{"gene":"SCN5A","run_date":"2026-04-28T20:42:07","timeline":{"discoveries":[{"year":2006,"finding":"Nav1.5 C-terminus PDZ domain-binding motif (last three residues Ser-Ile-Val) associates with dystrophin via α- and β-syntrophin proteins; disruption of this motif abolishes the interaction. In dystrophin-deficient mdx5cv mice, Nav1.5 protein is reduced by 50% and sodium current is reduced by 29%, establishing that the dystrophin-syntrophin complex is required for proper expression and membrane function of Nav1.5.","method":"Pull-down with Nav1.5 C-terminus fusion proteins + mass spectrometry, Western blot, patch-clamp in isolated cardiomyocytes, ECG in mdx5cv mice","journal":"Circulation research","confidence":"High","confidence_rationale":"Tier 1-2 — multiple orthogonal methods (pulldown/MS, Western blot, patch-clamp, in vivo ECG) in a single rigorous study","pmids":["16857961"],"is_preprint":false},{"year":2002,"finding":"The SCN5A double mutant R1232W/T1620M associated with Brugada syndrome fails to traffic to the plasma membrane and is retained in the endoplasmic reticulum (co-localized with calnexin), resulting in abolition of functional sodium current. A positively charged residue at position 1232 (arginine or lysine) is required for proper transport of Nav1.5.","method":"Whole-cell patch clamp, immunofluorescence/confocal microscopy with FLAG-tagged constructs, site-directed mutagenesis in tsA201 cells","journal":"Circulation research","confidence":"High","confidence_rationale":"Tier 1 — reconstitution with mutagenesis and direct localization imaging in a single study","pmids":["11786529"],"is_preprint":false},{"year":2001,"finding":"Two SIDS-associated SCN5A missense mutations (A997S and R1826H) produce channels with slower current decay and a 2–3-fold increase in late (persistent) sodium current, establishing a gain-of-function arrhythmogenic mechanism for some SIDS cases.","method":"Mutagenesis, transient transfection in HEK cells, whole-cell patch clamp","journal":"JAMA","confidence":"High","confidence_rationale":"Tier 1 — in vitro electrophysiology with mutagenesis directly characterizing mechanistic current changes","pmids":["11710892"],"is_preprint":false},{"year":2003,"finding":"The common SCN5A polymorphism H558R in the I-II interdomain cytoplasmic linker can mitigate the in vitro loss-of-function effects of the nearby T512I mutation on sodium channel gating, demonstrating intragenic complementation between a polymorphism and a mutation on the same allele.","method":"Whole-cell patch clamp in heterologous expression, site-directed mutagenesis","journal":"The Journal of clinical investigation","confidence":"High","confidence_rationale":"Tier 1 — direct electrophysiological characterization with mutagenesis in two independent studies (also replicated by PMID 12454206)","pmids":["12569159"],"is_preprint":false},{"year":2003,"finding":"The common SCN5A polymorphism H558R rescues the trafficking defect and restores normal sodium current of the LQT3 mutation M1766L; M1766L alone causes ER retention and markedly reduced current, while M1766L on the H558R background shows normal surface trafficking and persistent late current, demonstrating intragenic complementation.","method":"Voltage clamp, immunocytochemistry for surface trafficking, site-directed mutagenesis in HEK cells","journal":"Physiological genomics","confidence":"High","confidence_rationale":"Tier 1 — mutagenesis, electrophysiology, and direct localization imaging in one study","pmids":["12454206"],"is_preprint":false},{"year":2005,"finding":"The Brugada-associated SCN5A mutation L325R produces misfolded Nav1.5 channels that can be partially rescued by mexiletine or curcumin; L325R channels also exert a dominant-negative effect on co-expressed wild-type channels, suggesting this mechanism underlies fever-exacerbated Brugada syndrome.","method":"Patch clamp at various temperatures, Western blot, co-expression experiments, cardiac action potential modeling in HEK293 cells","journal":"Cardiovascular research","confidence":"High","confidence_rationale":"Tier 1-2 — multiple orthogonal methods including pharmacological rescue, co-expression dominant-negative assay, and temperature-dependent kinetics","pmids":["15890323"],"is_preprint":false},{"year":2005,"finding":"The LQT3-associated SCN5A mutation L1825P is a misprocessed channel retained at the cell surface at only ~9% of wild-type levels; cisapride rescues surface expression to ~30% of wild-type while simultaneously increasing late sodium current, establishing a novel drug-induced arrhythmia mechanism via rescue of a trafficking-defective channel.","method":"Whole-cell patch clamp, confocal imaging with epitope-tagged constructs, cell-counting assays in CHO cells","journal":"Circulation","confidence":"High","confidence_rationale":"Tier 1-2 — electrophysiology plus direct surface-expression imaging with pharmacological rescue","pmids":["16301357"],"is_preprint":false},{"year":2004,"finding":"Transgenic mice expressing the LQT3 SCN5A mutation N1325S exhibit prolonged QT intervals, spontaneous polymorphic ventricular tachycardia and fibrillation, early afterdepolarizations, and a persistent late sodium current with slow recovery from inactivation; mexiletine suppresses these arrhythmias by blocking late INa and enhancing recovery from inactivation.","method":"Transgenic mouse model, in vivo ECG telemetry, patch clamp on isolated ventricular myocytes, pharmacological intervention with mexiletine","journal":"Cardiovascular research","confidence":"High","confidence_rationale":"Tier 1-2 — in vivo transgenic model combined with cellular electrophysiology and pharmacological rescue","pmids":["14736542"],"is_preprint":false},{"year":2011,"finding":"Nav1.5-dependent persistent Na+ influx (late INa) activates CaMKII, which in turn phosphorylates Nav1.5, further promoting Na+ influx in a positive feedback loop. CaMKII co-immunoprecipitates with Nav1.5, and knockdown of Nav1.5 (but not Nav1.1 or Nav1.2) prevents ATX-II-induced CaMKII phosphorylation.","method":"Co-immunoprecipitation, siRNA knockdown of specific Nav isoforms, CaMKII autophosphorylation assays, patch clamp, pharmacological inhibition in neonatal rat ventricular myocytes and N1325S transgenic mice","journal":"American journal of physiology. Cell physiology","confidence":"High","confidence_rationale":"Tier 1-2 — multiple orthogonal methods (Co-IP, isoform-specific knockdown, transgenic model, pharmacology) demonstrating bidirectional Nav1.5-CaMKII feedback","pmids":["21677263"],"is_preprint":false},{"year":2008,"finding":"Telethonin (encoded by TCAP) physically interacts with Nav1.5 (co-immunoprecipitation) and co-localizes with Nav1.5 in gastrointestinal smooth muscle. A telethonin mutation found in a patient with intestinal pseudo-obstruction doubles the Nav1.5 window current when co-expressed in HEK293 cells, identifying telethonin as a Nav1.5-interacting protein that modulates channel activation kinetics.","method":"Co-immunoprecipitation, immunolocalization, whole-cell patch clamp with co-expression in HEK293 cells","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 1-2 — Co-IP plus direct electrophysiological functional characterization with mutant co-expression","pmids":["18408010"],"is_preprint":false},{"year":2016,"finding":"The lateral-membrane MAGUK protein CASK directly interacts with the C-terminus of Nav1.5 (pull-down) and negatively regulates Nav1.5 surface expression specifically at the lateral membrane of cardiomyocytes. CASK silencing increases INa by enhancing Nav1.5 trafficking to the lateral membrane without affecting mRNA levels; this is prevented by the trafficking inhibitor brefeldin-A.","method":"Pull-down, whole-cell patch clamp, TIRF microscopy, biotinylation assays, in vivo siRNA knockdown, immunostaining in cardiac myocytes","journal":"Circulation research","confidence":"High","confidence_rationale":"Tier 1-2 — direct pulldown interaction plus multiple functional readouts (patch clamp, TIRF, biotinylation) in vitro and in vivo","pmids":["27364017"],"is_preprint":false},{"year":2014,"finding":"A cardiac enhancer located within the SCN10A locus (encompassing variant rs6801957) interacts with the SCN5A promoter and is essential for cardiac Scn5a expression; deletion of this enhancer in BAC transgenic mice abolishes Scn5a cardiac expression, and the rs6801957 variant modulates SCN5A transcript levels in human heart.","method":"High-resolution 4C-seq chromatin conformation analysis, BAC transgenic mouse enhancer deletion, qPCR of SCN5A transcript levels in human and mouse heart","journal":"The Journal of clinical investigation","confidence":"High","confidence_rationale":"Tier 1-2 — genome editing/deletion in vivo combined with chromatin conformation and expression quantification","pmids":["24642470"],"is_preprint":false},{"year":2012,"finding":"TBX5 directly drives Scn5a expression in the ventricular conduction system (VCS); deletion of Tbx5 from the mature murine VCS reduces Nav1.5 expression, causes loss of fast conduction, arrhythmias, and sudden death. A TBX5-responsive enhancer downstream of Scn5a, dependent on canonical T-box binding sites, drives VCS expression in vivo.","method":"Conditional Cre-mediated knockout in mice, ECG, in vivo enhancer reporter assay with T-box binding site mutagenesis, Western blot","journal":"The Journal of clinical investigation","confidence":"High","confidence_rationale":"Tier 1-2 — genetic KO with defined phenotype plus direct enhancer functional validation in vivo","pmids":["22728936"],"is_preprint":false},{"year":2013,"finding":"The cardiomyocyte molecular clock (BMAL1) controls circadian expression of Scn5a; inducible cardiomyocyte-specific Bmal1 deletion abolishes circadian Scn5a expression, reduces Nav1.5 protein and sodium current in ventricular myocytes, slows heart rate, prolongs QRS, and increases arrhythmia susceptibility. Overexpression of clock factors transactivates the Scn5a promoter in vitro.","method":"Inducible cardiomyocyte-specific Bmal1 KO mice, ECG telemetry, patch clamp, luciferase reporter assay, Western blot","journal":"American journal of physiology. Cell physiology","confidence":"High","confidence_rationale":"Tier 1-2 — conditional KO with multiple readouts plus in vitro promoter transactivation assay","pmids":["23364267"],"is_preprint":false},{"year":2019,"finding":"K219T-LMNA mutation causes increased binding of Lamin A/C to the SCN5A promoter, recruits the PRC2 component SUZ12, and deposits the repressive histone mark H3K27me3 at SCN5A, resulting in downregulation of Nav1.5 expression, reduced peak sodium current, and decreased conduction velocity in iPSC-derived cardiomyocytes. CRISPR/Cas9 correction of the mutation re-establishes sodium current density and SCN5A expression.","method":"iPSC-derived cardiomyocytes from K219T-LMNA patients, ChIP for Lamin A/C and H3K27me3 at SCN5A promoter, patch clamp, CRISPR/Cas9 correction","journal":"Nature communications","confidence":"High","confidence_rationale":"Tier 1-2 — ChIP, patch clamp, and CRISPR correction in human-derived cardiomyocytes provide strong mechanistic evidence","pmids":["31118417"],"is_preprint":false},{"year":2010,"finding":"Nav1.5 (encoded by SCN5A) is mechanosensitive: membrane stretch produces graded hyperpolarizing shifts in both activation and inactivation V1/2 (~0.7 mV/mmHg), increases peak current by recruiting more active channels, and slows recovery from inactivation. Stretch accelerates voltage sensor movement but not gate opening or fast inactivation rate constants.","method":"Whole-cell and cell-attached patch clamp in HEK293 cells expressing Nav1.5, application of graded patch pressure","journal":"The Journal of physiology","confidence":"High","confidence_rationale":"Tier 1 — direct in vitro electrophysiological characterization with mechanistic kinetic analysis","pmids":["21041530"],"is_preprint":false},{"year":2012,"finding":"Foxo1 transcription factor directly binds insulin-responsive elements (IRE: 5'-CAAAACA-3') in the SCN5A promoter (confirmed by ChIP), and negatively regulates Nav1.5 expression; constitutively nuclear Foxo1 reduces Nav1.5 expression and INa, while Foxo1 siRNA increases Nav1.5 expression. H2O2 suppresses Nav1.5 expression by promoting Foxo1 nuclear localization, and this suppression is prevented by Foxo1 siRNA.","method":"ChIP, luciferase reporter assay, constitutively nuclear Foxo1 overexpression, RNAi knockdown, whole-cell voltage clamp in HL-1 cardiomyocytes","journal":"PloS one","confidence":"High","confidence_rationale":"Tier 1-2 — ChIP directly demonstrates Foxo1 occupancy at SCN5A promoter; functional effects confirmed by multiple orthogonal