{"gene":"TTN","run_date":"2026-06-10T10:51:56","timeline":{"discoveries":[{"year":2002,"finding":"Heterozygous TTN mutations cause familial dilated cardiomyopathy (DCM). A 2-bp insertion in TTN exon 326 causes a frameshift truncating A-band titin; the truncated ~2 MDa protein expressed in skeletal muscle is further cleaved to a 1.14 MDa subfragment by site-specific proteolysis. A missense mutation (Trp930Arg) disrupts a conserved hydrophobic core of an immunoglobulin fold in the Z-disc–I-band transition zone.","method":"Genetic linkage, mutation identification, western blot with epitope-specific anti-titin antibodies demonstrating truncated protein and site-specific cleavage","journal":"Nature genetics","confidence":"High","confidence_rationale":"Tier 2 / Strong — reciprocal western blot with multiple epitope-specific antibodies in a large pedigree, replicated in two independent DCM families","pmids":["11788824"],"is_preprint":false},{"year":2002,"finding":"Mutations in the last exon of TTN (Mex6) cause tibial muscular dystrophy (TMD). An 11-bp deletion/insertion in Mex6 and a Leu→Pro missense in Mex6 (adjacent to the calpain-3 binding site Mex5) lead to specific loss of carboxy-terminal titin epitopes in patient muscle, implicating M-line titin functional defect in disease pathogenesis.","method":"Genetic cosegregation analysis, immunohistochemistry with exon-specific antibodies showing loss of C-terminal titin epitopes in patient muscle biopsies","journal":"American journal of human genetics","confidence":"High","confidence_rationale":"Tier 2 / Strong — cosegregation in 81 patients across 12 families plus immunohistochemical functional confirmation with epitope-specific antibodies","pmids":["12145747"],"is_preprint":false},{"year":2005,"finding":"The same C-terminal M-line TTN Finnish founder mutation (FINmaj) in heterozygosity causes classic tibial muscular dystrophy (TMD), while homozygosity causes the more severe LGMD2J phenotype, establishing a gene-dosage effect at the TTN M-line locus.","method":"Genotyping of 386 individuals; phenotype–genotype correlation in heterozygous vs. homozygous carriers","journal":"Neurology","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — large cohort genotyping with clear genotype–phenotype correlation, single study","pmids":["15728284"],"is_preprint":false},{"year":2010,"finding":"C. elegans TTN-1 (titin ortholog) localizes to the I-band/outer A-band of obliquely striated sarcomeres; six distinct 300-residue segments interact with actin and/or myosin in vitro. Five classes of repetitive sequence elements (PEVT, CEEEI, AAPLE, DispRep, BLUE) are intrinsically disordered in aqueous solution, analogous to vertebrate titin PEVK segments, supporting an elasticity function.","method":"Western blot (~2 MDa band), immunofluorescence localization, in vitro actin/myosin binding assays, circular dichroism spectroscopy, molecular dynamics simulations","journal":"Journal of molecular biology","confidence":"Medium","confidence_rationale":"Tier 1–2 / Moderate — in vitro binding reconstitution plus structural biophysics, single lab","pmids":["20346955"],"is_preprint":false},{"year":2013,"finding":"Autosomal recessive compound heterozygous truncating TTN mutations cause centronuclear myopathy. Biochemical analyses of patient muscle demonstrated increased titin degradation and expression of truncated titin proteins, establishing that loss of full-length titin protein is a direct molecular consequence of these mutations.","method":"Whole-exome/genome sequencing, immunofluorescence on muscle biopsies, splicing assays, gel electrophoresis of patient muscle proteins","journal":"Neurology","confidence":"High","confidence_rationale":"Tier 2 / Moderate — multiple orthogonal biochemical methods (splicing assay, gel electrophoresis, immunofluorescence) confirming truncated protein in patient