://pubmed.ncbi.nlm.nih.gov/25463273","citation_count":59,"is_preprint":false},{"pmid":"19150014","id":"PMC_19150014","title":"[Mutations in sarcomeric genes MYH7, MYBPC3, TNNT2, TNNI3, and TPM1 in patients with hypertrophic cardiomyopathy].","date":"2009","source":"Revista espanola de cardiologia","url":"https://pubmed.ncbi.nlm.nih.gov/19150014","citation_count":58,"is_preprint":false},{"pmid":"12788380","id":"PMC_12788380","title":"Novel deletions in MYH7 and MYBPC3 identified in Indian families with familial hypertrophic cardiomyopathy.","date":"2003","source":"Journal of molecular and cellular cardiology","url":"https://pubmed.ncbi.nlm.nih.gov/12788380","citation_count":57,"is_preprint":false},{"pmid":"25078086","id":"PMC_25078086","title":"Nationwide study on hypertrophic cardiomyopathy in Iceland: evidence of a MYBPC3 founder mutation.","date":"2014","source":"Circulation","url":"https://pubmed.ncbi.nlm.nih.gov/25078086","citation_count":55,"is_preprint":false},{"pmid":"16837010","id":"PMC_16837010","title":"Prolonged Ca2+ and force transients in myosin RLC transgenic mouse fibers expressing malignant and benign FHC mutations.","date":"2006","source":"Journal of molecular biology","url":"https://pubmed.ncbi.nlm.nih.gov/16837010","citation_count":54,"is_preprint":false},{"pmid":"29021349","id":"PMC_29021349","title":"Activation of Autophagy Ameliorates Cardiomyopathy in Mybpc3-Targeted Knockin Mice.","date":"2017","source":"Circulation. Heart failure","url":"https://pubmed.ncbi.nlm.nih.gov/29021349","citation_count":53,"is_preprint":false},{"pmid":"27108529","id":"PMC_27108529","title":"Comparison of the effects of a truncating and a missense MYBPC3 mutation on contractile parameters of engineered heart tissue.","date":"2016","source":"Journal of molecular and cellular cardiology","url":"https://pubmed.ncbi.nlm.nih.gov/27108529","citation_count":53,"is_preprint":false},{"pmid":"18467358","id":"PMC_18467358","title":"Homozygous mutation of MYBPC3 associated with severe infantile hypertrophic cardiomyopathy at high frequency among the Amish.","date":"2008","source":"Heart (British Cardiac Society)","url":"https://pubmed.ncbi.nlm.nih.gov/18467358","citation_count":52,"is_preprint":false},{"pmid":"37445689","id":"PMC_37445689","title":"An Update on MYBPC3 Gene Mutation in Hypertrophic Cardiomyopathy.","date":"2023","source":"International journal of molecular sciences","url":"https://pubmed.ncbi.nlm.nih.gov/37445689","citation_count":51,"is_preprint":false},{"pmid":"24464755","id":"PMC_24464755","title":"Contractile dysfunction in a mouse model expressing a heterozygous MYBPC3 mutation associated with hypertrophic cardiomyopathy.","date":"2014","source":"American journal of physiology. Heart and circulatory physiology","url":"https://pubmed.ncbi.nlm.nih.gov/24464755","citation_count":51,"is_preprint":false},{"pmid":"24083979","id":"PMC_24083979","title":"MicroRNA transcriptome profiling in cardiac tissue of hypertrophic cardiomyopathy patients with MYBPC3 mutations.","date":"2013","source":"Journal of molecular and cellular cardiology","url":"https://pubmed.ncbi.nlm.nih.gov/24083979","citation_count":51,"is_preprint":false},{"pmid":"22021246","id":"PMC_22021246","title":"Carriers of the hypertrophic cardiomyopathy MYBPC3 mutation are characterized by reduced myocardial efficiency in the absence of hypertrophy and microvascular dysfunction.","date":"2011","source":"European journal of heart failure","url":"https://pubmed.ncbi.nlm.nih.gov/22021246","citation_count":48,"is_preprint":false},{"pmid":"30456444","id":"PMC_30456444","title":"Allelic imbalance and haploinsufficiency in MYBPC3-linked hypertrophic cardiomyopathy.","date":"2018","source":"Pflugers Archiv : European journal of physiology","url":"https://pubmed.ncbi.nlm.nih.gov/30456444","citation_count":46,"is_preprint":false},{"pmid":"17490679","id":"PMC_17490679","title":"Independent FHC-related cardiac troponin T mutations exhibit specific alterations in myocellular contractility and calcium kinetics.","date":"2007","source":"Journal of molecular and cellular cardiology","url":"https://pubmed.ncbi.nlm.nih.gov/17490679","citation_count":46,"is_preprint":false},{"pmid":"12123819","id":"PMC_12123819","title":"Generation of formate by the formyltransferase/hydrolase complex (Fhc) from Methylobacterium extorquens AM1.","date":"2002","source":"FEBS letters","url":"https://pubmed.ncbi.nlm.nih.gov/12123819","citation_count":46,"is_preprint":false},{"pmid":"24093860","id":"PMC_24093860","title":"Screening of MYH7, MYBPC3, and TNNT2 genes in Brazilian patients with hypertrophic cardiomyopathy.","date":"2013","source":"American heart journal","url":"https://pubmed.ncbi.nlm.nih.gov/24093860","citation_count":45,"is_preprint":false},{"pmid":"28193612","id":"PMC_28193612","title":"Lack of Phenotypic Differences by Cardiovascular Magnetic Resonance Imaging in MYH7 (β-Myosin Heavy Chain)- Versus MYBPC3 (Myosin-Binding Protein C)-Related Hypertrophic Cardiomyopathy.","date":"2017","source":"Circulation. Cardiovascular imaging","url":"https://pubmed.ncbi.nlm.nih.gov/28193612","citation_count":44,"is_preprint":false},{"pmid":"27955979","id":"PMC_27955979","title":"Cardiac inflammation in genetic dilated cardiomyopathy caused by MYBPC3 mutation.","date":"2016","source":"Journal of molecular and cellular cardiology","url":"https://pubmed.ncbi.nlm.nih.gov/27955979","citation_count":41,"is_preprint":false},{"pmid":"22076249","id":"PMC_22076249","title":"Adrenergic stress reveals septal hypertrophy and proteasome impairment in heterozygous Mybpc3-targeted knock-in mice.","date":"2011","source":"Journal of muscle research and cell motility","url":"https://pubmed.ncbi.nlm.nih.gov/22076249","citation_count":40,"is_preprint":false},{"pmid":"28774348","id":"PMC_28774348","title":"Epithelial-to-mesenchymal transition in FHC-silenced cells: the role of CXCR4/CXCL12 axis.","date":"2017","source":"Journal of experimental & clinical cancer research : CR","url":"https://pubmed.ncbi.nlm.nih.gov/28774348","citation_count":39,"is_preprint":false},{"pmid":"32612638","id":"PMC_32612638","title":"Genome-Wide Association Study Reveals a Novel Association Between MYBPC3 Gene Polymorphism, Endurance Athlete Status, Aerobic Capacity and Steroid Metabolism.","date":"2020","source":"Frontiers in genetics","url":"https://pubmed.ncbi.nlm.nih.gov/32612638","citation_count":39,"is_preprint":false},{"pmid":"25740977","id":"PMC_25740977","title":"A founder MYBPC3 mutation results in HCM with a high risk of sudden death after the fourth decade of life.","date":"2015","source":"Journal of medical genetics","url":"https://pubmed.ncbi.nlm.nih.gov/25740977","citation_count":38,"is_preprint":false},{"pmid":"26508994","id":"PMC_26508994","title":"Oxidative Stress in Dilated Cardiomyopathy Caused by MYBPC3 Mutation.","date":"2015","source":"Oxidative medicine and cellular longevity","url":"https://pubmed.ncbi.nlm.nih.gov/26508994","citation_count":37,"is_preprint":false},{"pmid":"21051304","id":"PMC_21051304","title":"Prevalence of the MYBPC3-A31P mutation in a large European feline population and association with hypertrophic cardiomyopathy in the Maine Coon breed.","date":"2010","source":"Journal of veterinary cardiology : the official journal of the European Society of Veterinary Cardiology","url":"https://pubmed.ncbi.nlm.nih.gov/21051304","citation_count":36,"is_preprint":false},{"pmid":"22089698","id":"PMC_22089698","title":"cMyBP-C as a promiscuous substrate: phosphorylation by non-PKA kinases and its potential significance.","date":"2011","source":"Journal of muscle research and cell