approaches","pmids":["22400069"],"is_preprint":false},{"year":2016,"finding":"H2O2-activated Wnt/β-catenin signaling suppresses Nav1.5 expression; nuclear β-catenin interacts with TCF4 and both are recruited to the SCN5A promoter (ChIP), reducing its transcriptional activity. GSK-3β inhibitors phenocopy H2O2 suppression, and β-catenin siRNA prevents H2O2-mediated reduction of SCN5A promoter activity and Nav1.5 expression.","method":"Co-immunoprecipitation, ChIP, luciferase SCN5A promoter assay, GSK-3β pharmacological manipulation, siRNA, immunofluorescence, patch clamp in HL-1 cells","journal":"Free radical biology & medicine","confidence":"High","confidence_rationale":"Tier 1-2 — ChIP demonstrating direct promoter recruitment combined with multiple functional assays","pmids":["27068063"],"is_preprint":false},{"year":2016,"finding":"GATA4 and GATA5 co-occupy the SCN5A promoter and first intron in human left ventricle (ChIP/Re-ChIP); GATA4 and GATA5 synergistically activate the SCN5A promoter in a GATA binding-site-dependent manner. GATA4 mRNA levels are strongly and positively correlated with SCN5A transcript levels in human heart.","method":"ChIP, sequential Re-ChIP, luciferase reporter assay with promoter mutagenesis, ddPCR in fresh human left ventricle samples","journal":"Journal of molecular and cellular cardiology","confidence":"High","confidence_rationale":"Tier 1-2 — direct ChIP in native human cardiac tissue plus functional reporter assays","pmids":["27894866"],"is_preprint":false},{"year":2019,"finding":"An evolutionarily conserved enhancer cluster downstream of SCN5A (within the SCN5A-SCN10A locus) controls the chromatin conformation of a >0.5 Mb genomic region and is selectively required for cardiac Scn5a expression, normal cardiac conduction, and normal embryonic development; genome editing deletions of individual enhancer components in mice demonstrate this requirement.","method":"Genome editing (CRISPR-based deletions) in mice, cardiac Scn5a expression analysis, ECG conduction analysis","journal":"Nature communications","confidence":"High","confidence_rationale":"Tier 1-2 — in vivo genome editing with multiple deletion alleles and functional validation","pmids":["31666509"],"is_preprint":false},{"year":2018,"finding":"miR-24 potently suppresses SCN5A expression post-transcriptionally; a synonymous SNP (rs1805126) adjacent to the miR-24 binding site in the SCN5A coding sequence modulates this suppression. In mice, decreased Scn5a expression leads to accumulation of myocardial reactive oxygen species.","method":"miRNA reporter assays, human cardiac expression analysis linked to SNP genotype, mouse model with reduced Scn5a expression and ROS measurement","journal":"The Journal of clinical investigation","confidence":"High","confidence_rationale":"Tier 2 — functional miRNA binding assay, human expression data, and in vivo mouse phenotyping","pmids":["29457789"],"is_preprint":false},{"year":2018,"finding":"HuR (ELAVL1) binds to and stabilizes SCN5A mRNA in cardiomyocytes; HuR is downregulated in failing hearts, and AAV9-mediated overexpression of HuR in mice after MI increases SCN5A expression, improves action potential upstroke and conduction velocity in the infarct border zone, and reduces reentrant arrhythmia risk.","method":"RNA-binding protein immunoprecipitation (RIP), AAV9 overexpression in mice post-MI, optical mapping of intact hearts, qRT-PCR","journal":"Heart rhythm","confidence":"High","confidence_rationale":"Tier 2 — RIP demonstrates direct SCN5A mRNA binding; in vivo AAV rescue with optical mapping provides functional validation","pmids":["29454929"],"is_preprint":false},{"year":2021,"finding":"FAT10 binds to lysine residues in the C-terminal fragments of Nav1.5 (co-immunoprecipitation) and prevents Nav1.5 ubiquitination by the E3 ligase Nedd4-2, thereby stabilizing Nav1.5 membrane expression. Cardiac-specific Fat10 knockout mice show reduced peak INa, augmented late INa, decreased Nav1.5 membrane expression, and increased ventricular arrhythmia/mortality after MI.","method":"Co-immunoprecipitation, conditional cardiac KO mice (Myh6-Cre × Fat10F/F), patch clamp, Western blot, immunofluorescence, ubiquitination assays","journal":"Cell death & disease","confidence":"High","confidence_rationale":"Tier 1-2 — Co-IP demonstrating direct binding, ubiquitination assay, and KO mouse with defined electrophysiological phenotype","pmids":["33414395"],"is_preprint":false},{"year":2018,"finding":"BrS-associated Nav1.5 mutations with ER trafficking defects fail to positively modulate Kir2.1/2.2 channels, thus reducing IK1 in addition to INa; Golgi trafficking-defective Nav1.5 mutants additionally exert a dominant-negative effect on Kir2.1/2.2. ER trafficking-defective Nav1.5 channels can be partially rescued by Kir2.1/2.2 through an unconventional GRASP-dependent secretory route.","method":"Overexpression of mutant Nav1.5 in expression systems, rat ventricular cardiomyocytes and hiPSC-CMs; SCN5A haploinsufficient mouse model; patch clamp; co-expression experiments","journal":"JCI insight","confidence":"High","confidence_rationale":"Tier 2 — multiple models (cell lines, rat cardiomyocytes, hiPSC-CMs, mouse model) with direct electrophysiological readouts","pmids":["30232268"],"is_preprint":false},{"year":2022,"finding":"Most SCN5A missense loss-of-function variants exert a dominant-negative effect on co-expressed wild-type Nav1.5 (32 of 35 complete LoF variants), reducing peak current below 75% of wild-type alone; individuals carrying dominant-negative LoF variants have a 2.7-fold higher Brugada syndrome burden versus putative haploinsufficient variants.","method":"Automated patch clamp in HEK293T cells with heterozygous co-expression of WT and mutant SCN5A; clinical database comparison","journal":"Genetics in medicine","confidence":"High","confidence_rationale":"Tier 1-2 — systematic electrophysiological characterization of 50 variants with direct dominant-negative co-expression assay, replicated across large variant set","pmids":["35305865"],"is_preprint":false},{"year":2014,"finding":"The SCN5A E558X nonsense mutation (modeled at orthologous position in pig) causes conduction abnormalities and increased susceptibility to ventricular fibrillation initiated by short-coupled ventricular premature beats; optical mapping during VF shows organized focal activity arising from the right ventricular free wall, establishing a large-animal mechanistic model of sodium channelopathy arrhythmia.","method":"Knock-in pig model (SCN5A E558X/+), in vivo ECG, Langendorff-perfused heart pacing, optical mapping during VF","journal":"The Journal of clinical investigation","confidence":"High","confidence_rationale":"Tier 2 — large-animal genetic model with optical mapping providing direct mechanistic arrhythmia substrate data","pmids":["25500882"],"is_preprint":false},{"year":2003,"finding":"The LQT3 SCN5A mutation L619F in the domain I-II linker increases maintained (late) sodium current, shifts steady-state inactivation by +5.8 mV without shifting activation, and increases window current; this establishes a role for the I-II cytoplasmic linker in Nav1.5 inactivation gating.","method":"Whole-cell patch clamp in transiently transfected HEK cells, site-directed mutagenesis","journal":"Human mutation","confidence":"High","confidence_rationale":"Tier 1 — in vitro electrophysiology with mutagenesis directly revealing domain I-II linker function in inactivation","pmids":["12673799"],"is_preprint":false},{"year":2003,"finding":"The LQT3 SCN5A mutation I1768V (domain IVS6 C-terminal end) destabilizes the inactivated state: mutant channels recover from inactivation 2.4-fold faster and show less slow inactivation than wild-type, without persistent late current, demonstrating a role for domain IVS6 in stabilizing Nav1.5 inactivation.","method":"Two-electrode voltage clamp in Xenopus oocytes after cRNA injection, site-directed mutagenesis","journal":"Cardiovascular research","confidence":"High","confidence_rationale":"Tier 1 — direct in vitro electrophysiology with mutagenesis in Xenopus oocyte reconstitution system","pmids":["12650885"],"is_preprint":false},{"year":2008,"finding":"The M1875T gain-of-function SCN5A mutation associated with familial atrial fibrillation causes a +16.4 mV shift in steady-state inactivation V1/2 (increasing channel availability) without persistent late current; this is mechanistically distinct from LQT3 and is predicted to increase atrial excitability.","method":"Whole-cell patch clamp in HEK cells expressing M1875T Nav1.5","journal":"Journal of the American College of Cardiology","confidence":"High","confidence_rationale":"Tier 1 — direct in vitro electrophysiology with mutagenesis characterizing the gain-of-function mechanism","pmids":["18929244"],"is_preprint":false},{"year":2022,"finding":"TBX5 variants (p.F206L and p.D111Y) differentially regulate Nav1.5: p.F206L fails to transactivate the SCN5A promoter reducing peak INa and causing Brugada syndrome phenotype; p.D111Y increases SCN5A expression but fails to repress CAMK2D and SPTBN4, causing increased CaMKIIδ and βIV-spectrin and thereby augmenting late INa (INaL), prolonging action potential duration and causing LQT syndrome phenotype.","method":"Luciferase reporter, hiPSC-CMs, HL-1 cells, mouse cardiomyocytes overexpressing Tbx5 variants, patch clamp, ranolazine pharmacology, ECG in transgenic mice","journal":"Cardiovascular research","confidence":"High","confidence_rationale":"Tier 1-2 — multiple orthogonal systems (hiPSC-CMs, mouse model, cell lines) with molecular and electrophysiological validation","pmids":["33576403"],"is_preprint":false},{"year":2002,"finding":"Nav1.5 protein is expressed in the mouse brain, co-localizing with neurofilaments and clustering at high density in neuronal axons, suggesting a role in CNS electrical signal propagation.","method":"Immunohistochemistry with Nav1.5-specific antibody in mouse brain sections, co-localization with neurofilament markers","journal":"Neuroreport","confidence":"Medium","confidence_rationale":"Tier 3 — single immunolocalization study without functional validation of the CNS role","pmids":["12499865"],"is_preprint":false},{"year":2006,"finding":"Canine intracardiac neurons functionally express Nav1.5 (TTX-resistant sodium current with IC50 ~1.17 µM for TTX, inactivation kinetics consistent with Nav1.5); SCN5A expression confirmed by PCR and sequencing, suggesting intrinsic cardiac ganglia as a site of SCN5A function relevant to autonomically modulated arrhythmias.","method":"Patch clamp of dissociated intracardiac neurons, immunohistochemistry, RT-PCR with sequencing","journal":"Heart rhythm","confidence":"Medium","confidence_rationale":"Tier 2 — electrophysiology combined with molecular identification, but functional consequence in arrhythmia context not directly demonstrated","pmids":["16818219"],"is_preprint":false},{"year":2015,"finding":"Nav1.5 (SCN5A) promotes breast cancer tumor growth and metastatic dissemination in vivo; stable Nav1.5 knockdown reduces tumor growth, local invasion, and liver/lung/spleen metastasis in an orthotopic model, increases apoptosis, and reduces CD44 expression, suggesting Nav1.5 activity regulates invasion via the CD44-src-cortactin axis.","method":"Stable shRNA knockdown of Nav1.5, orthotopic breast cancer xenograft model, TTX-blocked patch clamp in tumor slices confirming functional VGSC activity in vivo","journal":"Oncotarget","confidence":"Medium","confidence_rationale":"Tier 2 — in vivo KD with defined metastatic phenotype plus functional current confirmation in tumor tissue, but pathway placement is partial","pmids":["26452220"],"is_preprint":false},{"year":2014,"finding":"Human macrophage SCN5A initiates an innate immune signaling pathway: pharmacological channel stimulation or cytoplasmic poly(I:C) (dsRNA mimic) activates the channel, leading to ADCY8 (adenylate cyclase 8) and ATF2-mediated transcription of SP100-related genes and interferon β. Intracellular poly(I:C) augments inward voltage-sensitive sodium current and inhibits outward nonselective current.","method":"Pharmacological channel activation, electrophysiology (whole-cell and intracellular poly(I:C) application), gene expression analysis in human macrophages","journal":"The Journal of biological chemistry","confidence":"Medium","confidence_rationale":"Tier 2 — direct electrophysiological and signaling measurements in native macrophages, but mechanistic pathway validation is partial","pmids":["25368329"],"is_preprint":false},{"year":2024,"finding":"Anti-Nav1.5 autoantibodies are present in 90% of Brugada syndrome patients (vs. 6% controls); these autoantibodies significantly reduce sodium current density in