tissue","pmids":["23975875"],"is_preprint":false},{"year":2013,"finding":"Recessive TTN truncating mutations (five in the M-line region) cause core myopathies with associated heart disease. In vitro functional studies documented the first reported absence of a functional titin kinase domain in humans, caused by an M-line TTN mutation, leading to a severe antenatal phenotype; this implicates the titin kinase domain in cardiac morphogenesis.","method":"TTN M-line-targeted sequencing, whole-exome sequencing, in vitro functional studies of titin kinase domain activity","journal":"Human molecular genetics","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — in vitro kinase domain functional assay plus genetic evidence, single study","pmids":["24105469"],"is_preprint":false},{"year":2017,"finding":"In DCM human hearts with TTN truncating variants (TTNtv), myofibril passive stiffness is reduced ~38% compared to donor controls, but maximum contractile force and the N2BA/N2B titin isoform ratio are unchanged and titin haploinsufficiency is not detected, suggesting passive stiffness reduction is a shared DCM mechanism independent of truncation versus contractile protein mutation.","method":"Isolation of cardiac myofibrils from human DCM hearts (TTNtv and contractile protein mutation patients vs. donor controls); contractility and passive stiffness measurements in vitro","journal":"Scientific reports","confidence":"Medium","confidence_rationale":"Tier 1 / Weak — direct in vitro myofibril mechanics, human tissue, but small n=3 TTNtv samples, single study","pmids":["29093449"],"is_preprint":false},{"year":2018,"finding":"RBM20 regulates alternative splicing of TTN (a major RBM20 splicing target). Novex variant exons (45, 46, 48) of TTN are alternatively spliced in a species-specific manner; RBM20 knockout in rat hearts does not affect splicing of Novex variants, indicating Novex isoform splicing is RBM20-independent. Novex 2 and 3 expression levels are altered in human DCM/ARVC hearts.","method":"Cross-species RT-PCR and sequencing; Rbm20 knockout rat hearts; RT-PCR validation of Novex isoform expression in human cardiomyopathy","journal":"Genes","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — Rbm20 knockout model with direct RT-PCR, multiple species tested, single lab","pmids":["29438341"],"is_preprint":false},{"year":2019,"finding":"A recurrent TTN intron 213 splice variant (c.39974-11T>G), inherited in trans with a second pathogenic TTN variant, causes arthrogryposis multiplex congenita and myopathy. Muscle RNA studies confirmed mis-splicing (in-frame exon 214 skipping or cryptic 3' splice-site use leading to frameshift). Fetal muscle RNA-seq showed predominant inclusion of exons 213–217 in TTN metatranscript-only isoforms, explaining the developmental phenotype and improvement with age.","method":"Muscle-derived RNA studies confirming mis-splicing; RNA-sequencing of 365 adult and 5 fetal muscle samples for exon inclusion quantification","journal":"Human mutation","confidence":"High","confidence_rationale":"Tier 2 / Strong — direct RNA splicing assay in patient muscle plus large-scale RNA-seq in fetal and adult tissues, 8 families","pmids":["31660661"],"is_preprint":false},{"year":2019,"finding":"Titin haploinsufficiency caused by reduced cardiac Ttn expression (via AAV-mediated shRNA in mice) produces DCM with impaired cardiac performance, enlarged LV, and reduced LV wall thickness. Upregulation of Yin Yang 1 (Yy1) suppresses this DCM by modulating cell-growth-related genes and promoting cardiomyocyte cell cycle re-entry via Ccnd1/Ccnd2 upregulation.","method":"AAV-mediated shRNA Ttn knockdown mouse model; echocardiography; RNAseq gene profiling; EdU incorporation; overexpression rescue experiments","journal":"Scientific reports","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — in vivo mouse