motility","url":"https://pubmed.ncbi.nlm.nih.gov/22089698","citation_count":35,"is_preprint":false},{"pmid":"32163302","id":"PMC_32163302","title":"Reevaluation of the South Asian MYBPC3Δ25bp Intronic Deletion in Hypertrophic Cardiomyopathy.","date":"2020","source":"Circulation. Genomic and precision medicine","url":"https://pubmed.ncbi.nlm.nih.gov/32163302","citation_count":35,"is_preprint":false},{"pmid":"32525266","id":"PMC_32525266","title":"Radiomic Analysis of Native T1 Mapping Images Discriminates Between MYH7 and MYBPC3-Related Hypertrophic Cardiomyopathy.","date":"2020","source":"Journal of magnetic resonance imaging : JMRI","url":"https://pubmed.ncbi.nlm.nih.gov/32525266","citation_count":35,"is_preprint":false},{"pmid":"32078438","id":"PMC_32078438","title":"A Novel \"Cut and Paste\" Method for In Situ Replacement of cMyBP-C Reveals a New Role for cMyBP-C in the Regulation of Contractile Oscillations.","date":"2020","source":"Circulation research","url":"https://pubmed.ncbi.nlm.nih.gov/32078438","citation_count":34,"is_preprint":false},{"pmid":"33049255","id":"PMC_33049255","title":"Targeting the population for gene therapy with MYBPC3.","date":"2020","source":"Journal of molecular and cellular cardiology","url":"https://pubmed.ncbi.nlm.nih.gov/33049255","citation_count":33,"is_preprint":false},{"pmid":"24337823","id":"PMC_24337823","title":"MYBPC3 in hypertrophic cardiomyopathy: from mutation identification to RNA-based correction.","date":"2013","source":"Pflugers Archiv : European journal of physiology","url":"https://pubmed.ncbi.nlm.nih.gov/24337823","citation_count":33,"is_preprint":false},{"pmid":"34097875","id":"PMC_34097875","title":"Protein haploinsufficiency drivers identify MYBPC3 variants that cause hypertrophic cardiomyopathy.","date":"2021","source":"The Journal of biological chemistry","url":"https://pubmed.ncbi.nlm.nih.gov/34097875","citation_count":33,"is_preprint":false},{"pmid":"26825555","id":"PMC_26825555","title":"Selective phosphorylation of PKA targets after β-adrenergic receptor stimulation impairs myofilament function in Mybpc3-targeted HCM mouse model.","date":"2016","source":"Cardiovascular research","url":"https://pubmed.ncbi.nlm.nih.gov/26825555","citation_count":33,"is_preprint":false},{"pmid":"12601548","id":"PMC_12601548","title":"Molecular genetics of familial hypertrophic cardiomyopathy (FHC).","date":"2003","source":"Journal of human genetics","url":"https://pubmed.ncbi.nlm.nih.gov/12601548","citation_count":32,"is_preprint":false},{"pmid":"36357371","id":"PMC_36357371","title":"MYBPC3 deficiency in cardiac fibroblasts drives their activation and contributes to fibrosis.","date":"2022","source":"Cell death & disease","url":"https://pubmed.ncbi.nlm.nih.gov/36357371","citation_count":32,"is_preprint":false},{"pmid":"30410445","id":"PMC_30410445","title":"Transcriptome Analysis of Cardiac Hypertrophic Growth in MYBPC3-Null Mice Suggests Early Responders in Hypertrophic Remodeling.","date":"2018","source":"Frontiers in physiology","url":"https://pubmed.ncbi.nlm.nih.gov/30410445","citation_count":32,"is_preprint":false},{"pmid":"29641836","id":"PMC_29641836","title":"Association of Cardiomyopathy With MYBPC3 D389V and MYBPC3Δ25bpIntronic Deletion in South Asian Descendants.","date":"2018","source":"JAMA cardiology","url":"https://pubmed.ncbi.nlm.nih.gov/29641836","citation_count":31,"is_preprint":false},{"pmid":"17122190","id":"PMC_17122190","title":"In vivo left ventricular functional capacity is compromised in cMyBP-C null mice.","date":"2006","source":"American journal of physiology. Heart and circulatory physiology","url":"https://pubmed.ncbi.nlm.nih.gov/17122190","citation_count":31,"is_preprint":false},{"pmid":"25346696","id":"PMC_25346696","title":"Familial hypertrophic cardiomyopathy: functional variance among individual cardiomyocytes as a trigger of FHC-phenotype development.","date":"2014","source":"Frontiers in physiology","url":"https://pubmed.ncbi.nlm.nih.gov/25346696","citation_count":31,"is_preprint":false},{"pmid":"24906243","id":"PMC_24906243","title":"Association of the myosin binding protein C3 mutation (MYBPC3 R820W) with cardiac death in a survey of 236 Ragdoll cats.","date":"2014","source":"Journal of veterinary cardiology : the official journal of the European Society of Veterinary Cardiology","url":"https://pubmed.ncbi.nlm.nih.gov/24906243","citation_count":31,"is_preprint":false},{"pmid":"26090888","id":"PMC_26090888","title":"Screening Mutations of MYBPC3 in 114 Unrelated Patients with Hypertrophic Cardiomyopathy by Targeted Capture and Next-generation Sequencing.","date":"2015","source":"Scientific reports","url":"https://pubmed.ncbi.nlm.nih.gov/26090888","citation_count":31,"is_preprint":false},{"pmid":"30924982","id":"PMC_30924982","title":"Biallelic mutation in MYH7 and MYBPC3 leads to severe cardiomyopathy with left ventricular noncompaction phenotype.","date":"2019","source":"Human mutation","url":"https://pubmed.ncbi.nlm.nih.gov/30924982","citation_count":30,"is_preprint":false},{"pmid":"30645170","id":"PMC_30645170","title":"Key Value of RNA Analysis of MYBPC3 Splice-Site Variants in Hypertrophic Cardiomyopathy.","date":"2019","source":"Circulation. Genomic and precision medicine","url":"https://pubmed.ncbi.nlm.nih.gov/30645170","citation_count":30,"is_preprint":false},{"pmid":"23980194","id":"PMC_23980194","title":"E258K HCM-causing mutation in cardiac MyBP-C reduces contractile force and accelerates twitch kinetics by disrupting the cMyBP-C and myosin S2 interaction.","date":"2013","source":"The Journal of general physiology","url":"https://pubmed.ncbi.nlm.nih.gov/23980194","citation_count":30,"is_preprint":false},{"pmid":"19219553","id":"PMC_19219553","title":"From genotype to phenotype: a longitudinal study of a patient with hypertrophic cardiomyopathy due to a mutation in the MYBPC3 gene.","date":"2009","source":"Journal of muscle research and cell motility","url":"https://pubmed.ncbi.nlm.nih.gov/19219553","citation_count":29,"is_preprint":false},{"pmid":"22907696","id":"PMC_22907696","title":"A case of compound mutations in the MYBPC3 gene associated with biventricular hypertrophy and neonatal death.","date":"2012","source":"Neonatology","url":"https://pubmed.ncbi.nlm.nih.gov/22907696","citation_count":28,"is_preprint":false},{"pmid":"40038304","id":"PMC_40038304","title":"AAV9-mediated MYBPC3 gene therapy with optimized expression cassette enhances cardiac function and survival in MYBPC3 cardiomyopathy models.","date":"2025","source":"Nature communications","url":"https://pubmed.ncbi.nlm.nih.gov/40038304","citation_count":27,"is_preprint":false},{"pmid":"25010737","id":"PMC_25010737","title":"Sexual dimorphic response to exercise in hypertrophic cardiomyopathy-associated MYBPC3-targeted knock-in mice.","date":"2014","source":"Pflugers Archiv : European journal of physiology","url":"https://pubmed.ncbi.nlm.nih.gov/25010737","citation_count":27,"is_preprint":false},{"pmid":"21306647","id":"PMC_21306647","title":"Hypertrophic cardiomyopathy in young Maine Coon cats caused by the p.A31P cMyBP-C mutation--the clinical significance of having the mutation.","date":"2011","source":"Acta veterinaria Scandinavica","url":"https://pubmed.ncbi.nlm.nih.gov/21306647","citation_count":27,"is_preprint":false},{"pmid":"21959974","id":"PMC_21959974","title":"A low prevalence of MYH7/MYBPC3 mutations among familial hypertrophic cardiomyopathy patients in India.","date":"2011","source":"Molecular and cellular biochemistry","url":"https://pubmed.ncbi.nlm.nih.gov/21959974","citation_count":25,"is_preprint":false},{"pmid":"36744470","id":"PMC_36744470","title":"Slower Calcium Handling Balances Faster Cross-Bridge Cycling in Human MYBPC3 