cellular models, and injection of BrS patient plasma induces Brugada-like ECG abnormalities in wild-type mice, establishing an immunopathogenic mechanism for BrS independent of SCN5A mutation.","method":"Western blot, immunoprecipitation, immunofluorescence screening; patch clamp in HEK293A cells; in vivo plasma injection in wild-type mice with ECG monitoring","journal":"European heart journal","confidence":"High","confidence_rationale":"Tier 1-2 — direct electrophysiological confirmation of reduced INa by autoantibodies plus in vivo mouse plasma injection phenocopy experiment","pmids":["39078224"],"is_preprint":false},{"year":2011,"finding":"The SCN5A-S1103Y African American common polymorphism interacts with the SCN5A-R680H mutation to significantly increase late INa (3.4-fold when co-expressed, 3.6-fold on the same construct) in the major Q1077del splice variant background; intracellular acidosis (pH 6.7) further amplifies this interaction, providing a mechanistic basis for arrhythmic sudden death.","method":"Whole-cell patch clamp in HEK293 cells with site-directed mutagenesis; splice-variant-specific expression constructs; intracellular pH manipulation","journal":"Physiological genomics","confidence":"High","confidence_rationale":"Tier 1 — rigorous electrophysiology demonstrating splice-variant and polymorphism context-dependent late INa amplification","pmids":["21385947"],"is_preprint":false}],"current_model":"SCN5A encodes Nav1.5, the principal cardiac voltage-gated sodium channel α-subunit responsible for the rapid depolarization upstroke of the action potential; its expression is transcriptionally regulated by TBX5, GATA4/5, BMAL1/molecular clock, Foxo1, and Wnt/β-catenin signaling, and post-transcriptionally by miR-24 and the mRNA-stabilizing protein HuR, while its membrane trafficking and function are controlled by a multiprotein complex involving dystrophin/syntrophins, CASK (at lateral membranes), and FAT10 (preventing Nedd4-2-mediated ubiquitination/degradation); gain-of-function mutations produce increased late INa causing LQT3 and atrial fibrillation via CaMKII-Nav1.5 positive feedback, while loss-of-function mutations—many acting via dominant-negative mechanisms or ER/Golgi trafficking defects—cause Brugada syndrome, conduction disease, and sick sinus syndrome, with channel mechanosensitivity, an intronic SCN10A enhancer, and anti-Nav1.5 autoantibodies representing additional regulatory and pathogenic mechanisms."},"narrative":{"teleology":[{"year":2001,"claim":"Establishing that SCN5A gain-of-function mutations increase persistent late INa provided the first mechanistic link between Nav1.5 dysfunction and lethal arrhythmia (SIDS), showing that even modest increases in late current are pathogenic.","evidence":"Patch clamp of A997S and R1826H mutant channels in HEK cells showing 2–3-fold increased late INa","pmids":["11710892"],"confidence":"High","gaps":["Cellular context limited to heterologous expression; no cardiomyocyte or in vivo validation at that time"]},{"year":2002,"claim":"Demonstrating that BrS-associated mutations cause ER retention of Nav1.5 established protein trafficking failure as a distinct loss-of-function mechanism, separate from gating defects.","evidence":"Confocal imaging showing calnexin co-localization of R1232W/T1620M Nav1.5 and abolished INa in tsA201 cells","pmids":["11786529"],"confidence":"High","gaps":["Whether trafficking-defective mutants also exert dominant-negative effects on wild-type channels was not tested"]},{"year":2003,"claim":"Discovery that the common H558R polymorphism rescues nearby loss-of-function mutations (T512I, M1766L) through intragenic complementation revealed that SCN5A genotype-phenotype relationships depend on cis-allelic context and modifier polymorphisms.","evidence":"Patch clamp and immunocytochemistry of single and double mutant constructs in HEK cells","pmids":["12569159","12454206"],"confidence":"High","gaps":["Whether intragenic rescue occurs in native cardiomyocytes with endogenous accessory subunits was not tested","Structural basis for complementation unknown"]},{"year":2003,"claim":"Electrophysiological characterization of mutations in domain I–II linker (L619F) and domain IVS6 (I1768V) mapped distinct structural contributions to Nav1.5 inactivation gating—the linker controlling steady-state inactivation and IVS6 stabilizing the inactivated state.","evidence":"Patch clamp with site-directed mutagenesis in HEK cells and Xenopus oocytes","pmids":["12673799","12650885"],"confidence":"High","gaps":["No structural data to explain how these residues interact with the inactivation gate at atomic resolution"]},{"year":2004,"claim":"A transgenic mouse expressing LQT3 mutation N1325S recapitulated human QT prolongation, spontaneous ventricular arrhythmias, and early afterdepolarizations in vivo, validating the late-INa gain-of-function mechanism and demonstrating mexiletine as a targeted therapy.","evidence":"In vivo ECG telemetry, patch clamp on isolated ventricular myocytes, mexiletine pharmacological rescue in transgenic mice","pmids":["14736542"],"confidence":"High","gaps":["Single mutation model; generalizability to other LQT3 mutations not established"]},{"year":2005,"claim":"Demonstration that the BrS mutation L325R exerts a dominant-negative effect on co-expressed wild-type Nav1.5, with fever exacerbation, introduced dominant-negative suppression as a key pathomechanism beyond simple haploinsufficiency.","evidence":"Co-expression patch clamp at varying temperatures, pharmacological rescue with mexiletine/curcumin in HEK293 cells","pmids":["15890323","16301357"],"confidence":"High","gaps":["Generality of dominant-negative mechanism across BrS variants not yet established at that time"]},{"year":2006,"claim":"Identification of the dystrophin–syntrophin complex as a required scaffold for Nav1.5 membrane expression established that cardiac sodium current depends on cytoskeletal anchoring at the channel C-terminus.","evidence":"Pull-down/mass spectrometry, patch clamp, and ECG in dystrophin-deficient mdx5cv mice showing 50% reduction in Nav1.5 and 29% reduction in INa","pmids":["16857961"],"confidence":"High","gaps":["Whether dystrophin loss preferentially affects lateral versus intercalated disc Nav1.5 pools was not resolved"]},{"year":2008,"claim":"The M1875T mutation linked to familial atrial fibrillation revealed a gain-of-function mechanism (+16.4 mV inactivation shift increasing channel availability) distinct from LQT3 persistent current, showing that different biophysical defects in the same channel produce chamber-specific arrhythmias.","evidence":"Patch clamp in HEK cells expressing M1875T Nav1.5","pmids":["18929244"],"confidence":"High","gaps":["Why the atrium is preferentially affected over the ventricle was not mechanistically explained"]},{"year":2010,"claim":"Nav1.5 was shown to be intrinsically mechanosensitive, with membrane stretch shifting activation and inactivation voltage dependence and increasing peak current, providing a biophysical basis for stretch-induced arrhythmias.","evidence":"Whole-cell and cell-attached patch clamp with graded pressure application in HEK293 cells","pmids":["21041530"],"confidence":"High","gaps":["Whether mechanosensitivity is modulated by accessory subunits or cytoskeletal anchoring in cardiomyocytes was not tested"]},{"year":2011,"claim":"Discovery of a CaMKII–Nav1.5 positive-feedback loop (late INa activates CaMKII, which phosphorylates Nav1.5 to further increase late INa) provided a molecular amplification mechanism for arrhythmogenesis in LQT3.","evidence":"Co-immunoprecipitation, isoform-specific siRNA, CaMKII phosphorylation assays in neonatal rat ventricular myocytes and N1325S transgenic mice","pmids":["21677263"],"confidence":"High","gaps":["Specific CaMKII phosphorylation sites on Nav1.5 responsible for current augmentation not mapped in this study","Whether the feedback loop operates similarly in human cardiomyocytes was not shown"]},{"year":2012,"claim":"Conditional knockout of Tbx5 from the murine ventricular conduction system identified TBX5 as a direct transcriptional activator of Scn5a via a VCS-specific enhancer, establishing the first transcription factor–Nav1.5 regulatory axis essential for fast conduction and survival.","evidence":"Cre-mediated VCS-specific Tbx5 KO in mice, in vivo enhancer-reporter assay with T-box site mutagenesis","pmids":["22728936"],"confidence":"High","gaps":["Whether TBX5 is sufficient to restore Nav1.5 in diseased conduction tissue was not tested"]},{"year":2012,"claim":"Foxo1 was identified as a direct transcriptional repressor of SCN5A via insulin-responsive elements in its promoter, linking metabolic and oxidative stress signaling to sodium current regulation.","evidence":"ChIP showing Foxo1 occupancy at SCN5A promoter, luciferase reporter, constitutively nuclear Foxo1 and RNAi in HL-1 cardiomyocytes","pmids":["22400069"],"confidence":"High","gaps":["In vivo cardiac-specific Foxo1 manipulation not performed"]},{"year":2013,"claim":"Demonstration that BMAL1 controls circadian Scn5a expression in cardiomyocytes, with its deletion reducing Nav1.5 and increasing arrhythmia susceptibility, established a molecular clock–cardiac conduction axis.","evidence":"Inducible cardiomyocyte-specific Bmal1 KO mice with ECG telemetry, patch clamp, and promoter transactivation assay","pmids":["23364267"],"confidence":"High","gaps":["Whether other clock components independently regulate SCN5A or act solely through BMAL1 was not dissected"]},{"year":2014,"claim":"Identification and deletion of a cardiac enhancer within SCN10A that physically contacts the SCN5A promoter (via 4C-seq) and is required for cardiac Scn5a expression resolved how non-coding GWAS variants at SCN10A influence cardiac conduction through long-range regulation of SCN5A.","evidence":"4C-seq chromatin conformation, BAC transgenic enhancer deletion, qPCR in human and mouse heart","pmids":["24642470"],"confidence":"High","gaps":["The transcription factors mediating enhancer–promoter communication at this locus were not fully identified"]},{"year":2016,"claim":"Multiple transcriptional regulators converging on the SCN5A promoter were characterized: GATA4/GATA5 synergistically activate SCN5A via direct co-occupancy in human ventricle; Wnt/β-catenin–TCF4 represses SCN5A under oxidative stress; and CASK negatively regulates Nav1.5 lateral-membrane trafficking.","evidence":"ChIP/Re-ChIP in human heart for GATA4/5; ChIP for β-catenin/TCF4 with siRNA in HL-1 cells; pull-down, TIRF, biotinylation, and in vivo siRNA for CASK in cardiomyocytes","pmids":["27894866","27068063","27364017"],"confidence":"High","gaps":["How CASK versus dystrophin–syntrophin complexes coordinately partition Nav1.5 between lateral membrane and intercalated disc is incompletely understood"]},{"year":2018,"claim":"Post-transcriptional regulation of SCN5A was defined: miR-24 suppresses SCN5A via a coding-region target modulated by a synonymous SNP, and HuR stabilizes SCN5A mRNA with therapeutic potential demonstrated by AAV9-HuR overexpression improving conduction and reducing arrhythmias post-MI.","evidence":"miRNA reporter assays and human expression quantitative analysis for miR-24; RIP and AAV9-HuR overexpression with optical mapping post-MI in mice for HuR","pmids":["29457789","29454929"],"confidence":"High","gaps":["Whether miR-24 and HuR act on the same mRNA pool or in distinct subcellular compartments is unknown"]},{"year":2018,"claim":"BrS-associated Nav1.5 trafficking mutants were shown to additionally impair Kir2.1/2.2 channel function, revealing that Nav1.5 positively modulates IK1 and that trafficking defects reduce both INa and IK1, compounding loss of excitability.","evidence":"Co-expression in cell lines, rat cardiomyocytes, hiPSC-CMs, and SCN5A haploinsufficient mice; patch clamp","pmids":["30232268"],"confidence":"High","gaps":["The molecular interface between Nav1.5 and Kir2.x that mediates positive modulation is not structurally defined"]},{"year":2019,"claim":"K219T-LMNA was shown to epigenetically silence SCN5A by recruiting PRC2 (SUZ12) and depositing H3K27me3 at its promoter, establishing a laminopathy-driven mechanism for sodium channel downregulation correctable by CRISPR/Cas9.","evidence":"ChIP for Lamin A/C and H3K27me3 at SCN5A promoter, patch clamp, and CRISPR correction in K219T-LMNA iPSC-CMs","pmids":["31118417"],"confidence":"High","gaps":["Whether other LMNA mutations use the same PRC2-dependent mechanism to suppress SCN5A is not established"]},{"year":2019,"claim":"Genome editing of a conserved enhancer cluster downstream of SCN5A confirmed that multiple enhancer elements within the SCN5A–SCN10A locus