loss-of-function plus RNAseq and rescue, single lab","pmids":["31705051"],"is_preprint":false},{"year":2021,"finding":"TTN truncating variants (TTNtv) cause DCM primarily via two mechanisms: (1) haploinsufficiency—direct demonstration of reduced full-length titin protein in TTNtv-DCM patient hearts with no compensatory increase in Cronos isoform; (2) toxic truncated titin proteins—present in 21/22 TTNtv-DCM hearts, forming intracellular aggregates with deregulated ubiquitin-dependent protein quality control rather than integrating into sarcomeres. In hiPSC-CM models, A-band TTNtv truncation peptides impair myofibrillogenesis. CRISPR correction of TTNtv eliminated truncated protein and raised wild-type titin, restoring contractility; proteasome inhibition increasing wild-type titin also improved function.","method":"Western blot of 113 DCM and donor heart tissues; hiPSC-CM models with patient-derived and CRISPR-generated TTNtv; engineered heart muscle contractility assays; CRISPR-Cas9 correction; proteasome inhibition","journal":"Science translational medicine","confidence":"High","confidence_rationale":"Tier 1–2 / Strong — multiple orthogonal methods (patient tissue biochemistry, hiPSC-CM, engineered heart muscle, CRISPR correction) in a large cohort, mechanistic rescue experiments","pmids":["34731013"],"is_preprint":false},{"year":2021,"finding":"A-band TTNtv dose-dependently impairs cardiac microtissue twitch force and reduces full-length TTN levels more severely than I-band TTNtv. A-band TTNtv produces abundant truncated TTN peptides that integrate into nascent myofibril-like structures and impair myofibrillogenesis—a mechanism not shared by I-band TTNtv. CRISPR reading-frame repair of the A-band TTNtv restored full-length TTN protein, reduced truncation peptides, and rescued sarcomere function.","method":"hiPSC-CM models with A-band and I-band TTNtv; TTN protein gel electrophoresis; immunofluorescence; 3D cardiac microtissue contractility assays; CRISPR-Cas9 reading frame repair; next-generation sequencing","journal":"Circulation","confidence":"High","confidence_rationale":"Tier 1–2 / Strong — reconstitution in engineered cardiac tissues, quantitative protein assays, CRISPR correction with functional rescue, multiple mechanisms tested","pmids":["34905694"],"is_preprint":false},{"year":2021,"finding":"Noncanonical splice-altering variants in TTN splice regions (especially at donor +5 and acceptor −3 positions) disrupt splicing as confirmed by in vitro splice assay and explain ~1–2% of DCM cases, providing a 10–20% increase in diagnostic yield. SpliceAI showed high positive predictive value (86–95%) but poor sensitivity (15–50%) for detecting these variants.","method":"In vitro splice assay of rare TTN splice region variants from 203 DCM cases and 3329 controls; bioinformatic analysis with SpliceAI","journal":"Circulation. Genomic and precision medicine","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — direct in vitro splice assay, large case-control cohort, single study","pmids":["34461741"],"is_preprint":false},{"year":2021,"finding":"Missense TTN mutations associated with congenital myopathies are strongly destabilizing to the Ig/FN3 domain fold. Biophysical analyses showed that destabilizing missense variants phenocopy truncating variants and are pathogenic when expressed on a truncating background (compound heterozygosity) or in homozygosity, but not in heterozygosity alone.","method":"Biophysical stability assays of expressed TTN domains bearing missense mutations; clinical correlation in 30 patients with compound heterozygous or homozygous TTN variants","journal":"Acta neuropathologica","confidence":"Medium","confidence_rationale":"Tier 1–2 / Moderate — direct biophysical domain stability measurements plus genetic correlation, single lab","pmids":["33449170"],"is_preprint":false},{"year":2021,"finding":"CRISPR