HCM.","date":"2023","source":"Circulation research","url":"https://pubmed.ncbi.nlm.nih.gov/36744470","citation_count":24,"is_preprint":false},{"pmid":"25583989","id":"PMC_25583989","title":"A hypertrophic cardiomyopathy-associated MYBPC3 mutation common in populations of South Asian descent causes contractile dysfunction.","date":"2015","source":"The Journal of biological chemistry","url":"https://pubmed.ncbi.nlm.nih.gov/25583989","citation_count":24,"is_preprint":false},{"pmid":"25281569","id":"PMC_25281569","title":"Compound heterozygosity deteriorates phenotypes of hypertrophic cardiomyopathy with founder MYBPC3 mutation: evidence from patients and zebrafish models.","date":"2014","source":"American journal of physiology. Heart and circulatory physiology","url":"https://pubmed.ncbi.nlm.nih.gov/25281569","citation_count":24,"is_preprint":false},{"pmid":"35224729","id":"PMC_35224729","title":"The mechanics of the heart: zooming in on hypertrophic cardiomyopathy and cMyBP-C.","date":"2022","source":"FEBS letters","url":"https://pubmed.ncbi.nlm.nih.gov/35224729","citation_count":23,"is_preprint":false},{"pmid":"24327208","id":"PMC_24327208","title":"MYBPC3's alternate ending: consequences and therapeutic implications of a highly prevalent 25 bp deletion mutation.","date":"2013","source":"Pflugers Archiv : European journal of physiology","url":"https://pubmed.ncbi.nlm.nih.gov/24327208","citation_count":23,"is_preprint":false},{"pmid":"30668650","id":"PMC_30668650","title":"Assessment of myocardial oxygenation, strain, and diastology in MYBPC3-related hypertrophic cardiomyopathy: a cardiovascular magnetic resonance and echocardiography study.","date":"2019","source":"European heart journal. Cardiovascular Imaging","url":"https://pubmed.ncbi.nlm.nih.gov/30668650","citation_count":23,"is_preprint":false},{"pmid":"26718724","id":"PMC_26718724","title":"The cMyBP-C HCM variant L348P enhances thin filament activation through an increased shift in tropomyosin position.","date":"2015","source":"Journal of molecular and cellular cardiology","url":"https://pubmed.ncbi.nlm.nih.gov/26718724","citation_count":22,"is_preprint":false},{"pmid":"33657327","id":"PMC_33657327","title":"Transcriptome Sequencing of Patients With Hypertrophic Cardiomyopathy Reveals Novel Splice-Altering Variants in MYBPC3.","date":"2021","source":"Circulation. Genomic and precision medicine","url":"https://pubmed.ncbi.nlm.nih.gov/33657327","citation_count":22,"is_preprint":false},{"pmid":"21915287","id":"PMC_21915287","title":"Association of 25 bp deletion in MYBPC3 gene with left ventricle dysfunction in coronary artery disease patients.","date":"2011","source":"PloS one","url":"https://pubmed.ncbi.nlm.nih.gov/21915287","citation_count":22,"is_preprint":false},{"pmid":"23140321","id":"PMC_23140321","title":"A human MYBPC3 mutation appearing about 10 centuries ago results in a hypertrophic cardiomyopathy with delayed onset, moderate evolution but with a risk of sudden death.","date":"2012","source":"BMC medical genetics","url":"https://pubmed.ncbi.nlm.nih.gov/23140321","citation_count":22,"is_preprint":false},{"pmid":"33757590","id":"PMC_33757590","title":"Multi-omics integration identifies key upstream regulators of pathomechanisms in hypertrophic cardiomyopathy due to truncating MYBPC3 mutations.","date":"2021","source":"Clinical epigenetics","url":"https://pubmed.ncbi.nlm.nih.gov/33757590","citation_count":21,"is_preprint":false},{"pmid":"22569109","id":"PMC_22569109","title":"The role of renin-angiotensin-aldosterone system polymorphisms in phenotypic expression of MYBPC3-related hypertrophic cardiomyopathy.","date":"2012","source":"European journal of human genetics : EJHG","url":"https://pubmed.ncbi.nlm.nih.gov/22569109","citation_count":21,"is_preprint":false},{"pmid":"23782526","id":"PMC_23782526","title":"Somatic MYH7, MYBPC3, TPM1, TNNT2 and TNNI3 mutations in sporadic hypertrophic cardiomyopathy.","date":"2013","source":"Circulation journal : official journal of the Japanese Circulation Society","url":"https://pubmed.ncbi.nlm.nih.gov/23782526","citation_count":20,"is_preprint":false},{"pmid":"24606935","id":"PMC_24606935","title":"Phosphorylation of cMyBP-C affects contractile mechanisms in a site-specific manner.","date":"2014","source":"Biophysical journal","url":"https://pubmed.ncbi.nlm.nih.gov/24606935","citation_count":19,"is_preprint":false},{"pmid":"23527136","id":"PMC_23527136","title":"Molecular modeling of disease causing mutations in domain C1 of cMyBP-C.","date":"2013","source":"PloS one","url":"https://pubmed.ncbi.nlm.nih.gov/23527136","citation_count":19,"is_preprint":false},{"pmid":"20193843","id":"PMC_20193843","title":"Fetal colon cell line FHC exhibits tumorigenic phenotype, complex karyotype, and TP53 gene mutation.","date":"2010","source":"Cancer genetics and cytogenetics","url":"https://pubmed.ncbi.nlm.nih.gov/20193843","citation_count":19,"is_preprint":false},{"pmid":"34542152","id":"PMC_34542152","title":"A genome-first approach to rare variants in hypertrophic cardiomyopathy genes MYBPC3 and MYH7 in a medical biobank.","date":"2022","source":"Human molecular genetics","url":"https://pubmed.ncbi.nlm.nih.gov/34542152","citation_count":18,"is_preprint":false},{"pmid":"28090637","id":"PMC_28090637","title":"Diltiazem prevents stress-induced contractile deficits in cardiomyocytes, but does not reverse the cardiomyopathy phenotype in Mybpc3-knock-in mice.","date":"2017","source":"The Journal of physiology","url":"https://pubmed.ncbi.nlm.nih.gov/28090637","citation_count":18,"is_preprint":false},{"pmid":"22636676","id":"PMC_22636676","title":"Protein kinase D increases maximal Ca2+-activated tension of cardiomyocyte contraction by phosphorylation of cMyBP-C-Ser315.","date":"2012","source":"American journal of physiology. Heart and circulatory physiology","url":"https://pubmed.ncbi.nlm.nih.gov/22636676","citation_count":18,"is_preprint":false},{"pmid":"37409452","id":"PMC_37409452","title":"Long-Term Prevalence of Systolic Dysfunction in MYBPC3 Versus MYH7-Related Hypertrophic Cardiomyopathy.","date":"2023","source":"Circulation. Genomic and precision medicine","url":"https://pubmed.ncbi.nlm.nih.gov/37409452","citation_count":17,"is_preprint":false},{"pmid":"23600722","id":"PMC_23600722","title":"AT1 blockade abolishes left ventricular hypertrophy in heterozygous cMyBP-C null mice: role of FHL1.","date":"2013","source":"Fundamental & clinical pharmacology","url":"https://pubmed.ncbi.nlm.nih.gov/23600722","citation_count":17,"is_preprint":false},{"pmid":"26267065","id":"PMC_26267065","title":"The Metabolome in Finnish Carriers of the MYBPC3-Q1061X Mutation for Hypertrophic Cardiomyopathy.","date":"2015","source":"PloS one","url":"https://pubmed.ncbi.nlm.nih.gov/26267065","citation_count":17,"is_preprint":false},{"pmid":"21298151","id":"PMC_21298151","title":"Lower sensitivity of FHC fetal colon epithelial cells to photodynamic therapy compared to HT-29 colon adenocarcinoma cells despite higher intracellular accumulation of hypericin.","date":"2011","source":"Photochemical & photobiological sciences : Official journal of the European Photochemistry Association and the European Society for Photobiology","url":"https://pubmed.ncbi.nlm.nih.gov/21298151","citation_count":17,"is_preprint":false},{"pmid":"36765144","id":"PMC_36765144","title":"Homology-directed repair of an MYBPC3 gene mutation in a rat model of hypertrophic cardiomyopathy.","date":"2023","source":"Gene therapy","url":"https://pubmed.ncbi.nlm.nih.gov/36765144","citation_count":16,"is_preprint":false},{"pmid":"26739353","id":"PMC_26739353","title":"Two COX-2 inhibitors induce apoptosis in human erythroleukemia