cooperatively control chromatin architecture over >0.5 Mb and are selectively required for cardiac Scn5a expression and normal conduction.","evidence":"CRISPR-based enhancer deletions in mice with cardiac expression and ECG analysis","pmids":["31666509"],"confidence":"High","gaps":["How the individual enhancers communicate with each other and with the SCN5A promoter in 3D chromatin space is incompletely resolved"]},{"year":2021,"claim":"FAT10 was identified as a novel Nav1.5 stabilizer that prevents Nedd4-2-mediated ubiquitination by binding Nav1.5 C-terminal lysines, with cardiac-specific Fat10 KO reducing peak INa and increasing arrhythmia susceptibility post-MI.","evidence":"Co-IP, ubiquitination assays, conditional cardiac Fat10 KO mice with patch clamp and post-MI arrhythmia phenotyping","pmids":["33414395"],"confidence":"High","gaps":["Whether FAT10 competes with ubiquitin at specific lysines or blocks Nedd4-2 access allosterically is unresolved"]},{"year":2022,"claim":"Systematic co-expression of 50 SCN5A loss-of-function variants with wild-type showed that dominant-negative effects (not haploinsufficiency) are the predominant mechanism for most BrS-associated missense mutations, with a 2.7-fold higher disease burden for dominant-negative variants, redefining the genetic architecture of Brugada syndrome.","evidence":"Automated patch clamp with heterozygous WT + mutant co-expression in HEK293T cells; clinical BrS burden comparison","pmids":["35305865"],"confidence":"High","gaps":["Structural mechanism by which mutant subunits poison wild-type channel complexes is not resolved"]},{"year":2022,"claim":"TBX5 variants were shown to cause either BrS (via failure to activate SCN5A promoter) or LQTS (via failure to repress CaMKIIδ/βIV-spectrin, augmenting late INa), demonstrating that a single upstream transcription factor can produce opposing arrhythmia syndromes through distinct transcriptional targets.","evidence":"Luciferase reporter, hiPSC-CMs, HL-1 cells, mouse cardiomyocytes, patch clamp, ranolazine pharmacology","pmids":["33576403"],"confidence":"High","gaps":["Complete set of TBX5 direct targets relevant to cardiac electrophysiology not defined"]},{"year":2024,"claim":"Anti-Nav1.5 autoantibodies were identified in 90% of BrS patients, and injection of patient plasma into wild-type mice reproduced BrS-like ECG changes, establishing a mutation-independent autoimmune pathogenic mechanism.","evidence":"Western blot/IP screening of patient sera, patch clamp in HEK293A cells treated with patient IgG, in vivo plasma injection in WT mice with ECG","pmids":["39078224"],"confidence":"High","gaps":["Epitope(s) recognized by the autoantibodies on Nav1.5 not mapped","Whether autoantibodies are pathogenic drivers or secondary phenomena in BrS requires longitudinal studies"]},{"year":null,"claim":"Key unresolved questions include: the high-resolution structural basis for dominant-negative poisoning of WT by mutant Nav1.5 subunits; the mechanism by which Nav1.5 positively modulates Kir2.x channels; how intercalated disc versus lateral membrane Nav1.5 pools are differentially regulated; and whether anti-Nav1.5 autoantibodies are primary drivers or secondary markers in Brugada syndrome.","evidence":"","pmids":[],"confidence":"Low","gaps":["No cryo-EM structure of full-length human Nav1.5 in complex with trafficking partners or mutant subunits","Molecular interface for Nav1.5–Kir2.x interaction undefined","Relative contributions of autoimmune versus genetic mechanisms in genotype-negative BrS unknown"]}],"mechanism_profile":{"molecular_activity":[{"term_id":"GO:0005215","term_label":"transporter activity","supporting_discovery_ids":[2,7,15,24,28]},{"term_id":"GO:0140299","term_label":"molecular sensor activity","supporting_discovery_ids":[15]}],"localization":[{"term_id":"GO:0005886","term_label":"plasma membrane","supporting_discovery_ids":[0,1,6,10,22]},{"term_id":"GO:0005783","term_label":"endoplasmic reticulum","supporting_discovery_ids":[1,4]}],"pathway":[{"term_id":"R-HSA-112316","term_label":"Neuronal System","supporting_discovery_ids":[2,7,15,24,28]},{"term_id":"R-HSA-382551","term_label":"Transport of small molecules","supporting_discovery_ids":[2,7,15,24]},{"term_id":"R-HSA-74160","term_label":"Gene expression (Transcription)","supporting_discovery_ids":[11,12,13,16,17,18]},{"term_id":"R-HSA-162582","term_label":"Signal Transduction","supporting_discovery_ids":[8,17]},{"term_id":"R-HSA-9609507","term_label":"Protein localization","supporting_discovery_ids":[1,6,10,22,23]},{"term_id":"R-HSA-1643685","term_label":"Disease","supporting_discovery_ids":[2,5,24,34]}],"complexes":["Dystrophin-syntrophin complex"],"partners":["SNTA1","SNTB1","DMD","CASK","UBD","CAMK2D","TCAP","ELAVL1"],"other_free_text":[]},"mechanistic_narrative":"SCN5A encodes Nav1.5, the principal voltage-gated sodium channel α-subunit of the heart, responsible for the rapid depolarization upstroke of the cardiac action potential and essential for normal impulse conduction. Cardiac SCN5A expression is transcriptionally controlled by TBX5, GATA4/GATA5, BMAL1 (circadian clock), Foxo1, and Wnt/β-catenin signaling acting on its promoter and a critical intronic enhancer within the SCN10A locus, while post-transcriptionally it is suppressed by miR-24 and stabilized by the RNA-binding protein HuR [PMID:22728936, PMID:27894866, PMID:23364267, PMID:22400069, PMID:27068063, PMID:24642470, PMID:29457789, PMID:29454929]. Nav1.5 membrane density is regulated by a dystrophin–syntrophin complex at the C-terminus, lateral-membrane CASK-dependent trafficking, and FAT10-mediated protection from Nedd4-2 ubiquitination, while gain-of-function mutations that increase persistent late sodium current (INa) cause long QT syndrome type 3 and atrial fibrillation—amplified by a CaMKII–Nav1.5 positive-feedback loop—and loss-of-function mutations, most of which act through dominant-negative suppression of co-expressed wild-type channels or ER/Golgi trafficking defects, cause Brugada syndrome, cardiac conduction disease, and sudden infant death syndrome [PMID:16857961, PMID:27364017, PMID:33414395, PMID:14736542, PMID:35305865, PMID:11786529, PMID:21677263, PMID:11710892, PMID:18929244]. An autoimmune mechanism involving anti-Nav1.5 autoantibodies that reduce sodium current density and reproduce Brugada-type ECG changes in vivo represents an additional, mutation-independent pathogenic pathway [PMID:39078224]."},"prefetch_data":{"uniprot":{"accession":"Q14524","full_name":"Sodium channel protein type 5 subunit alpha","aliases":["Sodium channel protein cardiac muscle subunit alpha","Sodium channel protein type V subunit alpha","Voltage-gated sodium channel subunit alpha Nav1.5","hH1"],"length_aa":2016,"mass_kda":226.9,"function":"Pore-forming subunit of Nav1.5, a voltage-gated sodium (Nav) channel that directly mediates the depolarizing phase of action potentials in excitable membranes. Navs, also called VGSCs (voltage-gated sodium channels) or VDSCs (voltage-dependent sodium channels), operate by switching between closed and open conformations depending on the voltage difference across the membrane. In the open conformation they allow Na(+) ions to selectively pass through the pore, along their electrochemical gradient. The influx of Na(+) ions provokes membrane depolarization, initiating the propagation of electrical signals throughout cells and tissues (PubMed:1309946, PubMed:21447824, PubMed:23085483, PubMed:23420830, PubMed:25370050, PubMed:26279430, PubMed:26392562, PubMed:26776555). Nav1.5 is the predominant sodium channel expressed in myocardial cells and it is responsible for the initial upstroke of the action potential in cardiac myocytes, thereby initiating the heartbeat (PubMed:11234013, PubMed:11804990, PubMed:12569159, PubMed:1309946). Required for normal electrical conduction including formation of the infranodal ventricular conduction system and normal action potential configuration, as a result of its interaction with XIRP2 (By similarity)","subcellular_location":"Cell membrane; Cytoplasm, perinuclear region; Cell membrane, sarcolemma, T-tubule; Cell junction","url":"https://www.uniprot.org/uniprotkb/Q14524/entry"},"depmap":{"release":"DepMap","has_data":true,"is_common_essential":false,"resolved_as":"","url":"https://depmap.org/portal/gene/SCN5A","classification":"Not Classified","n_dependent_lines":4,"n_total_lines":1208,"dependency_fraction":0.0033112582781456954},"opencell":{"profiled":false,"resolved_as":"","ensg_id":"","cell_line_id":"","localizations":[],"interactors":[],"url":"https://opencell.sf.czbiohub.org/search/SCN5A","total_profiled":1310},"omim":[{"mim_id":"621529","title":"TRANSMEMBRANE PROTEIN 168; TMEM168","url":"https://www.omim.org/entry/621529"},{"mim_id":"616249","title":"LONG QT SYNDROME 15; LQT15","url":"https://www.omim.org/entry/616249"},{"mim_id":"616247","title":"LONG QT SYNDROME 14; LQT14","url":"https://www.omim.org/entry/616247"},{"mim_id":"615396","title":"LEFT VENTRICULAR NONCOMPACTION 10; LVNC10","url":"https://www.omim.org/entry/615396"},{"mim_id":"615378","title":"ATRIAL FIBRILLATION, FAMILIAL, 14; ATFB14","url":"https://www.omim.org/entry/615378"}],"hpa":{"profiled":true,"resolved_as":"","reliability":"Supported","locations":[{"location":"Plasma membrane","reliability":"Supported"},{"location":"Nucleoplasm","reliability":"Additional"},{"location":"Nucleoli","reliability":"Additional"}],"tissue_specificity":"Tissue enriched","tissue_distribution":"Detected in some","driving_tissues":[{"tissue":"heart muscle","ntpm":49.7}],"url":"https://www.proteinatlas.org/search/SCN5A"},"hgnc":{"alias_symbol":["Nav1.5","LQT3","HB1","HBBD","PFHB1","IVF","HB2","HH1","SSS1","CDCD2","CMPD2","ICCD"],"prev_symbol":["CMD1E"]},"alphafold":{"accession":"Q14524","domains":[{"cath_id":"1.20.120.350","chopping":"19-36_56-240","consensus_level":"medium","plddt":78.4854,"start":19,"end":240},{"cath_id":"1.20.120.350","chopping":"1171-1309","consensus_level":"medium","plddt":82.1878,"start":1171,"end":1309},{"cath_id":"-","chopping":"1362-1398","consensus_level":"medium","plddt":79.8895,"start":1362,"end":1398},{"cath_id":"1.20.120.350","chopping":"1510-1549_1556-1641","consensus_level":"medium","plddt":81.3883,"start":1510,"end":1641},{"cath_id":"1.10.287,1.20.1440","chopping":"1642-1781","consensus_level":"medium","plddt":82.8552,"start":1642,"end":1781},{"cath_id":"1.10.238.10","chopping":"1785-1903","consensus_level":"medium","plddt":74.3493,"start":1785,"end":1903}],"viewer_url":"https://alphafold.ebi.ac.uk/entry/Q14524","model_url":"https://alphafold.ebi.ac.uk/files/AF-Q14524-F1-model_v6.cif","pae_url":"https://alphafold.ebi.ac.uk/files/AF-Q14524-F1-predicted_aligned_error_v6.png","plddt_mean":67.25},"mouse_models":{"mgi_url":"https://www.informatics.jax.org/marker/summary?nomen=SCN5A","jax_strain_url":"https://www.jax.org/strain/search?query=SCN5A"},"sequence":{"accession":"Q14524","fasta_url":"https://rest.uniprot.org/uniprotkb/Q14524.fasta","uniprot_url":"https://www.uniprot.org/uniprotkb/Q14524/entry","alphafold_viewer_url":"https://alphafold.ebi.ac.uk/entry/Q14524"}},"corpus_meta":[{"pmid":"10973849","id":"PMC_10973849","title":"Spectrum of mutations in long-QT syndrome genes. KVLQT1, HERG, SCN5A, KCNE1, and KCNE2.","date":"2000","source":"Circulation","url":"https://pubmed.ncbi.nlm.nih.gov/10973849","citation_count":961,"is_preprint":false},{"pmid":"15466643","id":"PMC_15466643","title":"SCN5A mutation associated with dilated cardiomyopathy, conduction disorder, and arrhythmia.","date":"2004","source":"Circulation","url":"https://pubmed.ncbi.nlm.nih.gov/15466643","citation_count":346,"is_preprint":false},{"pmid":"11710892","id":"PMC_11710892","title":"Postmortem molecular analysis of SCN5A defects in sudden infant death syndrome.","date":"2001","source":"JAMA","url":"https://pubmed.ncbi.nlm.nih.gov/11710892","citation_count":319,"is_preprint":false},{"pmid":"10716483","id":"PMC_10716483","title":"Differential effects of beta-adrenergic agonists and antagonists in LQT1, LQT2 and LQT3 models of the long QT syndrome.","date":"2000","source":"Journal of the American College of Cardiology","url":"https://pubmed.ncbi.nlm.nih.gov/10716483","citation_count":305,"is_preprint":false},{"pmid":"29798782","id":"PMC_29798782","title":"Clinical Spectrum of SCN5A Mutations: Long QT Syndrome, Brugada Syndrome, and Cardiomyopathy.","date":"2018","source":"JACC. 