activation targeting the TTN promoter or distal regulatory elements in 3D chromatin proximity rescued TTN protein deficits in TTNtv hiPSC-CMs, normalized sarcomere content and contractile function, and increased myofibril assembly-related transcripts—providing direct evidence that haploinsufficiency (rather than solely toxic truncated peptide) is a relevant pathomechanism of TTNtv DCM.","method":"dCas9-VPR CRISPR activation with guide RNAs targeting TTN promoter/regulatory elements; TTN protein gel electrophoresis; RNA sequencing; cardiac microtissue contractility assays; epigenetic/chromatin assays","journal":"Circulation","confidence":"High","confidence_rationale":"Tier 1–2 / Strong — CRISPR activation with multiple guide RNAs, protein quantification, RNA-seq, and functional contractility rescue, orthogonal to prior CRISPR correction work","pmids":["38235591"],"is_preprint":false},{"year":2021,"finding":"Reduction of cardiac Ttn by shRNA in mice activates cardiomyocyte cell cycle re-entry by upregulating Ccnd1 and Ccnd2, but cardiomyocytes do not advance to S phase (no DNA replication by EdU incorporation). Yy1 overexpression further enhances Ccnd1/Ccnd2 and promotes DNA replication, suppressing DCM caused by Ttn insufficiency.","method":"AAV shRNA Ttn knockdown mouse; EdU incorporation assay; qPCR/RNAseq for Ccnd1/Ccnd2; Yy1 overexpression rescue","journal":"Scientific reports","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — in vivo mouse model, EdU replication assay, RNAseq, rescue experiments; single lab","pmids":["31705051"],"is_preprint":false}],"current_model":"Titin (TTN) is a giant sarcomeric scaffold protein spanning from Z-disc to M-line that provides myofibrillar elasticity via intrinsically disordered PEVK/repeat segments; its M-line region contains a kinase domain required for cardiac morphogenesis; disease-causing truncating variants reduce full-length titin (haploinsufficiency) and produce truncated peptides that integrate into nascent myofibrils, impair myofibrillogenesis, and form intracellular aggregates with dysregulated ubiquitin-dependent quality control—with A-band truncations being more pathogenic than I-band truncations in proportion to their myofibril assembly disruption; post-translational stability of titin Ig/FN3 domains is critical for recessive congenital myopathies; and the titin locus produces multiple alternatively spliced isoforms regulated in part by RBM20, with metatranscript-only exons playing developmental roles."},"narrative":{"mechanistic_narrative":"Titin (TTN) is a giant sarcomeric protein whose intrinsically disordered repeat segments provide myofibrillar elasticity and whose distinct structural domains anchor the contractile apparatus from the Z-disc/I-band transition through the A-band to the M-line, with model-organism work demonstrating direct actin and myosin binding by multiple titin segments and circular-dichroism evidence that its PEVK-like repeats are intrinsically disordered, consistent with an elastic, scaffolding role [PMID:20346955]. Heterozygous truncating TTN variants are a major cause of dilated cardiomyopathy (DCM), acting through two convergent mechanisms: haploinsufficiency, the direct reduction of full-length titin shown in patient hearts and recapitulated by Ttn knockdown in mice, and the production of toxic truncated peptides that form intracellular aggregates with deregulated ubiquitin-dependent quality control [PMID:34731013, PMID:31705051]. The A-band/I-band axis governs pathogenicity: A-band truncations generate peptides that integrate into nascent myofibrils and impair myofibrillogenesis more severely than I-band truncations, and CRISPR reading-frame repair or promoter-targeted CRISPR activation restores full-length titin and rescues sarcomere assembly and contractile force [PMID:34905694, PMID:38235591]. At