K562cells by modulating NF-κB and FHC pathways.","date":"2016","source":"Daru : journal of Faculty of Pharmacy, Tehran University of Medical Sciences","url":"https://pubmed.ncbi.nlm.nih.gov/26739353","citation_count":16,"is_preprint":false},{"pmid":"34680864","id":"PMC_34680864","title":"Myocardial Deformation Analysis in MYBPC3 and MYH7 Related Sarcomeric Hypertrophic Cardiomyopathy-The Graz Hypertrophic Cardiomyopathy Registry.","date":"2021","source":"Genes","url":"https://pubmed.ncbi.nlm.nih.gov/34680864","citation_count":16,"is_preprint":false}],"cost":{"stage1":{"model":"claude-sonnet-4-6","input_tokens":56536,"output_tokens":5887,"usd":0.128957},"stage2":{"model":"claude-opus-4-6","input_tokens":9483,"output_tokens":4712,"usd":0.247823},"total_usd":0.37678,"stage1_batch_id":"msgbatch_012ZiiCUBfB62NCTQd4Bk1Jo","stage2_batch_id":"msgbatch_01Xuqq9aUHoQouS7UVGZNStZ","note":"batch pricing = 50% of standard"},"stage1_raw":"```json\n{\n  \"discoveries\": [\n    {\n      \"year\": 1999,\n      \"finding\": \"The MyBP-C motif (N-terminal regulatory domain of cardiac MyBP-C) binds to the N-terminal 126 residues of the myosin S2 segment; two FHC-causing mutations in beta-myosin S2 (R870H and E924K) drastically reduce or abolish this binding, suggesting cMyBP-C regulates contraction through this S2 interaction.\",\n      \"method\": \"In vitro binding assay (Kd measurements), fragment localization in cardiomyocytes and isolated myofibrils\",\n      \"journal\": \"Journal of molecular biology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — in vitro binding with quantitative Kd measurements plus functional localization, replicated concept across multiple FHC mutations\",\n      \"pmids\": [\"10024460\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2008,\n      \"finding\": \"PKA-mediated phosphorylation of cMyBP-C relieves a tether-like constraint on myosin heads, increasing their proximity to actin (azimuthal/radial displacement toward thin filaments) as measured by increased equatorial intensity ratio I(11)/I(10) in wild-type but not cMyBP-C null myocardium; cMyBP-C also stabilizes the myofilament lattice spacing.\",\n      \"method\": \"Synchrotron low-angle X-ray diffraction of skinned trabeculae from wild-type and cMyBP-C null mice with/without PKA treatment\",\n      \"journal\": \"Circulation research\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — direct structural measurement with rigorous null-mouse controls demonstrating cMyBP-C dependence\",\n      \"pmids\": [\"18599866\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2009,\n      \"finding\": \"MYBPC3 truncation and missense mutations cause haploinsufficiency: no truncated cMyBP-C protein is detectable in human myectomy tissue, and total myofibrillar cMyBP-C levels are significantly reduced (~76% of control) in MYBPC3-mutant HCM patients.\",\n      \"method\": \"Immunoblotting and RT-PCR of human myectomy samples vs. donor hearts\",\n      \"journal\": \"Circulation research\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — orthogonal protein and mRNA quantification in human tissue, multiple mutation types tested\",\n      \"pmids\": [\"19574547\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2004,\n      \"finding\": \"Heterozygous cMyBP-C null mice (one functional Mybpc3 allele) develop asymmetric septal hypertrophy with fibrosis, while homozygous null mice develop eccentric LV hypertrophy with impaired relaxation; establishing that partial cMyBP-C deficiency is sufficient to cause a key HCM phenotypic feature.\",\n      \"method\": \"Targeted deletion of exons 1–2 in mice; molecular, functional (echocardiography), and morphological analyses at multiple ages\",\n      \"journal\": \"Cardiovascular research\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — clean genetic KO with dose-dependent phenotype across heterozygous and homozygous animals, multiple readouts\",\n      \"pmids\": [\"15249187\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2011,\n      \"finding\": \"N-terminal cMyBP-C fragments bind to F-actin subdomain 1, with density extending tangentially toward actin's pointed end; this binding position could modulate tropomyosin position and interfere with myosin head binding to actin.\",\n      \"method\": \"Negative stain electron microscopy and 3D helical reconstruction of F-actin decorated with bacterially expressed N-terminal cMyBP-C fragments; atomic model fitting\",\n      \"journal\": \"Journal of molecular biology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — structural determination with 3D reconstruction and molecular fitting\",\n      \"pmids\": [\"21601575\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2012,\n      \"finding\": \"In Mybpc3 knock-in HCM mice, even before left ventricular hypertrophy develops, heterozygous mice exhibit increased myofilament Ca2+ sensitivity and diastolic dysfunction, indicating these are primary consequences of Mybpc3 mutation independent of hypertrophy.\",\n      \"method\": \"Skinned ventricular trabeculae force measurements, intact myocyte Ca2+ transients, echocardiography/Doppler in heterozygous and homozygous knock-in mice\",\n      \"journal\": \"Journal of molecular and cellular cardiology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — multiple orthogonal functional methods in well-characterized knock-in model with pre-hypertrophic time point\",\n      \"pmids\": [\"22465693\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2011,\n      \"finding\": \"Mybpc3-targeted knock-in mice show altered ubiquitin-proteasome system (UPS) and autophagy-lysosome pathway (ALP): early postnatal UPS activation, specific UPS impairment in old knock-in (but not knock-out) mice expressing truncated cMyBP-C, and defective ALP-mediated degradation in both models, implicating proteolytic dysfunction in HCM pathogenesis.\",\n      \"method\": \"Ub(G76V)-GFP reporter mouse crosses, proteasomal activity assays, ALP marker quantification in KI and KO mice\",\n      \"journal\": \"Basic research in cardiology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — reporter mouse assay with KI vs. KO comparison, but mechanism not fully reconstituted\",\n      \"pmids\": [\"22189562\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2013,\n      \"finding\": \"The HCM-causing E258K missense mutation in cMyBP-C abolishes interaction between the N-terminal cMyBP-C and myosin S2 (assessed by yeast two-hybrid) and increases affinity for actin, causing accelerated contractile kinetics and severely reduced twitch force in engineered cardiac tissue.\",\n      \"method\": \"Adenoviral gene transfer in cMyBP-C null murine engineered cardiac tissue; yeast two-hybrid; force measurements; phosphorylation analysis\",\n      \"journal\": \"The Journal of general physiology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1–2 — multiple orthogonal methods (yeast two-hybrid, functional reconstitution in tissue model, phosphorylation analysis) in single study\",\n      \"pmids\": [\"23980194\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2015,\n      \"finding\": \"The South Asian MYBPC3 25-bp deletion mutation produces a C10 domain variant (cMyBP-CC10mut) that fails to localize to the C-zone of the sarcomere, cannot interact with myosin LMM, resides predominantly in the soluble fraction, and causes reduced fractional shortening and sarcomere relaxation without affecting Ca2+ transients.