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Nav1.5.","date":"2016","source":"Biochimica et biophysica acta","url":"https://pubmed.ncbi.nlm.nih.gov/26907222","citation_count":16,"is_preprint":false},{"pmid":"25923670","id":"PMC_25923670","title":"Arrhythmogenic Biophysical Phenotype for SCN5A Mutation S1787N Depends upon Splice Variant Background and Intracellular Acidosis.","date":"2015","source":"PloS one","url":"https://pubmed.ncbi.nlm.nih.gov/25923670","citation_count":16,"is_preprint":false},{"pmid":"37369559","id":"PMC_37369559","title":"Beneficial effects of chronic mexiletine treatment in a human model of SCN5A overlap syndrome.","date":"2023","source":"Europace : European pacing, arrhythmias, and cardiac electrophysiology : journal of the working groups on cardiac pacing, arrhythmias, and cardiac cellular electrophysiology of the European Society of Cardiology","url":"https://pubmed.ncbi.nlm.nih.gov/37369559","citation_count":16,"is_preprint":false},{"pmid":"18033008","id":"PMC_18033008","title":"Cardiac sodium channel Nav1.5 and its associated proteins.","date":"2007","source":"Archives des maladies du coeur et des vaisseaux","url":"https://pubmed.ncbi.nlm.nih.gov/18033008","citation_count":15,"is_preprint":false},{"pmid":"39078224","id":"PMC_39078224","title":"NaV1.5 autoantibodies in Brugada syndrome: pathogenetic implications.","date":"2024","source":"European heart journal","url":"https://pubmed.ncbi.nlm.nih.gov/39078224","citation_count":15,"is_preprint":false}],"cost":{"stage1":{"model":"claude-sonnet-4-6","input_tokens":51874,"output_tokens":8945,"usd":0.144899},"stage2":{"model":"claude-opus-4-6","input_tokens":12785,"output_tokens":5462,"usd":0.300712},"total_usd":0.445611,"stage1_batch_id":"msgbatch_011rkcQdVV1RaFq9XhcG6df6","stage2_batch_id":"msgbatch_01RzgrJafdF4EWHhj5mNi6dh","note":"batch pricing = 50% of standard"},"stage1_raw":"```json\n{\n  \"discoveries\": [\n    {\n      \"year\": 2006,\n      \"finding\": \"Nav1.5 C-terminus PDZ domain-binding motif (last three residues Ser-Ile-Val) associates with dystrophin via α- and β-syntrophin proteins; disruption of this motif abolishes the interaction. In dystrophin-deficient mdx5cv mice, Nav1.5 protein is reduced by 50% and sodium current is reduced by 29%, establishing that the dystrophin-syntrophin complex is required for proper expression and membrane function of Nav1.5.\",\n      \"method\": \"Pull-down with Nav1.5 C-terminus fusion proteins + mass spectrometry, Western blot, patch-clamp in isolated cardiomyocytes, ECG in mdx5cv mice\",\n      \"journal\": \"Circulation research\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1-2 — multiple orthogonal methods (pulldown/MS, Western blot, patch-clamp, in vivo ECG) in a single rigorous study\",\n      \"pmids\": [\"16857961\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2002,\n      \"finding\": \"The SCN5A double mutant R1232W/T1620M associated with Brugada syndrome fails to traffic to the plasma membrane and is retained in the endoplasmic reticulum (co-localized with calnexin), resulting in abolition of functional sodium current. A positively charged residue at position 1232 (arginine or lysine) is required for proper transport of Nav1.5.\",\n      \"method\": \"Whole-cell patch clamp, immunofluorescence/confocal microscopy with FLAG-tagged constructs, site-directed mutagenesis in tsA201 cells\",\n      \"journal\": \"Circulation research\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — reconstitution with mutagenesis and direct localization imaging in a single study\",\n      \"pmids\": [\"11786529\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2001,\n      \"finding\": \"Two SIDS-associated SCN5A missense mutations (A997S and R1826H) produce channels with slower current decay and a 2–3-fold increase in late (persistent) sodium current, establishing a gain-of-function arrhythmogenic mechanism for some SIDS cases.\",\n      \"method\": \"Mutagenesis, transient transfection in HEK cells, whole-cell patch clamp\",\n      \"journal\": \"JAMA\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — in vitro electrophysiology with mutagenesis directly characterizing mechanistic current changes\",\n      \"pmids\": [\"11710892\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2003,\n      \"finding\": \"The common SCN5A polymorphism H558R in the I-II interdomain cytoplasmic linker can mitigate the in vitro loss-of-function effects of the nearby T512I mutation on sodium channel gating, demonstrating intragenic complementation between a polymorphism and a mutation on the same allele.\",\n      \"method\": \"Whole-cell patch clamp in heterologous expression, site-directed mutagenesis\",\n      \"journal\": \"The Journal of clinical investigation\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — direct electrophysiological characterization with mutagenesis in two independent studies (also replicated by PMID 12454206)\",\n      \"pmids\": [\"12569159\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2003,\n      \"finding\": \"The common SCN5A polymorphism H558R rescues the trafficking defect and restores normal sodium current of the LQT3 mutation M1766L; M1766L alone causes ER retention and markedly reduced current, while M1766L on the H558R background shows normal surface trafficking and persistent late current, demonstrating intragenic complementation.\",\n      \"method\": \"Voltage clamp, immunocytochemistry for surface trafficking, site-directed mutagenesis in HEK cells\",\n      \"journal\": \"Physiological genomics\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — mutagenesis, electrophysiology, and direct localization imaging in one study\",\n      \"pmids\": [\"12454206\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2005,\n      \"finding\": \"The Brugada-associated SCN5A mutation L325R produces misfolded Nav1.5 channels that can be partially rescued by mexiletine or curcumin; L325R channels also exert a dominant-negative effect on co-expressed wild-type channels, suggesting this mechanism underlies fever-exacerbated Brugada syndrome.\",\n      \"method\": \"Patch clamp at various temperatures, Western blot, co-expression experiments, cardiac action potential modeling in HEK293 cells\",\n      \"journal\": \"Cardiovascular research\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1-2 — multiple orthogonal methods including pharmacological rescue, co-expression dominant-negative assay, and temperature-dependent kinetics\",\n      \"pmids\": [\"15890323\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2005,\n      \"finding\": \"The LQT3-associated SCN5A mutation L1825P is a misprocessed channel retained at the cell surface at only ~9% of wild-type levels; cisapride rescues surface expression to ~30% of wild-type while simultaneously increasing late sodium current, establishing a novel drug-induced arrhythmia mechanism via rescue of a trafficking-defective channel.\",\n      \"method\": \"Whole-cell patch clamp, confocal imaging with epitope-tagged constructs, cell-counting assays in CHO cells\",\n      \"journal\": \"Circulation\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1-2 — electrophysiology plus direct surface-expression imaging with pharmacological rescue\",\n      \"pmids\": [\"16301357\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2004,\n      \"finding\": \"Transgenic mice expressing the LQT3 SCN5A mutation N1325S exhibit prolonged QT intervals, spontaneous polymorphic ventricular tachycardia and fibrillation, early afterdepolarizations, and a persistent late sodium current with slow recovery from inactivation; mexiletine suppresses these arrhythmias by blocking late INa and enhancing recovery from inactivation.\",\n      \"method\": \"Transgenic mouse model, in vivo ECG telemetry, patch clamp on isolated ventricular myocytes, pharmacological intervention with mexiletine\",\n      \"journal\": \"Cardiovascular research\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1-2 — in vivo transgenic model combined with cellular electrophysiology and pharmacological rescue\",\n      \"pmids\": [\"14736542\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2011,\n      \"finding\": \"Nav1.5-dependent persistent Na+ influx (late INa) activates CaMKII, which in turn phosphorylates Nav1.5, further promoting Na+ influx in a positive feedback loop. CaMKII co-immunoprecipitates with Nav1.5, and knockdown of Nav1.5 (but not Nav1.1 or Nav1.2) prevents ATX-II-induced CaMKII phosphorylation.\",\n      \"method\": \"Co-immunoprecipitation, siRNA knockdown of specific Nav isoforms, CaMKII autophosphorylation assays, patch clamp, pharmacological inhibition in neonatal rat ventricular myocytes and N1325S transgenic mice\",\n      \"journal\": \"American journal of physiology. Cell physiology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1-2 — multiple orthogonal methods (Co-IP, isoform-specific knockdown, transgenic model, pharmacology) demonstrating bidirectional Nav1.5-CaMKII feedback\",\n      \"pmids\": [\"21677263\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2008,\n      \"finding\": \"Telethonin (encoded by TCAP) physically interacts with Nav1.5 (co-immunoprecipitation) and co-localizes with Nav1.5 in gastrointestinal smooth muscle. A telethonin mutation found in a patient with intestinal pseudo-obstruction doubles the Nav1.5 window current when co-expressed in HEK293 cells, identifying telethonin as a Nav1.5-interacting protein that modulates channel activation kinetics.\",\n      \"method\": \"Co-immunoprecipitation, immunolocalization, whole-cell patch clamp with co-expression in HEK293 cells\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1-2 — Co-IP plus direct electrophysiological functional characterization with mutant co-expression\",\n      \"pmids\": [\"18408010\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2016,\n      \"finding\": \"The lateral-membrane MAGUK protein CASK directly interacts with the C-terminus of Nav1.5 (pull-down) and negatively regulates Nav1.5 surface expression specifically at the lateral membrane of cardiomyocytes. CASK silencing increases INa by enhancing Nav1.5 trafficking to the lateral membrane without affecting mRNA levels; this is prevented by the trafficking inhibitor brefeldin-A.\",\n      \"method\": \"Pull-down, whole-cell patch clamp, TIRF microscopy, biotinylation assays, in vivo siRNA knockdown, immunostaining in cardiac myocytes\",\n      \"journal\": \"Circulation research\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1-2 — direct pulldown interaction plus multiple functional readouts (patch clamp, TIRF, biotinylation) in vitro and in vivo\",\n      \"pmids\": [\"27364017\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2014,\n      \"finding\": \"A cardiac enhancer located within the SCN10A locus (encompassing variant rs6801957) interacts with the SCN5A promoter and is essential for cardiac Scn5a expression; deletion of this enhancer in BAC transgenic mice abolishes Scn5a cardiac expression, and the rs6801957 variant modulates SCN5A transcript levels in human heart.\",\n      \"method\": \"High-resolution 4C-seq chromatin conformation analysis, BAC transgenic mouse enhancer deletion, qPCR of SCN5A transcript levels in human and mouse heart\",\n      \"journal\": \"The Journal of clinical investigation\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1-2 — genome editing/deletion in vivo combined with chromatin conformation and expression quantification\",\n      \"pmids\": [\"24642470\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2012,\n      \"finding\": \"TBX5 directly drives Scn5a expression in the ventricular conduction system (VCS); deletion of Tbx5 from the mature murine VCS reduces Nav1.5 expression, causes loss of fast conduction, arrhythmias, and sudden death. A TBX5-responsive enhancer downstream of Scn5a, dependent on canonical T-box binding sites, drives VCS expression in vivo.\",\n      \"method\": \"Conditional Cre-mediated knockout in mice, ECG, in vivo enhancer reporter assay with T-box binding site mutagenesis, Western blot\",\n      \"journal\": \"The Journal of clinical investigation\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1-2 — genetic KO with defined phenotype plus direct enhancer functional validation in vivo\",\n      \"pmids\": [\"22728936\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2013,\n      \"finding\": \"The cardiomyocyte molecular clock (BMAL1) controls circadian expression of Scn5a; inducible cardiomyocyte-specific Bmal1 deletion abolishes circadian Scn5a expression, reduces Nav1.5 protein and sodium current in ventricular myocytes, slows heart rate, prolongs QRS, and increases arrhythmia susceptibility. Overexpression of clock factors transactivates the Scn5a promoter in vitro.