the M-line, mutations in the terminal exons cause tibial muscular dystrophy and, in a gene-dosage manner, the more severe LGMD2J, and loss of the M-line titin kinase domain produces severe cardiac morphogenesis defects [PMID:12145747, PMID:15728284, PMID:24105469]. Recessive truncating and strongly destabilizing missense variants affecting Ig/FN3 domain folding cause congenital myopathies, where loss of full-length titin and increased titin degradation are the shared molecular consequence [PMID:23975875, PMID:33449170]. The TTN locus is heavily alternatively spliced, regulated in part by RBM20 and including metatranscript-only and Novex exons with developmental expression, such that splice-disrupting variants cause myopathy and arthrogryposis whose severity tracks fetal-specific exon usage [PMID:29438341, PMID:31660661, PMID:34461741].","teleology":[{"year":2002,"claim":"Established that titin defects directly cause inherited muscle disease by linking truncating and missense TTN variants to dilated cardiomyopathy and to M-line-restricted tibial muscular dystrophy.","evidence":"Genetic linkage with epitope-specific anti-titin western blot showing truncated/cleaved protein in DCM, and cosegregation with exon-specific immunohistochemistry showing loss of C-terminal epitopes in TMD muscle","pmids":["11788824","12145747"],"confidence":"High","gaps":["Did not resolve whether DCM arises from loss of full-length protein or toxic truncated fragments","Functional consequence of the missense Ig-fold disruption not biochemically dissected"]},{"year":2005,"claim":"Demonstrated a gene-dosage relationship at the TTN M-line, where the same founder mutation produces mild TMD in heterozygotes and severe LGMD2J in homozygotes.","evidence":"Genotyping of 386 individuals with heterozygous vs. homozygous phenotype-genotype correlation","pmids":["15728284"],"confidence":"Medium","gaps":["Molecular basis of the dosage threshold not defined","Single cohort"]},{"year":2010,"claim":"Provided biophysical and biochemical grounding for titin's elastic and scaffolding function by mapping actin/myosin-binding segments and showing repeat elements are intrinsically disordered.","evidence":"In vitro actin/myosin binding assays, circular dichroism, and molecular dynamics on C. elegans TTN-1 segments","pmids":["20346955"],"confidence":"Medium","gaps":["Performed on an invertebrate ortholog rather than human titin","Single lab"]},{"year":2013,"claim":"Extended the disease spectrum to recessive myopathies and implicated the titin kinase domain, showing that loss of full-length titin and absent kinase function underlie centronuclear and core myopathies with cardiac involvement.","evidence":"Exome/genome sequencing with splicing assays and gel electrophoresis of patient muscle, plus in vitro titin kinase domain functional assays","pmids":["23975875","24105469"],"confidence":"High","gaps":["Mechanism connecting kinase loss to cardiac morphogenesis not defined","Kinase substrate(s) not identified"]},{"year":2017,"claim":"Identified reduced passive myofibril stiffness as a contractile-phenotype feature of DCM hearts that was shared across mutation types and, in this sample, not attributable to detectable haploinsufficiency.","evidence":"In vitro passive stiffness and contractility measurements on isolated cardiac myofibrils from human DCM hearts","pmids":["29093449"],"confidence":"Medium","gaps":["Only n=3 TTNtv samples","Failure to detect haploinsufficiency conflicts with later larger cohorts"]},{"year":2018,"claim":"Defined the regulatory architecture of TTN splicing, distinguishing RBM20-dependent splicing from RBM20-independent Novex isoform regulation and linking Novex expression to human cardiomyopathy.","evidence":"Cross-species RT-PCR, Rbm20 knockout rat hearts, and RT-PCR of Novex isoforms in human DCM/ARVC","pmids":["29438341"],"confidence":"Medium","gaps":["Functional