\",\n      \"method\": \"Adenoviral expression in adult rat cardiomyocytes; immunofluorescence; subcellular fractionation; co-sedimentation and protein cross-linking assays; protein homology modeling\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1–2 — multiple orthogonal biochemical and cell biology methods establishing mechanism\",\n      \"pmids\": [\"25583989\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2015,\n      \"finding\": \"The HCM-associated L348P mutation in the M-domain of cMyBP-C causes a gain-of-function by shifting tropomyosin to approximately the open position on thin filaments (larger than the closed-position shift caused by wild-type), enhancing Ca2+-sensitization in a phosphorylation-independent manner.\",\n      \"method\": \"Electron microscopy and 3D reconstruction of thin filaments decorated with L348P-mutant vs. wild-type and phosphorylated N-terminal cMyBP-C fragments\",\n      \"journal\": \"Journal of molecular and cellular cardiology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — structural 3D reconstruction with direct comparison of WT, phosphorylated, and mutant fragments\",\n      \"pmids\": [\"26718724\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2019,\n      \"finding\": \"Stepwise depletion of cMyBP-C causes reciprocal augmentation of myosin contractility; cMyBP-C depletion enhances the myosin state enabling ATP hydrolysis and thin filament interactions while reducing the super-relaxed (energy-conserving) conformation; the myosin ATPase inhibitor MYK-461 rescues relaxation deficits caused by MYBPC3 mutations.\",\n      \"method\": \"Genetic and biochemical approaches in mouse and human cardiomyocytes with MYBPC3 mutations; myosin conformation assays; pharmacological rescue with MYK-461\",\n      \"journal\": \"Science translational medicine\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1–2 — multiple orthogonal genetic/biochemical methods, pharmacological rescue in two cell systems\",\n      \"pmids\": [\"30674652\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2019,\n      \"finding\": \"MYBPC3 premature termination codon mutations chronically activate the nonsense-mediated decay (NMD) pathway, leading to aberrant calcium handling (prolonged decay kinetics, elevated diastolic Ca2+) in iPSC-CMs; specific NMD inhibition reverses the molecular phenotype and normalizes calcium handling.\",\n      \"method\": \"Isogenic iPSC-CMs from HCM patients; comprehensive phenotypic and transcriptome analyses; pharmacological NMD inhibition\",\n      \"journal\": \"Circulation\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — isogenic system with pharmacological rescue providing direct mechanistic link between NMD activation and Ca2+ phenotype\",\n      \"pmids\": [\"30586709\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2012,\n      \"finding\": \"Protein kinase D (PKD) binds to cMyBP-C in contracting cardiomyocytes and phosphorylates it at Ser315; PKD-mediated phosphorylation of cMyBP-C increases maximal Ca2+-activated tension (Tmax) in wild-type but not cMyBP-C KO skinned myocytes, establishing cMyBP-C as essential for PKD's effect on Tmax.\",\n      \"method\": \"Immunoprecipitation; permeabilized ventricular myocytes from WT and cMyBP-C KO mice incubated with active PKD; force measurements\",\n      \"journal\": \"American journal of physiology. Heart and circulatory physiology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1–2 — Co-IP establishing binding, KO rescue experiment establishing functional requirement\",\n      \"pmids\": [\"22636676\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2014,\n      \"finding\": \"Site-specific phosphorylation of cMyBP-C differentially affects contractile mechanisms: the DAD phosphomimetic (Asp273-Ala282-Asp302) significantly decreases isometric tension, stiffness, and cross-bridge kinetics (2πc), while SAS and ADA variants cause minimal changes, demonstrating that Ser282 in its non-phosphorylated state combined with phosphomimetic residues at 273/302 is detrimental.\",\n      \"method\": \"Sinusoidal analysis in papillary/trabecular fibers from cMyBP-C null mice expressing site-specific phosphorylation mutant transgenes (ADA, DAD, SAS) vs. WT\",\n      \"journal\": \"Biophysical journal\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — in vitro reconstitution with specific phosphosite mutations and rigorous mechanical analysis\",\n      \"pmids\": [\"24606935\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2020,\n      \"finding\": \"Acute removal of cMyBP-C N-terminal domains (C0–C7) from sarcomeres in situ reduces myofilament Ca2+ sensitivity, increases cross-bridge cycling rate (ktr), and induces spontaneous oscillatory contractions (SPOC) at submaximal Ca2+; ligation of recombinant C0-C7 rescues pCa50 and ktr and abolishes oscillations, while phosphorylated C0-C7 is less effective, revealing a novel role for cMyBP-C N-terminal domains in damping sarcomere-driven contractile waves.\",\n      \"method\": \"Novel 'cut and paste' approach using TEVp cleavage and SpyCatcher/SpyTag system in detergent-permeabilized cardiomyocytes from gene-edited Spy-C mice; force measurements\",\n      \"journal\": \"Circulation research\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — reconstitution with acute domain removal and re-ligation, functional rescue with phosphorylation variant comparison\",\n      \"pmids\": [\"32078438\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2006,\n      \"finding\": \"cMyBP-C is required for normal in vivo LV function: cMyBP-C null mice show compromised systolic and diastolic function, and lack the contractile improvement normally seen with beta-adrenergic stimulation or pressure overload adaptation, indicating cMyBP-C is necessary for adrenergic-mediated enhancement of contractility.\",\n      \"method\": \"Pressure-volume relations and echocardiography in cMyBP-C null vs. wild-type mice; beta-adrenergic stimulation; aortic banding\",\n      \"journal\": \"American journal of physiology. Heart and circulatory physiology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — clean genetic null with multiple in vivo readouts and pharmacological challenge\",\n      \"pmids\": [\"17122190\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2020,\n      \"finding\": \"Heterozygous MYBPC3 frameshift mutations cause allelic loss of function (reduced WT mRNA) but MyBP-C protein levels are maintained through reduced degradation rate (not increased synthesis), indicating cardiomyocytes have an innate protein-level compensatory mechanism for MyBP-C stoichiometry.\",\n      \"method\": \"Patient and genome-engineered iPSC-CMs; stable isotope labeling to measure synthesis and degradation rates; RNA-Seq; contractile function assays\",\n      \"journal\": \"JCI insight\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — stable isotope pulse-chase directly measuring synthesis/degradation rates with isogenic controls\",\n      \"pmids\": [\"31877118\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2020,\n      \"finding\": \"Nontruncating MYBPC3 pathogenic missense variants cluster in domains C3, C6, and C10; C10 domain missense variants fail to incorporate into myofilaments and have ~90% accelerated degradation rates, while C3 and C6 variants incorporate normally with similar degradation to wild-type, revealing domain-specific loss-of-function mechanisms.\",\n      \"method\": \"Expression of mutant MyBP-C in rat ventricular myocytes; immunofluorescence for myofilament localization; degradation rate measurements\",\n      \"journal\": \"Circulation. Genomic and precision medicine\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — direct cell-based localization and degradation assays across multiple pathogenic variants\",\n      \"pmids\": [\"32841044\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2016,\n      \"finding\": \"In Mybpc3 knock-in HCM mice, beta-adrenergic stimulation causes preferential PKA phosphorylation of phospholamban (PLN) over cardiac troponin I (cTnI), resulting in impaired myofilament contractile and lusitropic response despite maintained Ca2+ handling response.