\",\n      \"method\": \"Inducible cardiomyocyte-specific Bmal1 KO mice, ECG telemetry, patch clamp, luciferase reporter assay, Western blot\",\n      \"journal\": \"American journal of physiology. Cell physiology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1-2 — conditional KO with multiple readouts plus in vitro promoter transactivation assay\",\n      \"pmids\": [\"23364267\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2019,\n      \"finding\": \"K219T-LMNA mutation causes increased binding of Lamin A/C to the SCN5A promoter, recruits the PRC2 component SUZ12, and deposits the repressive histone mark H3K27me3 at SCN5A, resulting in downregulation of Nav1.5 expression, reduced peak sodium current, and decreased conduction velocity in iPSC-derived cardiomyocytes. CRISPR/Cas9 correction of the mutation re-establishes sodium current density and SCN5A expression.\",\n      \"method\": \"iPSC-derived cardiomyocytes from K219T-LMNA patients, ChIP for Lamin A/C and H3K27me3 at SCN5A promoter, patch clamp, CRISPR/Cas9 correction\",\n      \"journal\": \"Nature communications\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1-2 — ChIP, patch clamp, and CRISPR correction in human-derived cardiomyocytes provide strong mechanistic evidence\",\n      \"pmids\": [\"31118417\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2010,\n      \"finding\": \"Nav1.5 (encoded by SCN5A) is mechanosensitive: membrane stretch produces graded hyperpolarizing shifts in both activation and inactivation V1/2 (~0.7 mV/mmHg), increases peak current by recruiting more active channels, and slows recovery from inactivation. Stretch accelerates voltage sensor movement but not gate opening or fast inactivation rate constants.\",\n      \"method\": \"Whole-cell and cell-attached patch clamp in HEK293 cells expressing Nav1.5, application of graded patch pressure\",\n      \"journal\": \"The Journal of physiology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — direct in vitro electrophysiological characterization with mechanistic kinetic analysis\",\n      \"pmids\": [\"21041530\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2012,\n      \"finding\": \"Foxo1 transcription factor directly binds insulin-responsive elements (IRE: 5'-CAAAACA-3') in the SCN5A promoter (confirmed by ChIP), and negatively regulates Nav1.5 expression; constitutively nuclear Foxo1 reduces Nav1.5 expression and INa, while Foxo1 siRNA increases Nav1.5 expression. H2O2 suppresses Nav1.5 expression by promoting Foxo1 nuclear localization, and this suppression is prevented by Foxo1 siRNA.\",\n      \"method\": \"ChIP, luciferase reporter assay, constitutively nuclear Foxo1 overexpression, RNAi knockdown, whole-cell voltage clamp in HL-1 cardiomyocytes\",\n      \"journal\": \"PloS one\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1-2 — ChIP directly demonstrates Foxo1 occupancy at SCN5A promoter; functional effects confirmed by multiple orthogonal approaches\",\n      \"pmids\": [\"22400069\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2016,\n      \"finding\": \"H2O2-activated Wnt/β-catenin signaling suppresses Nav1.5 expression; nuclear β-catenin interacts with TCF4 and both are recruited to the SCN5A promoter (ChIP), reducing its transcriptional activity. GSK-3β inhibitors phenocopy H2O2 suppression, and β-catenin siRNA prevents H2O2-mediated reduction of SCN5A promoter activity and Nav1.5 expression.\",\n      \"method\": \"Co-immunoprecipitation, ChIP, luciferase SCN5A promoter assay, GSK-3β pharmacological manipulation, siRNA, immunofluorescence, patch clamp in HL-1 cells\",\n      \"journal\": \"Free radical biology & medicine\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1-2 — ChIP demonstrating direct promoter recruitment combined with multiple functional assays\",\n      \"pmids\": [\"27068063\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2016,\n      \"finding\": \"GATA4 and GATA5 co-occupy the SCN5A promoter and first intron in human left ventricle (ChIP/Re-ChIP); GATA4 and GATA5 synergistically activate the SCN5A promoter in a GATA binding-site-dependent manner. GATA4 mRNA levels are strongly and positively correlated with SCN5A transcript levels in human heart.\",\n      \"method\": \"ChIP, sequential Re-ChIP, luciferase reporter assay with promoter mutagenesis, ddPCR in fresh human left ventricle samples\",\n      \"journal\": \"Journal of molecular and cellular cardiology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1-2 — direct ChIP in native human cardiac tissue plus functional reporter assays\",\n      \"pmids\": [\"27894866\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2019,\n      \"finding\": \"An evolutionarily conserved enhancer cluster downstream of SCN5A (within the SCN5A-SCN10A locus) controls the chromatin conformation of a >0.5 Mb genomic region and is selectively required for cardiac Scn5a expression, normal cardiac conduction, and normal embryonic development; genome editing deletions of individual enhancer components in mice demonstrate this requirement.\",\n      \"method\": \"Genome editing (CRISPR-based deletions) in mice, cardiac Scn5a expression analysis, ECG conduction analysis\",\n      \"journal\": \"Nature communications\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1-2 — in vivo genome editing with multiple deletion alleles and functional validation\",\n      \"pmids\": [\"31666509\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2018,\n      \"finding\": \"miR-24 potently suppresses SCN5A expression post-transcriptionally; a synonymous SNP (rs1805126) adjacent to the miR-24 binding site in the SCN5A coding sequence modulates this suppression. In mice, decreased Scn5a expression leads to accumulation of myocardial reactive oxygen species.\",\n      \"method\": \"miRNA reporter assays, human cardiac expression analysis linked to SNP genotype, mouse model with reduced Scn5a expression and ROS measurement\",\n      \"journal\": \"The Journal of clinical investigation\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — functional miRNA binding assay, human expression data, and in vivo mouse phenotyping\",\n      \"pmids\": [\"29457789\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2018,\n      \"finding\": \"HuR (ELAVL1) binds to and stabilizes SCN5A mRNA in cardiomyocytes; HuR is downregulated in failing hearts, and AAV9-mediated overexpression of HuR in mice after MI increases SCN5A expression, improves action potential upstroke and conduction velocity in the infarct border zone, and reduces reentrant arrhythmia risk.\",\n      \"method\": \"RNA-binding protein immunoprecipitation (RIP), AAV9 overexpression in mice post-MI, optical mapping of intact hearts, qRT-PCR\",\n      \"journal\": \"Heart rhythm\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — RIP demonstrates direct SCN5A mRNA binding; in vivo AAV rescue with optical mapping provides functional validation\",\n      \"pmids\": [\"29454929\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2021,\n      \"finding\": \"FAT10 binds to lysine residues in the C-terminal fragments of Nav1.5 (co-immunoprecipitation) and prevents Nav1.5 ubiquitination by the E3 ligase Nedd4-2, thereby stabilizing Nav1.5 membrane expression. Cardiac-specific Fat10 knockout mice show reduced peak INa, augmented late INa, decreased Nav1.5 membrane expression, and increased ventricular arrhythmia/mortality after MI.\",\n      \"method\": \"Co-immunoprecipitation, conditional cardiac KO mice (Myh6-Cre × Fat10F/F), patch clamp, Western blot, immunofluorescence, ubiquitination assays\",\n      \"journal\": \"Cell death & disease\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1-2 — Co-IP demonstrating direct binding, ubiquitination assay, and KO mouse with defined electrophysiological phenotype\",\n      \"pmids\": [\"33414395\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2018,\n      \"finding\": \"BrS-associated Nav1.5 mutations with ER trafficking defects fail to positively modulate Kir2.1/2.2 channels, thus reducing IK1 in addition to INa; Golgi trafficking-defective Nav1.5 mutants additionally exert a dominant-negative effect on Kir2.1/2.2. ER trafficking-defective Nav1.5 channels can be partially rescued by Kir2.1/2.2 through an unconventional GRASP-dependent secretory route.\",\n      \"method\": \"Overexpression of mutant Nav1.5 in expression systems, rat ventricular cardiomyocytes and hiPSC-CMs; SCN5A haploinsufficient mouse model; patch clamp; co-expression experiments\",\n      \"journal\": \"JCI insight\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — multiple models (cell lines, rat cardiomyocytes, hiPSC-CMs, mouse model) with direct electrophysiological readouts\",\n      \"pmids\": [\"30232268\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2022,\n      \"finding\": \"Most SCN5A missense loss-of-function variants exert a dominant-negative effect on co-expressed wild-type Nav1.5 (32 of 35 complete LoF variants), reducing peak current below 75% of wild-type alone; individuals carrying dominant-negative LoF variants have a 2.7-fold higher Brugada syndrome burden versus putative haploinsufficient variants.\",\n      \"method\": \"Automated patch clamp in HEK293T cells with heterozygous co-expression of WT and mutant SCN5A; clinical database comparison\",\n      \"journal\": \"Genetics in medicine\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1-2 — systematic electrophysiological characterization of 50 variants with direct dominant-negative co-expression assay, replicated across large variant set\",\n      \"pmids\": [\"35305865\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2014,\n      \"finding\": \"The SCN5A E558X nonsense mutation (modeled at orthologous position in pig) causes conduction abnormalities and increased susceptibility to ventricular fibrillation initiated by short-coupled ventricular premature beats; optical mapping during VF shows organized focal activity arising from the right ventricular free wall, establishing a large-animal mechanistic model of sodium channelopathy arrhythmia.\",\n      \"method\": \"Knock-in pig model (SCN5A E558X/+), in vivo ECG, Langendorff-perfused heart pacing, optical mapping during VF\",\n      \"journal\": \"The Journal of clinical investigation\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — large-animal genetic model with optical mapping providing direct mechanistic arrhythmia substrate data\",\n      \"pmids\": [\"25500882\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2003,\n      \"finding\": \"The LQT3 SCN5A mutation L619F in the domain I-II linker increases maintained (late) sodium current, shifts steady-state inactivation by +5.8 mV without shifting activation, and increases window current; this establishes a role for the I-II cytoplasmic linker in Nav1.5 inactivation gating.\",\n      \"method\": \"Whole-cell patch clamp in transiently transfected HEK cells, site-directed mutagenesis\",\n      \"journal\": \"Human mutation\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — in vitro electrophysiology with mutagenesis directly revealing domain I-II linker function in inactivation\",\n      \"pmids\": [\"12673799\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2003,\n      \"finding\": \"The LQT3 SCN5A mutation I1768V (domain IVS6 C-terminal end) destabilizes the inactivated state: mutant channels recover from inactivation 2.4-fold faster and show less slow inactivation than wild-type, without persistent late current, demonstrating a role for domain IVS6 in stabilizing Nav1.5 inactivation.\",\n      \"method\": \"Two-electrode voltage clamp in Xenopus oocytes after cRNA injection, site-directed mutagenesis\",\n      \"journal\": \"Cardiovascular research\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — direct in vitro electrophysiology with mutagenesis in Xenopus oocyte reconstitution system\",\n      \"pmids\": [\"12650885\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2008,\n      \"finding\": \"The M1875T gain-of-function SCN5A mutation associated with familial atrial fibrillation causes a +16.4 mV shift in steady-state inactivation V1/2 (increasing channel availability) without persistent late current; this is mechanistically distinct from LQT3 and is predicted to increase atrial excitability.\",\n      \"method\": \"Whole-cell patch clamp in HEK cells expressing M1875T Nav1.5\",\n      \"journal\": \"Journal of the American College of Cardiology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — direct in vitro electrophysiology with mutagenesis characterizing the gain-of-function mechanism\",\n      \"pmids\": [\"18929244\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2022,\n      \"finding\": \"TBX5 variants (p.F206L and p.D111Y) differentially regulate Nav1.5: p.F206L fails to transactivate the SCN5A promoter reducing peak INa and causing Brugada syndrome phenotype; p.D111Y increases SCN5A expression but fails to repress CAMK2D and SPTBN4, causing increased CaMKIIδ and βIV-spectrin and thereby augmenting late INa (INaL), prolonging action potential duration and causing LQT syndrome phenotype.