role of individual Novex isoforms in the sarcomere not established","Single lab"]},{"year":2019,"claim":"Connected developmental TTN splicing to disease and modeled haploinsufficiency in vivo, showing fetal-specific metatranscript exon usage explains age-improving phenotypes and that reduced cardiac Ttn alone produces DCM.","evidence":"Patient muscle splicing assays with fetal/adult RNA-seq for arthrogryposis, and AAV-shRNA Ttn knockdown mouse with echocardiography and rescue","pmids":["31660661","31705051"],"confidence":"High","gaps":["Mouse knockdown does not separate haploinsufficiency from possible truncated-peptide effects of human variants","Yy1 rescue mechanism on titin protein not directly shown"]},{"year":2021,"claim":"Resolved the dual pathomechanism of TTNtv DCM, demonstrating both reduced full-length titin and toxic aggregation-prone truncated peptides, and proving causality through CRISPR correction and CRISPR activation that restored titin and contractile function.","evidence":"Western blot of 113 DCM/donor hearts, hiPSC-CM and engineered heart muscle with patient-derived and CRISPR-generated TTNtv, CRISPR-Cas9 reading-frame repair, dCas9-VPR promoter activation, and proteasome inhibition","pmids":["34731013","34905694","38235591"],"confidence":"High","gaps":["Relative contribution of haploinsufficiency vs. toxic peptide may vary by variant position and model","Identity and regulation of the ubiquitin-quality-control machinery acting on truncated titin not defined"]},{"year":2021,"claim":"Defined the A-band/I-band positional axis of TTNtv pathogenicity and the biophysical basis of recessive missense disease, showing A-band peptides disrupt myofibrillogenesis and that domain-destabilizing missense variants phenocopy truncations.","evidence":"hiPSC-CM A-band vs I-band TTNtv with protein gels and 3D microtissue contractility, plus biophysical Ig/FN3 domain stability assays with clinical correlation","pmids":["34905694","33449170"],"confidence":"High","gaps":["Structural detail of how truncated peptides incorporate into nascent myofibrils not resolved","Threshold of destabilization required for pathogenicity not quantified"]},{"year":2021,"claim":"Linked titin insufficiency to a regenerative signaling axis, showing Ttn reduction triggers partial cardiomyocyte cell-cycle re-entry that Yy1 can complete to suppress DCM.","evidence":"AAV-shRNA Ttn knockdown mice with EdU incorporation, Ccnd1/Ccnd2 profiling, and Yy1 overexpression rescue","pmids":["31705051"],"confidence":"Medium","gaps":["Mechanism by which titin level controls cyclin D expression unknown","Translation to human cardiomyocytes not shown"]},{"year":null,"claim":"How truncated titin peptides are recognized and routed by ubiquitin-dependent quality control, and the molecular substrate/signaling role of the titin kinase domain in cardiac morphogenesis, remain unresolved.","evidence":"","pmids":[],"confidence":"Medium","gaps":["No E3 ligase or degradation pathway component for truncated titin identified in the corpus","No identified titin kinase substrate","Mechanism coupling titin level to cardiomyocyte cell-cycle genes undefined"]}],"mechanism_profile":{"molecular_activity":[{"term_id":"GO:0008092","term_label":"cytoskeletal protein binding","supporting_discovery_ids":[3]},{"term_id":"GO:0005198","term_label":"structural molecule activity","supporting_discovery_ids":[3,10,11]},{"term_id":"GO:0016740","term_label":"transferase activity","supporting_discovery_ids":[5]}],"localization":[{"term_id":"GO:0005856","term_label":"cytoskeleton","supporting_discovery_ids":[3,10,11]}],"pathway":[{"term_id":"R-HSA-397014","term_label":"Muscle contraction","supporting_discovery_ids":[3,11]},{"term_id":"R-HSA-1643685","term_label":"Disease","supporting_discovery_ids":[0,4,10]},{"term_id":"R-HSA-8953854","term_label":"Metabolism