\",\n      \"method\": \"Permeabilized and intact cardiomyocytes from HET and KI Mybpc3 knock-in mice; phosphorylation state measurements; sarcomere length and force measurements; isoprenaline stimulation\",\n      \"journal\": \"Cardiovascular research\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — direct phosphorylation measurements in knock-in cardiomyocytes, single lab\",\n      \"pmids\": [\"26825555\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2017,\n      \"finding\": \"Autophagy is impaired in Mybpc3 knock-in HCM mice (blunted autophagic flux, residual body and glycogen accumulation, increased Akt-mTORC1 signaling); rapamycin treatment or caloric restriction restores autophagic flux and partially rescues cardiomyopathy, establishing impaired autophagy as a pathomechanism in MYBPC3-mutant HCM.\",\n      \"method\": \"LC3-II protein levels, autophagic flux assay, Akt-mTORC1 signaling in KI mice and human HCM myectomies; rapamycin treatment; caloric restriction\",\n      \"journal\": \"Circulation. Heart failure\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — multiple markers plus pharmacological rescue, but mechanism linking cMyBP-C to mTORC1 not fully reconstituted\",\n      \"pmids\": [\"29021349\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2022,\n      \"finding\": \"MYBPC3 is expressed in cardiac fibroblasts (not only cardiomyocytes); CRISPR-mediated Mybpc3 disruption in fibroblasts activates NF-κB signaling, upregulates TGF-β1 and HIF-1α, enhances aerobic glycolysis, and accelerates fibroblast activation, contributing to myocardial fibrosis in HCM.\",\n      \"method\": \"CRISPR KO of Mybpc3 in NIH3T3 and cardiac fibroblasts; NF-κB signaling assays; TGF-β1, HIF-1α, glycolysis marker quantification; R495Q mutant pig model\",\n      \"journal\": \"Cell death & disease\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — multiple pathway assays in cell-based KO system plus in vivo pig model, but novel finding not yet replicated\",\n      \"pmids\": [\"36357371\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2021,\n      \"finding\": \"Among nontruncating MYBPC3 variants, approximately half of HCM-linked variants show alterations in RNA splicing or protein stability, both leading to cMyBP-C haploinsufficiency; these protein haploinsufficiency drivers associate with HCM pathogenicity with 100% and 94% specificity respectively.\",\n      \"method\": \"Minigene splicing assay; protein stability assays for 44 nontruncating MYBPC3 variants classified by cosegregation and population genetics\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — systematic cell-based functional testing of 44 variants with orthogonal splicing and stability assays\",\n      \"pmids\": [\"34097875\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2013,\n      \"finding\": \"AAV-mediated 5'-trans-splicing of Mybpc3 pre-mRNA in vivo produces full-length repaired cMyBP-C protein that incorporates correctly into the sarcomere; repaired mRNA reached up to 66% of total Mybpc3 transcripts in cultured cardiac myocytes.\",\n      \"method\": \"AAV-delivered pre-trans-splicing molecules in cultured cardiac myocytes and mouse hearts; immunoprecipitation; immunofluorescence for sarcomere incorporation\",\n      \"journal\": \"Molecular therapy. Nucleic acids\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — protein detection and sarcomere localization confirmed by immunoprecipitation and imaging\",\n      \"pmids\": [\"23820890\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2014,\n      \"finding\": \"Heterozygous MYBPC3 truncation mutation mice subjected to pressure overload (TAC) show haploinsufficiency (significantly reduced cMyBP-C at 4 weeks post-TAC), impaired force generation, higher Ca2+ sensitivity, blunted length-dependent activation, and greater hypertrophy than WT-TAC, establishing that stress-induced haploinsufficiency exacerbates dysfunction.\",\n      \"method\": \"Transverse aortic constriction in HET MYBPC3 truncation mice; myofilament force measurements; Ca2+ sensitivity; echocardiography; RNA sequencing\",\n      \"journal\": \"Journal of molecular and cellular cardiology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — in vivo stress model with myofilament functional readouts and protein quantification\",\n      \"pmids\": [\"25463273\"],\n      \"is_preprint\": false\n    }\n  ],\n  \"current_model\": \"cMyBP-C (encoded by MYBPC3) is a thick filament-associated regulatory protein that constrains myosin head proximity to actin through its N-terminal domains binding myosin S2; PKA and other kinases (CaMKII, PKC, PKD) phosphorylate specific serine residues (Ser273, Ser282, Ser302, Ser315) to relieve this constraint, increase cross-bridge cycling kinetics, and augment Ca2+-activated tension; the N-terminal domains also bind actin and shift tropomyosin position to modulate thin filament activation and damp spontaneous contractile oscillations; the C-terminal C10 domain anchors cMyBP-C to the myosin rod (LMM), and most HCM-causing truncating MYBPC3 mutations lead to NMD-mediated mRNA degradation and protein haploinsufficiency (reduced full-length cMyBP-C in myofilaments), which reciprocally augments myosin ATPase activity and reduces the super-relaxed myosin state, causing hypercontractility and impaired relaxation characteristic of HCM.\"\n}\n```","stage2_raw":"```json\n{\n  \"mechanistic_narrative\": \"MYBPC3 encodes cardiac myosin-binding protein C (cMyBP-C), a sarcomeric thick-filament regulatory protein that modulates cardiac contraction and relaxation by constraining myosin head proximity to actin and tuning thin-filament activation. The N-terminal domains (C0–C7) bind both the myosin S2 segment and F-actin, positioning tropomyosin to regulate Ca²⁺-dependent cross-bridge cycling, dampen spontaneous oscillatory contractions, and mediate myofilament Ca²⁺ sensitivity, while multi-site phosphorylation by PKA, CaMKII, PKC, and PKD at Ser273/Ser282/Ser302/Ser315 relieves the myosin head tether and differentially modulates contractile kinetics and tension [PMID:10024460, PMID:18599866, PMID:32078438, PMID:26718724, PMID:22636676, PMID:24606935]. The C-terminal C10 domain anchors cMyBP-C to the myosin rod (LMM), and disruption of this interaction abolishes sarcomeric incorporation [PMID:25583989]. MYBPC3 is the most commonly mutated gene in hypertrophic cardiomyopathy (HCM): truncating mutations undergo nonsense-mediated mRNA decay leading to protein haploinsufficiency that reciprocally augments myosin ATPase activity, reduces the super-relaxed myosin state, increases myofilament Ca²⁺ sensitivity, and impairs relaxation, while nontruncating pathogenic variants cause haploinsufficiency through defective splicing or accelerated protein degradation [PMID:19574547, PMID:30674652, PMID:15249187, PMID:34097875, PMID:32841044].\",\n  \"teleology\": [\n    {\n      \"year\": 1999,\n      \"claim\": \"Establishing the primary molecular interaction: the N-terminal regulatory domain of cMyBP-C binds the myosin S2 segment, and HCM mutations in S2 disrupt this interaction, providing the first direct biochemical basis for cMyBP-C's contractile regulatory function.