\",\n      \"method\": \"Luciferase reporter, hiPSC-CMs, HL-1 cells, mouse cardiomyocytes overexpressing Tbx5 variants, patch clamp, ranolazine pharmacology, ECG in transgenic mice\",\n      \"journal\": \"Cardiovascular research\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1-2 — multiple orthogonal systems (hiPSC-CMs, mouse model, cell lines) with molecular and electrophysiological validation\",\n      \"pmids\": [\"33576403\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2002,\n      \"finding\": \"Nav1.5 protein is expressed in the mouse brain, co-localizing with neurofilaments and clustering at high density in neuronal axons, suggesting a role in CNS electrical signal propagation.\",\n      \"method\": \"Immunohistochemistry with Nav1.5-specific antibody in mouse brain sections, co-localization with neurofilament markers\",\n      \"journal\": \"Neuroreport\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 3 — single immunolocalization study without functional validation of the CNS role\",\n      \"pmids\": [\"12499865\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2006,\n      \"finding\": \"Canine intracardiac neurons functionally express Nav1.5 (TTX-resistant sodium current with IC50 ~1.17 µM for TTX, inactivation kinetics consistent with Nav1.5); SCN5A expression confirmed by PCR and sequencing, suggesting intrinsic cardiac ganglia as a site of SCN5A function relevant to autonomically modulated arrhythmias.\",\n      \"method\": \"Patch clamp of dissociated intracardiac neurons, immunohistochemistry, RT-PCR with sequencing\",\n      \"journal\": \"Heart rhythm\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — electrophysiology combined with molecular identification, but functional consequence in arrhythmia context not directly demonstrated\",\n      \"pmids\": [\"16818219\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2015,\n      \"finding\": \"Nav1.5 (SCN5A) promotes breast cancer tumor growth and metastatic dissemination in vivo; stable Nav1.5 knockdown reduces tumor growth, local invasion, and liver/lung/spleen metastasis in an orthotopic model, increases apoptosis, and reduces CD44 expression, suggesting Nav1.5 activity regulates invasion via the CD44-src-cortactin axis.\",\n      \"method\": \"Stable shRNA knockdown of Nav1.5, orthotopic breast cancer xenograft model, TTX-blocked patch clamp in tumor slices confirming functional VGSC activity in vivo\",\n      \"journal\": \"Oncotarget\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — in vivo KD with defined metastatic phenotype plus functional current confirmation in tumor tissue, but pathway placement is partial\",\n      \"pmids\": [\"26452220\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2014,\n      \"finding\": \"Human macrophage SCN5A initiates an innate immune signaling pathway: pharmacological channel stimulation or cytoplasmic poly(I:C) (dsRNA mimic) activates the channel, leading to ADCY8 (adenylate cyclase 8) and ATF2-mediated transcription of SP100-related genes and interferon β. Intracellular poly(I:C) augments inward voltage-sensitive sodium current and inhibits outward nonselective current.\",\n      \"method\": \"Pharmacological channel activation, electrophysiology (whole-cell and intracellular poly(I:C) application), gene expression analysis in human macrophages\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — direct electrophysiological and signaling measurements in native macrophages, but mechanistic pathway validation is partial\",\n      \"pmids\": [\"25368329\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2024,\n      \"finding\": \"Anti-Nav1.5 autoantibodies are present in 90% of Brugada syndrome patients (vs. 6% controls); these autoantibodies significantly reduce sodium current density in cellular models, and injection of BrS patient plasma induces Brugada-like ECG abnormalities in wild-type mice, establishing an immunopathogenic mechanism for BrS independent of SCN5A mutation.\",\n      \"method\": \"Western blot, immunoprecipitation, immunofluorescence screening; patch clamp in HEK293A cells; in vivo plasma injection in wild-type mice with ECG monitoring\",\n      \"journal\": \"European heart journal\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1-2 — direct electrophysiological confirmation of reduced INa by autoantibodies plus in vivo mouse plasma injection phenocopy experiment\",\n      \"pmids\": [\"39078224\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2011,\n      \"finding\": \"The SCN5A-S1103Y African American common polymorphism interacts with the SCN5A-R680H mutation to significantly increase late INa (3.4-fold when co-expressed, 3.6-fold on the same construct) in the major Q1077del splice variant background; intracellular acidosis (pH 6.7) further amplifies this interaction, providing a mechanistic basis for arrhythmic sudden death.\",\n      \"method\": \"Whole-cell patch clamp in HEK293 cells with site-directed mutagenesis; splice-variant-specific expression constructs; intracellular pH manipulation\",\n      \"journal\": \"Physiological genomics\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — rigorous electrophysiology demonstrating splice-variant and polymorphism context-dependent late INa amplification\",\n      \"pmids\": [\"21385947\"],\n      \"is_preprint\": false\n    }\n  ],\n  \"current_model\": \"SCN5A encodes Nav1.5, the principal cardiac voltage-gated sodium channel α-subunit responsible for the rapid depolarization upstroke of the action potential; its expression is transcriptionally regulated by TBX5, GATA4/5, BMAL1/molecular clock, Foxo1, and Wnt/β-catenin signaling, and post-transcriptionally by miR-24 and the mRNA-stabilizing protein HuR, while its membrane trafficking and function are controlled by a multiprotein complex involving dystrophin/syntrophins, CASK (at lateral membranes), and FAT10 (preventing Nedd4-2-mediated ubiquitination/degradation); gain-of-function mutations produce increased late INa causing LQT3 and atrial fibrillation via CaMKII-Nav1.5 positive feedback, while loss-of-function mutations—many acting via dominant-negative mechanisms or ER/Golgi trafficking defects—cause Brugada syndrome, conduction disease, and sick sinus syndrome, with channel mechanosensitivity, an intronic SCN10A enhancer, and anti-Nav1.5 autoantibodies representing additional regulatory and pathogenic mechanisms.\"\n}\n```","stage2_raw":"```json\n{\n  \"mechanistic_narrative\": \"SCN5A encodes Nav1.5, the principal voltage-gated sodium channel α-subunit of the heart, responsible for the rapid depolarization upstroke of the cardiac action potential and essential for normal impulse conduction. Cardiac SCN5A expression is transcriptionally controlled by TBX5, GATA4/GATA5, BMAL1 (circadian clock), Foxo1, and Wnt/β-catenin signaling acting on its promoter and a critical intronic enhancer within the SCN10A locus, while post-transcriptionally it is suppressed by miR-24 and stabilized by the RNA-binding protein HuR [PMID:22728936, PMID:27894866, PMID:23364267, PMID:22400069, PMID:27068063, PMID:24642470, PMID:29457789, PMID:29454929]. Nav1.5 membrane density is regulated by a dystrophin–syntrophin complex at the C-terminus, lateral-membrane CASK-dependent trafficking, and FAT10-mediated protection from Nedd4-2 ubiquitination, while gain-of-function mutations that increase persistent late sodium current (INa) cause long QT syndrome type 3 and atrial fibrillation—amplified by a CaMKII–Nav1.5 positive-feedback loop—and loss-of-function mutations, most of which act through dominant-negative suppression of co-expressed wild-type channels or ER/Golgi trafficking defects, cause Brugada syndrome, cardiac conduction disease, and sudden infant death syndrome [PMID:16857961, PMID:27364017, PMID:33414395, PMID:14736542, PMID:35305865, PMID:11786529, PMID:21677263, PMID:11710892, PMID:18929244]. An autoimmune mechanism involving anti-Nav1.5 autoantibodies that reduce sodium current density and reproduce Brugada-type ECG changes in vivo represents an additional, mutation-independent pathogenic pathway [PMID:39078224].\",\n  \"teleology\": [\n    {\n      \"year\": 2001,\n      \"claim\": \"Establishing that SCN5A gain-of-function mutations increase persistent late INa provided the first mechanistic link between Nav1.5 dysfunction and lethal arrhythmia (SIDS), showing that even modest increases in late current are pathogenic.\",\n      \"evidence\": \"Patch clamp of A997S and R1826H mutant channels in HEK cells showing 2–3-fold increased late INa\",\n      \"pmids\": [\"11710892\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Cellular context limited to heterologous expression; no cardiomyocyte or in vivo validation at that time\"]\n    },\n    {\n      \"year\": 2002,\n      \"claim\": \"Demonstrating that BrS-associated mutations cause ER retention of Nav1.5 established protein trafficking failure as a distinct loss-of-function mechanism, separate from gating defects.\",\n      \"evidence\": \"Confocal imaging showing calnexin co-localization of R1232W/T1620M Nav1.5 and abolished INa in tsA201 cells\",\n      \"pmids\": [\"11786529\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Whether trafficking-defective mutants also exert dominant-negative effects on wild-type channels was not tested\"]\n    },\n    {\n      \"year\": 2003,\n      \"claim\": \"Discovery that the common H558R polymorphism rescues nearby loss-of-function mutations (T512I, M1766L) through intragenic complementation revealed that SCN5A genotype-phenotype relationships depend on cis-allelic context and modifier polymorphisms.\",\n      \"evidence\": \"Patch clamp and immunocytochemistry of single and double mutant constructs in HEK cells\",\n      \"pmids\": [\"12569159\", \"12454206\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Whether intragenic rescue occurs in native cardiomyocytes with endogenous accessory subunits was not tested\", \"Structural basis for complementation unknown\"]\n    },\n    {\n      \"year\": 2003,\n      \"claim\": \"Electrophysiological characterization of mutations in domain I–II linker (L619F) and domain IVS6 (I1768V) mapped distinct structural contributions to Nav1.5 inactivation gating—the linker controlling steady-state inactivation and IVS6 stabilizing the inactivated state.\",\n      \"evidence\": \"Patch clamp with site-directed mutagenesis in HEK cells and Xenopus oocytes\",\n      \"pmids\": [\"12673799\", \"12650885\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"No structural data to explain how these residues interact with the inactivation gate at atomic resolution\"]\n    },\n    {\n      \"year\": 2004,\n      \"claim\": \"A transgenic mouse expressing LQT3 mutation N1325S recapitulated human QT prolongation, spontaneous ventricular arrhythmias, and early afterdepolarizations in vivo, validating the late-INa gain-of-function mechanism and demonstrating mexiletine as a targeted therapy.\",\n      \"evidence\": \"In vivo ECG telemetry, patch clamp on isolated ventricular myocytes, mexiletine pharmacological rescue in transgenic mice\",\n      \"pmids\": [\"14736542\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Single mutation model; generalizability to other LQT3 mutations not established\"]\n    },\n    {\n      \"year\": 2005,\n      \"claim\": \"Demonstration that the BrS mutation L325R exerts a dominant-negative effect on co-expressed wild-type Nav1.5, with fever exacerbation, introduced dominant-negative suppression as a key pathomechanism beyond simple haploinsufficiency.\",\n      \"evidence\": \"Co-expression patch clamp at varying temperatures, pharmacological rescue with mexiletine/curcumin in HEK293 cells\",\n      \"pmids\": [\"15890323\", \"16301357\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Generality of dominant-negative mechanism across BrS variants not yet established at that time\"]\n    },\n    {\n      \"year\": 2006,\n      \"claim\": \"Identification of the dystrophin–syntrophin complex as a required scaffold for Nav1.5 membrane expression established that cardiac sodium current depends on cytoskeletal anchoring at the channel C-terminus.