of RNA","supporting_discovery_ids":[7,8,12]}],"complexes":["sarcomere"],"partners":["RBM20","CAPN3","YY1"],"other_free_text":[]}},"prefetch_data":{"uniprot":{"accession":"Q8WZ42","full_name":"Titin","aliases":["Connectin","Rhabdomyosarcoma antigen MU-RMS-40.14"],"length_aa":34350,"mass_kda":3816.0,"function":"Key component in the assembly and functioning of vertebrate striated muscles. By providing connections at the level of individual microfilaments, it contributes to the fine balance of forces between the two halves of the sarcomere. The size and extensibility of the cross-links are the main determinants of sarcomere extensibility properties of muscle. In non-muscle cells, seems to play a role in chromosome condensation and chromosome segregation during mitosis. Might link the lamina network to chromatin or nuclear actin, or both during interphase","subcellular_location":"Cytoplasm; Nucleus","url":"https://www.uniprot.org/uniprotkb/Q8WZ42/entry"},"depmap":{"release":"DepMap","has_data":true,"is_common_essential":false,"resolved_as":"","url":"https://depmap.org/portal/gene/TTN","classification":"Not Classified","n_dependent_lines":5,"n_total_lines":1208,"dependency_fraction":0.0041390728476821195},"opencell":{"profiled":false,"resolved_as":"","ensg_id":"","cell_line_id":"","localizations":[],"interactors":[],"url":"https://opencell.sf.czbiohub.org/search/TTN","total_profiled":1310},"omim":[{"mim_id":"620605","title":"CYTOCHROME P450, FAMILY 27, SUBFAMILY C, MEMBER 1; CYP27C1","url":"https://www.omim.org/entry/620605"},{"mim_id":"618052","title":"CARDIOMYOPATHY, FAMILIAL HYPERTROPHIC, 27; CMH27","url":"https://www.omim.org/entry/618052"},{"mim_id":"617292","title":"TRANSMEMBRANE PROTEIN 150C; TMEM150C","url":"https://www.omim.org/entry/617292"},{"mim_id":"613765","title":"CARDIOMYOPATHY, FAMILIAL HYPERTROPHIC, 9; CMH9","url":"https://www.omim.org/entry/613765"},{"mim_id":"612193","title":"CARDIOMYOPATHY-ASSOCIATED PROTEIN 5; CMYA5","url":"https://www.omim.org/entry/612193"}],"hpa":{"profiled":true,"resolved_as":"","reliability":"","locations":[],"tissue_specificity":"Tissue enhanced","tissue_distribution":"Detected in many","driving_tissues":[{"tissue":"heart muscle","ntpm":151.7},{"tissue":"skeletal muscle","ntpm":861.9},{"tissue":"tongue","ntpm":345.1}],"url":"https://www.proteinatlas.org/search/TTN"},"hgnc":{"alias_symbol":["CMPD4","FLJ32040","TMD","CMH9","LGMD2J","MYLK5"],"prev_symbol":["CMD1G"]},"alphafold":{"accession":"Q8WZ42","domains":[],"viewer_url":"https://alphafold.ebi.ac.uk/entry/Q8WZ42","model_url":"","pae_url":"","plddt_mean":null},"mouse_models":{"mgi_url":"https://www.informatics.jax.org/marker/summary?nomen=TTN","jax_strain_url":"https://www.jax.org/strain/search?query=TTN"},"sequence":{"accession":"Q8WZ42","fasta_url":"https://rest.uniprot.org/uniprotkb/Q8WZ42.fasta","uniprot_url":"https://www.uniprot.org/uniprotkb/Q8WZ42/entry","alphafold_viewer_url":"https://alphafold.ebi.ac.uk/entry/Q8WZ42"}},"corpus_meta":[{"pmid":"11788824","id":"PMC_11788824","title":"Mutations of TTN, encoding the giant muscle filament titin, cause familial dilated cardiomyopathy.","date":"2002","source":"Nature genetics","url":"https://pubmed.ncbi.nlm.nih.gov/11788824","citation_count":453,"is_preprint":false},{"pmid":"12145747","id":"PMC_12145747","title":"Tibial muscular dystrophy is a titinopathy caused by mutations in TTN, the gene encoding the giant skeletal-muscle protein titin.","date":"2002","source":"American journal of human genetics","url":"https://pubmed.ncbi.nlm.nih.gov/12145747","citation_count":331,"is_preprint":false},{"pmid":"24980681","id":"PMC_24980681","title":"A rising titan: TTN review and mutation update.","date":"2014","source":"Human mutation","url":"https://pubmed.ncbi.nlm.nih.gov/24980681","citation_count":193,"is_preprint":false},{"pmid":"23975875","id":"PMC_23975875","title":"Recessive