\",\n      \"evidence\": \"In vitro binding assays with Kd measurements using recombinant cMyBP-C motif and myosin S2 fragments, plus localization in cardiomyocytes\",\n      \"pmids\": [\"10024460\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Whether the S2 interaction is the sole or primary mechanism of cross-bridge regulation was unclear\", \"In vivo relevance of the binding affinity not yet tested\", \"Phosphorylation effects on this interaction not assessed\"]\n    },\n    {\n      \"year\": 2004,\n      \"claim\": \"Genetic proof that cMyBP-C dose determines cardiac phenotype: heterozygous Mybpc3 knockout mice develop asymmetric septal hypertrophy resembling human HCM, while homozygous nulls show eccentric hypertrophy with diastolic dysfunction, establishing haploinsufficiency as sufficient for disease.\",\n      \"evidence\": \"Targeted deletion of Mybpc3 exons 1–2 in mice with echocardiographic, molecular, and morphological analysis at multiple ages\",\n      \"pmids\": [\"15249187\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Whether human MYBPC3 mutations act purely through haploinsufficiency or also via poison-peptide effects was not resolved\", \"Mechanism linking reduced cMyBP-C to hypertrophic signaling not identified\"]\n    },\n    {\n      \"year\": 2006,\n      \"claim\": \"cMyBP-C is required for normal in vivo contractile reserve: null mice lack the contractile enhancement normally elicited by β-adrenergic stimulation, showing cMyBP-C is essential for the adrenergic-mediated augmentation of cardiac function.\",\n      \"evidence\": \"Pressure-volume analysis and echocardiography in cMyBP-C null versus wild-type mice with β-adrenergic challenge and aortic banding\",\n      \"pmids\": [\"17122190\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Whether the deficit reflects loss of cMyBP-C phosphorylation specifically or a general structural disruption was unresolved\", \"Molecular basis of the blunted adrenergic response not dissected\"]\n    },\n    {\n      \"year\": 2008,\n      \"claim\": \"Structural evidence for the tether model: PKA phosphorylation of cMyBP-C displaces myosin heads radially toward actin, and this displacement is entirely absent in cMyBP-C null myocardium, directly demonstrating that cMyBP-C constrains myosin head position in a phosphorylation-dependent manner.\",\n      \"evidence\": \"Synchrotron low-angle X-ray diffraction of skinned trabeculae from wild-type and cMyBP-C null mice ± PKA\",\n      \"pmids\": [\"18599866\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Which phosphosites mediate the tether release was not resolved\", \"Contribution of thin-filament binding to the structural rearrangement not assessed\"]\n    },\n    {\n      \"year\": 2009,\n      \"claim\": \"Direct confirmation of haploinsufficiency in human HCM: no truncated cMyBP-C protein is detectable in myectomy tissue from patients with MYBPC3 truncation mutations, and total cMyBP-C is reduced to ~76% of normal, establishing that truncated transcripts are degraded rather than producing poison peptides.\",\n      \"evidence\": \"Immunoblotting and RT-PCR of human myectomy samples versus donor hearts across multiple MYBPC3 mutation types\",\n      \"pmids\": [\"19574547\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Whether the residual ~76% protein level is sufficient to prevent disease or represents an incomplete compensatory mechanism was unknown\", \"Mechanism of mRNA degradation (NMD) not directly demonstrated in these samples\"]\n    },\n    {\n      \"year\": 2011,\n      \"claim\": \"Dual binding target identified: cMyBP-C N-terminal domains bind F-actin subdomain 1, positioning them to shift tropomyosin and modulate thin-filament activation, revealing a second regulatory interface beyond myosin S2.\",\n      \"evidence\": \"Negative-stain EM and 3D helical reconstruction of F-actin decorated with N-terminal cMyBP-C fragments\",\n      \"pmids\": [\"21601575\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Functional consequence of actin binding on thin-filament activation kinetics not directly measured\", \"Relative contributions of actin versus S2 binding to contractile regulation unclear\"]\n    },\n    {\n      \"year\": 2012,\n      \"claim\": \"Increased myofilament Ca²⁺ sensitivity and diastolic dysfunction are primary consequences of MYBPC3 mutation, preceding and independent of hypertrophy, reframing these as initiating events rather than secondary consequences.\",\n      \"evidence\": \"Skinned trabeculae force measurements, intact myocyte Ca²⁺ transients, and echocardiography in pre-hypertrophic heterozygous and homozygous Mybpc3 knock-in mice\",\n      \"pmids\": [\"22465693\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Whether correcting Ca²⁺ sensitivity alone would prevent subsequent hypertrophy was not tested\", \"Specific molecular mechanism by which mutant cMyBP-C increases Ca²⁺ sensitivity not identified\"]\n    },\n    {\n      \"year\": 2012,\n      \"claim\": \"PKD phosphorylates cMyBP-C at Ser315 and requires cMyBP-C to augment maximal Ca²⁺-activated tension, expanding the kinase repertoire regulating cMyBP-C beyond PKA/CaMKII.\",\n      \"evidence\": \"Co-immunoprecipitation in contracting cardiomyocytes; force measurements in permeabilized WT versus cMyBP-C KO myocytes incubated with active PKD\",\n      \"pmids\": [\"22636676\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Physiological stimulus triggering PKD-cMyBP-C signaling in vivo not established\", \"Whether PKD phosphorylation of Ser315 alone is sufficient or requires cooperative phosphorylation at other sites\"]\n    },\n    {\n      \"year\": 2013,\n      \"claim\": \"The E258K missense mutation reveals how gain-of-function at the thin filament and loss-of-function at the thick filament converge: abolishing S2 interaction while increasing actin affinity accelerates contractile kinetics and reduces force, mechanistically linking HCM missense mutations to altered dual-binding properties.\",\n      \"evidence\": \"Yeast two-hybrid for S2 binding; force measurements in engineered cardiac tissue from cMyBP-C null mice reconstituted with WT or E258K cMyBP-C\",\n      \"pmids\": [\"23980194\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Whether other missense mutations show the same dual-binding alteration pattern was untested\", \"In vivo hemodynamic consequences not assessed\"]\n    },\n    {\n      \"year\": 2014,\n      \"claim\": \"Phosphosite hierarchy established: Ser282 non-phosphorylation combined with phosphomimetic substitutions at Ser273/302 (DAD variant) is detrimental, significantly reducing isometric tension and cross-bridge kinetics, demonstrating that site-specific phosphorylation patterns have opposing functional outcomes.\",\n      \"evidence\": \"Sinusoidal analysis in papillary fibers from cMyBP-C null mice expressing transgenic phosphosite-specific mutants (ADA, DAD, SAS)\",\n      \"pmids\": [\"24606935\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Whether this phosphorylation hierarchy exists in vivo under physiological signaling conditions was not demonstrated\", \"No structural explanation for why Ser282 state determines the functional outcome\"]\n    },\n    {\n      \"year\": 2015,\n      \"claim\": \"C10 domain integrity is essential for sarcomeric anchoring: the South Asian 25-bp deletion produces a C10 variant that cannot bind myosin LMM, fails to incorporate into sarcomeres, and causes contractile dysfunction, identifying a founder mutation mechanism.