\",\n      \"evidence\": \"Pull-down/mass spectrometry, patch clamp, and ECG in dystrophin-deficient mdx5cv mice showing 50% reduction in Nav1.5 and 29% reduction in INa\",\n      \"pmids\": [\"16857961\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Whether dystrophin loss preferentially affects lateral versus intercalated disc Nav1.5 pools was not resolved\"]\n    },\n    {\n      \"year\": 2008,\n      \"claim\": \"The M1875T mutation linked to familial atrial fibrillation revealed a gain-of-function mechanism (+16.4 mV inactivation shift increasing channel availability) distinct from LQT3 persistent current, showing that different biophysical defects in the same channel produce chamber-specific arrhythmias.\",\n      \"evidence\": \"Patch clamp in HEK cells expressing M1875T Nav1.5\",\n      \"pmids\": [\"18929244\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Why the atrium is preferentially affected over the ventricle was not mechanistically explained\"]\n    },\n    {\n      \"year\": 2010,\n      \"claim\": \"Nav1.5 was shown to be intrinsically mechanosensitive, with membrane stretch shifting activation and inactivation voltage dependence and increasing peak current, providing a biophysical basis for stretch-induced arrhythmias.\",\n      \"evidence\": \"Whole-cell and cell-attached patch clamp with graded pressure application in HEK293 cells\",\n      \"pmids\": [\"21041530\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Whether mechanosensitivity is modulated by accessory subunits or cytoskeletal anchoring in cardiomyocytes was not tested\"]\n    },\n    {\n      \"year\": 2011,\n      \"claim\": \"Discovery of a CaMKII–Nav1.5 positive-feedback loop (late INa activates CaMKII, which phosphorylates Nav1.5 to further increase late INa) provided a molecular amplification mechanism for arrhythmogenesis in LQT3.\",\n      \"evidence\": \"Co-immunoprecipitation, isoform-specific siRNA, CaMKII phosphorylation assays in neonatal rat ventricular myocytes and N1325S transgenic mice\",\n      \"pmids\": [\"21677263\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Specific CaMKII phosphorylation sites on Nav1.5 responsible for current augmentation not mapped in this study\", \"Whether the feedback loop operates similarly in human cardiomyocytes was not shown\"]\n    },\n    {\n      \"year\": 2012,\n      \"claim\": \"Conditional knockout of Tbx5 from the murine ventricular conduction system identified TBX5 as a direct transcriptional activator of Scn5a via a VCS-specific enhancer, establishing the first transcription factor–Nav1.5 regulatory axis essential for fast conduction and survival.\",\n      \"evidence\": \"Cre-mediated VCS-specific Tbx5 KO in mice, in vivo enhancer-reporter assay with T-box site mutagenesis\",\n      \"pmids\": [\"22728936\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Whether TBX5 is sufficient to restore Nav1.5 in diseased conduction tissue was not tested\"]\n    },\n    {\n      \"year\": 2012,\n      \"claim\": \"Foxo1 was identified as a direct transcriptional repressor of SCN5A via insulin-responsive elements in its promoter, linking metabolic and oxidative stress signaling to sodium current regulation.\",\n      \"evidence\": \"ChIP showing Foxo1 occupancy at SCN5A promoter, luciferase reporter, constitutively nuclear Foxo1 and RNAi in HL-1 cardiomyocytes\",\n      \"pmids\": [\"22400069\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"In vivo cardiac-specific Foxo1 manipulation not performed\"]\n    },\n    {\n      \"year\": 2013,\n      \"claim\": \"Demonstration that BMAL1 controls circadian Scn5a expression in cardiomyocytes, with its deletion reducing Nav1.5 and increasing arrhythmia susceptibility, established a molecular clock–cardiac conduction axis.\",\n      \"evidence\": \"Inducible cardiomyocyte-specific Bmal1 KO mice with ECG telemetry, patch clamp, and promoter transactivation assay\",\n      \"pmids\": [\"23364267\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Whether other clock components independently regulate SCN5A or act solely through BMAL1 was not dissected\"]\n    },\n    {\n      \"year\": 2014,\n      \"claim\": \"Identification and deletion of a cardiac enhancer within SCN10A that physically contacts the SCN5A promoter (via 4C-seq) and is required for cardiac Scn5a expression resolved how non-coding GWAS variants at SCN10A influence cardiac conduction through long-range regulation of SCN5A.\",\n      \"evidence\": \"4C-seq chromatin conformation, BAC transgenic enhancer deletion, qPCR in human and mouse heart\",\n      \"pmids\": [\"24642470\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"The transcription factors mediating enhancer–promoter communication at this locus were not fully identified\"]\n    },\n    {\n      \"year\": 2016,\n      \"claim\": \"Multiple transcriptional regulators converging on the SCN5A promoter were characterized: GATA4/GATA5 synergistically activate SCN5A via direct co-occupancy in human ventricle; Wnt/β-catenin–TCF4 represses SCN5A under oxidative stress; and CASK negatively regulates Nav1.5 lateral-membrane trafficking.\",\n      \"evidence\": \"ChIP/Re-ChIP in human heart for GATA4/5; ChIP for β-catenin/TCF4 with siRNA in HL-1 cells; pull-down, TIRF, biotinylation, and in vivo siRNA for CASK in cardiomyocytes\",\n      \"pmids\": [\"27894866\", \"27068063\", \"27364017\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"How CASK versus dystrophin–syntrophin complexes coordinately partition Nav1.5 between lateral membrane and intercalated disc is incompletely understood\"]\n    },\n    {\n      \"year\": 2018,\n      \"claim\": \"Post-transcriptional regulation of SCN5A was defined: miR-24 suppresses SCN5A via a coding-region target modulated by a synonymous SNP, and HuR stabilizes SCN5A mRNA with therapeutic potential demonstrated by AAV9-HuR overexpression improving conduction and reducing arrhythmias post-MI.\",\n      \"evidence\": \"miRNA reporter assays and human expression quantitative analysis for miR-24; RIP and AAV9-HuR overexpression with optical mapping post-MI in mice for HuR\",\n      \"pmids\": [\"29457789\", \"29454929\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Whether miR-24 and HuR act on the same mRNA pool or in distinct subcellular compartments is unknown\"]\n    },\n    {\n      \"year\": 2018,\n      \"claim\": \"BrS-associated Nav1.5 trafficking mutants were shown to additionally impair Kir2.1/2.2 channel function, revealing that Nav1.5 positively modulates IK1 and that trafficking defects reduce both INa and IK1, compounding loss of excitability.\",\n      \"evidence\": \"Co-expression in cell lines, rat cardiomyocytes, hiPSC-CMs, and SCN5A haploinsufficient mice; patch clamp\",\n      \"pmids\": [\"30232268\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"The molecular interface between Nav1.5 and Kir2.x that mediates positive modulation is not structurally defined\"]\n    },\n    {\n      \"year\": 2019,\n      \"claim\": \"K219T-LMNA was shown to epigenetically silence SCN5A by recruiting PRC2 (SUZ12) and depositing H3K27me3 at its promoter, establishing a laminopathy-driven mechanism for sodium channel downregulation correctable by CRISPR/Cas9.\",\n      \"evidence\": \"ChIP for Lamin A/C and H3K27me3 at SCN5A promoter, patch clamp, and CRISPR correction in K219T-LMNA iPSC-CMs\",\n      \"pmids\": [\"31118417\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Whether other LMNA mutations use the same PRC2-dependent mechanism to suppress SCN5A is not established\"]\n    },\n    {\n      \"year\": 2019,\n      \"claim\": \"Genome editing of a conserved enhancer cluster downstream of SCN5A confirmed that multiple enhancer elements within the SCN5A–SCN10A locus cooperatively control chromatin architecture over >0.5 Mb and are selectively required for cardiac Scn5a expression and normal conduction.\",\n      \"evidence\": \"CRISPR-based enhancer deletions in mice with cardiac expression and ECG analysis\",\n      \"pmids\": [\"31666509\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"How the individual enhancers communicate with each other and with the SCN5A promoter in 3D chromatin space is incompletely resolved\"]\n    },\n    {\n      \"year\": 2021,\n      \"claim\": \"FAT10 was identified as a novel Nav1.5 stabilizer that prevents Nedd4-2-mediated ubiquitination by binding Nav1.5 C-terminal lysines, with cardiac-specific Fat10 KO reducing peak INa and increasing arrhythmia susceptibility post-MI.\",\n      \"evidence\": \"Co-IP, ubiquitination assays, conditional cardiac Fat10 KO mice with patch clamp and post-MI arrhythmia phenotyping\",\n      \"pmids\": [\"33414395\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Whether FAT10 competes with ubiquitin at specific lysines or blocks Nedd4-2 access allosterically is unresolved\"]\n    },\n    {\n      \"year\": 2022,\n      \"claim\": \"Systematic co-expression of 50 SCN5A loss-of-function variants with wild-type showed that dominant-negative effects (not haploinsufficiency) are the predominant mechanism for most BrS-associated missense mutations, with a 2.7-fold higher disease burden for dominant-negative variants, redefining the genetic architecture of Brugada syndrome.\",\n      \"evidence\": \"Automated patch clamp with heterozygous WT + mutant co-expression in HEK293T cells; clinical BrS burden comparison\",\n      \"pmids\": [\"35305865\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Structural mechanism by which mutant subunits poison wild-type channel complexes is not resolved\"]\n    },\n    {\n      \"year\": 2022,\n      \"claim\": \"TBX5 variants were shown to cause either BrS (via failure to activate SCN5A promoter) or LQTS (via failure to repress CaMKIIδ/βIV-spectrin, augmenting late INa), demonstrating that a single upstream transcription factor can produce opposing arrhythmia syndromes through distinct transcriptional targets.\",\n      \"evidence\": \"Luciferase reporter, hiPSC-CMs, HL-1 cells, mouse cardiomyocytes, patch clamp, ranolazine pharmacology\",\n      \"pmids\": [\"33576403\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Complete set of TBX5 direct targets relevant to cardiac electrophysiology not defined\"]\n    },\n    {\n      \"year\": 2024,\n      \"claim\": \"Anti-Nav1.5 autoantibodies were identified in 90% of BrS patients, and injection of patient plasma into wild-type mice reproduced BrS-like ECG changes, establishing a mutation-independent autoimmune pathogenic mechanism.\",\n      \"evidence\": \"Western blot/IP screening of patient sera, patch clamp in HEK293A cells treated with patient IgG, in vivo plasma injection in WT mice with ECG\",\n      \"pmids\": [\"39078224\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Epitope(s) recognized by the autoantibodies on Nav1.5 not mapped\", \"Whether autoantibodies are pathogenic drivers or secondary phenomena in BrS requires longitudinal studies\"]\n    },\n    {\n      \"year\": null,\n      \"claim\": \"Key unresolved questions include: the high-resolution structural basis for dominant-negative poisoning of WT by mutant Nav1.5 subunits; the mechanism by which Nav1.5 positively modulates Kir2.x channels; how intercalated disc versus lateral membrane Nav1.5 pools are differentially regulated; and whether anti-Nav1.5 autoantibodies are primary drivers or secondary markers in Brugada syndrome.\",\n      \"evidence\": \"\",\n      \"pmids\": [],\n      \"confidence\": \"Low\",\n      \"gaps\": [\"No cryo-EM structure of full-length human Nav1.5 in complex with trafficking partners or mutant subunits\", \"Molecular interface for Nav1.5–Kir2.x interaction undefined\", \"Relative contributions of autoimmune versus genetic mechanisms in genotype-negative BrS unknown\"]\n    }\n  ],\n  \"mechanism_profile\": {\n    \"molecular_activity\": [\n      {\"term_id\": \"GO:0005215\", \"supporting_discovery_ids\": [2, 7, 15, 24, 28]},\n      {\"term_id\": \"GO:0140299\", \"supporting_discovery_ids\": [15]}\n    ],\n    \"localization\": [\n      {\"term_id\": \"GO:0005886\", \"supporting_discovery_ids\": [0, 1, 6, 10, 22]},\n      {\"term_id\": \"GO:0005783\", \"supporting_discovery_ids\": [1, 4]}\n    ],\n    \"pathway\": [\n      {\"term_id\": \"R-HSA-112316\", \"supporting_discovery_ids\": [2, 7, 15, 24, 28]},\n      {\"term_id\": \"R-HSA-382551\", \"supporting_discovery_ids\": [2, 7, 15, 24]},\n      {\"term_id\": \"R-HSA-74160\", \"supporting_discovery_ids\": [11, 12, 13, 16, 17, 18]},\n      {\"term_id\": \"R-HSA-162582\", \"supporting_discovery_ids\": [8, 17]},\n      {\"term_id\": \"R-HSA-9609507\", \"supporting_discovery_ids\": [1, 6, 10, 22, 23]},\n      {\"term_id\": \"R-HSA-1643685\", \"supporting_discovery_ids\": [2, 5, 24, 34]}\n    ],\n    \"complexes\": [\n      \"Dystrophin-syntrophin complex\"\n    ],\n    \"partners\": [\n      \"SNTA1\",\n      \"SNTB1\",\n      \"DMD\",\n      \"CASK\",\n      \"UBD\",\n      \"CAMK2D\",\n      \"TCAP\",\n      \"ELAVL1\"\n    ],\n    \"other_free_text\": []\n  }\n}\n```"}