\",\n      \"evidence\": \"Adenoviral expression in adult rat cardiomyocytes; co-sedimentation, cross-linking, immunofluorescence, and subcellular fractionation\",\n      \"pmids\": [\"25583989\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Whether soluble mislocalized cMyBP-C has toxic gain-of-function effects was not addressed\", \"In vivo phenotype of this specific mutation in animal models not established\"]\n    },\n    {\n      \"year\": 2015,\n      \"claim\": \"HCM missense mutation L348P shifts tropomyosin to the open position on thin filaments beyond the effect of wild-type cMyBP-C, providing structural evidence that thin-filament activation by N-terminal domains is a gain-of-function mechanism in HCM.\",\n      \"evidence\": \"EM 3D reconstruction of thin filaments decorated with L348P versus WT and phosphorylated N-terminal cMyBP-C fragments\",\n      \"pmids\": [\"26718724\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Whether tropomyosin shift alone accounts for the Ca²⁺ sensitization phenotype not tested in intact sarcomeres\", \"How phosphorylation modulates the L348P gain-of-function not determined\"]\n    },\n    {\n      \"year\": 2019,\n      \"claim\": \"The unifying biophysical mechanism: cMyBP-C depletion shifts myosin from the super-relaxed (energy-conserving) state to a disordered-relaxed (ATP-hydrolyzing) state, and the myosin ATPase inhibitor MYK-461 rescues relaxation deficits, providing a pharmacological strategy targeting the downstream consequence of haploinsufficiency.\",\n      \"evidence\": \"Genetic and biochemical myosin conformation assays in mouse and human MYBPC3-mutant cardiomyocytes; pharmacological rescue with MYK-461\",\n      \"pmids\": [\"30674652\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Whether super-relaxed state reduction is the sole driver of hypercontractility or whether thin-filament effects contribute independently remains unresolved\", \"Long-term efficacy and safety of MYK-461 in MYBPC3 mutation carriers not established\"]\n    },\n    {\n      \"year\": 2019,\n      \"claim\": \"NMD as chronic stressor: premature termination codon mutations constitutively activate nonsense-mediated decay, and this chronic NMD activation—rather than haploinsufficiency alone—causes aberrant calcium handling; NMD inhibition normalizes calcium transients, revealing a non-sarcomeric pathogenic pathway.\",\n      \"evidence\": \"Isogenic iPSC-CMs from HCM patients; transcriptome analysis; pharmacological NMD inhibition with phenotype rescue\",\n      \"pmids\": [\"30586709\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Mechanism by which chronic NMD activation leads to calcium handling defects not identified\", \"Whether NMD inhibition is therapeutically viable in vivo unknown\"]\n    },\n    {\n      \"year\": 2020,\n      \"claim\": \"Acute reconstitution proves the N-terminal domains maintain sarcomeric stability: removal of C0–C7 from sarcomeres reduces Ca²⁺ sensitivity, speeds cross-bridge cycling, and triggers spontaneous oscillatory contractions; re-ligation rescues all phenotypes, establishing that cMyBP-C N-terminal domains actively damp contractile instability.\",\n      \"evidence\": \"TEVp cleavage and SpyCatcher/SpyTag re-ligation of N-terminal domains in permeabilized cardiomyocytes from gene-edited mice\",\n      \"pmids\": [\"32078438\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Whether SPOC occurs in intact myocardium with partial cMyBP-C depletion not tested\", \"The structural basis by which N-terminal domains suppress oscillations is unknown\"]\n    },\n    {\n      \"year\": 2020,\n      \"claim\": \"Protein-level compensation: heterozygous MYBPC3 frameshift mutations reduce WT mRNA but cardiomyocytes maintain near-normal cMyBP-C protein levels by decreasing degradation rate, revealing an innate post-translational buffering mechanism.\",\n      \"evidence\": \"Stable isotope labeling (SILAC) in patient and genome-engineered iPSC-CMs measuring synthesis and degradation rates\",\n      \"pmids\": [\"31877118\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Whether this compensatory mechanism fails under hemodynamic stress to produce haploinsufficiency in vivo is not resolved\", \"Molecular sensor/pathway controlling degradation rate adjustment unknown\"]\n    },\n    {\n      \"year\": 2020,\n      \"claim\": \"Domain-specific variant pathomechanisms: C10 missense variants fail to incorporate into myofilaments and degrade ~90% faster, while C3/C6 variants incorporate normally, demonstrating that nontruncating mutations cause loss-of-function through distinct domain-dependent mechanisms.\",\n      \"evidence\": \"Immunofluorescence and degradation rate measurements for mutant MyBP-C expressed in rat ventricular myocytes\",\n      \"pmids\": [\"32841044\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Functional consequence of incorporated C3/C6 variants on contractility not measured\", \"Whether C3/C6 variants that incorporate normally act through altered binding affinities not tested\"]\n    },\n    {\n      \"year\": 2021,\n      \"claim\": \"Systematic classification of nontruncating variants: ~50% of pathogenic missense/in-frame variants cause haploinsufficiency via RNA splicing defects or protein instability, with high specificity for pathogenicity, providing a functional framework for variant interpretation.\",\n      \"evidence\": \"Minigene splicing assays and protein stability assays for 44 nontruncating MYBPC3 variants correlated with cosegregation and population data\",\n      \"pmids\": [\"34097875\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"The other ~50% of pathogenic nontruncating variants presumably act through altered function rather than haploinsufficiency, but their mechanisms are uncharacterized\", \"Whether splicing and stability assays are sufficient for clinical variant classification not validated prospectively\"]\n    },\n    {\n      \"year\": null,\n      \"claim\": \"Key unresolved questions: (1) the structural basis of the cMyBP-C N-terminal interaction with both myosin S2 and actin simultaneously, and how phosphorylation switches between these binding modes at atomic resolution; (2) the molecular sensor that adjusts cMyBP-C degradation rate to compensate for haploinsufficiency; (3) whether thin-filament and thick-filament regulatory mechanisms of cMyBP-C are independently sufficient for disease or must converge; (4) the non-sarcomeric role of MYBPC3 in cardiac fibroblasts and its contribution to fibrosis in HCM.\",\n      \"evidence\": \"\",\n      \"pmids\": [],\n      \"confidence\": \"Low\",\n      \"gaps\": [\"No high-resolution structure of cMyBP-C N-terminal domains bound simultaneously to S2 and actin in the sarcomeric context\", \"Post-translational compensation pathway linking mRNA haploinsufficiency to reduced protein degradation unidentified\", \"Fibroblast role described in single study requiring independent replication\"]\n    }\n  ],\n  \"mechanism_profile\": {\n    \"molecular_activity\": [\n      {\"term_id\": \"GO:0008092\", \"supporting_discovery_ids\": [0, 4, 7, 14]},\n      {\"term_id\": \"GO:0005198\", \"supporting_discovery_ids\": [1, 8, 14]},\n      {\"term_id\": \"GO:0098772\", \"supporting_discovery_ids\": [1, 10, 14]}\n    ],\n    \"localization\": [\n      {\"term_id\": \"GO:0005856\", \"supporting_discovery_ids\": [0, 4, 8, 14]}\n    ],\n    \"pathway\": [\n      {\"term_id\": \"GO:0397014\", \"supporting_discovery_ids\": [1, 10, 14]},\n      {\"term_id\": \"R-HSA-162582\", \"supporting_discovery_ids\": [1, 12, 18]},\n      {\"term_id\": \"R-HSA-1643685\", \"supporting_discovery_ids\": [2, 3, 5, 10]}\n    ],\n    \"complexes\": [\n      \"sarcomeric A-band (C-zone thick filament)\"\n    ],\n    \"partners\": [\n      \"MYH7\",\n      \"ACTC1\",\n      \"TPM1\",\n      \"PRKD1\",\n      \"PRKACA\"\n    ],\n    \"other_free_text\": []\n  }\n}\n```"}