truncating titin gene, TTN, mutations presenting as centronuclear myopathy.","date":"2013","source":"Neurology","url":"https://pubmed.ncbi.nlm.nih.gov/23975875","citation_count":166,"is_preprint":false},{"pmid":"22074755","id":"PMC_22074755","title":"Potential genetic risk factors for chronic TMD: genetic associations from the OPPERA case control study.","date":"2011","source":"The journal of pain","url":"https://pubmed.ncbi.nlm.nih.gov/22074755","citation_count":149,"is_preprint":false},{"pmid":"24105469","id":"PMC_24105469","title":"Recessive TTN truncating mutations define novel forms of core myopathy with heart disease.","date":"2013","source":"Human molecular genetics","url":"https://pubmed.ncbi.nlm.nih.gov/24105469","citation_count":144,"is_preprint":false},{"pmid":"29101304","id":"PMC_29101304","title":"Functional Role of a Novel Long Noncoding RNA TTN-AS1 in Esophageal Squamous Cell Carcinoma Progression and Metastasis.","date":"2017","source":"Clinical cancer research : an official journal of the American Association for Cancer Research","url":"https://pubmed.ncbi.nlm.nih.gov/29101304","citation_count":122,"is_preprint":false},{"pmid":"31600142","id":"PMC_31600142","title":"LncRNA TTN-AS1 regulates osteosarcoma cell apoptosis and drug resistance via the miR-134-5p/MBTD1 axis.","date":"2019","source":"Aging","url":"https://pubmed.ncbi.nlm.nih.gov/31600142","citation_count":112,"is_preprint":false},{"pmid":"34662387","id":"PMC_34662387","title":"Titin (TTN): from molecule to modifications, mechanics, and medical significance.","date":"2022","source":"Cardiovascular research","url":"https://pubmed.ncbi.nlm.nih.gov/34662387","citation_count":110,"is_preprint":false},{"pmid":"31849696","id":"PMC_31849696","title":"The Giant Protein Titin's Role in Cardiomyopathy: Genetic, Transcriptional, and Post-translational Modifications of TTN and Their Contribution to Cardiac Disease.","date":"2019","source":"Frontiers in physiology","url":"https://pubmed.ncbi.nlm.nih.gov/31849696","citation_count":110,"is_preprint":false},{"pmid":"34731013","id":"PMC_34731013","title":"Truncated titin proteins and titin haploinsufficiency are targets for functional recovery in human cardiomyopathy due to TTN mutations.","date":"2021","source":"Science translational 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Clinical electrophysiology","url":"https://pubmed.ncbi.nlm.nih.gov/39453294","citation_count":9,"is_preprint":false},{"pmid":"38563255","id":"PMC_38563255","title":"Oxide and 2D TMD semiconductors for 3D DRAM cell transistors.","date":"2024","source":"Nanoscale horizons","url":"https://pubmed.ncbi.nlm.nih.gov/38563255","citation_count":9,"is_preprint":false},{"pmid":"31705051","id":"PMC_31705051","title":"Upregulation of Yy1 Suppresses Dilated Cardiomyopathy caused by Ttn insufficiency.","date":"2019","source":"Scientific reports","url":"https://pubmed.ncbi.nlm.nih.gov/31705051","citation_count":9,"is_preprint":false},{"pmid":"33445410","id":"PMC_33445410","title":"Clinical Considerations for a Family with Dilated Cardiomyopathy, Sudden Cardiac Death, and a Novel TTN Frameshift Mutation.","date":"2021","source":"International journal of molecular sciences","url":"https://pubmed.ncbi.nlm.nih.gov/33445410","citation_count":9,"is_preprint":false},{"pmid":"31489791","id":"PMC_31489791","title":"A novel TTN deletion in a family with skeletal myopathy, facial weakness, and dilated cardiomyopathy.","date":"2019","source":"Molecular genetics & genomic medicine","url":"https://pubmed.ncbi.nlm.nih.gov/31489791","citation_count":9,"is_preprint":false},{"pmid":"27760846","id":"PMC_27760846","title":"T/Tn immunotherapy avoiding immune deviation.","date":"2016","source":"International journal of immunopathology and pharmacology","url":"https://pubmed.ncbi.nlm.nih.gov/27760846","citation_count":8,"is_preprint":false},{"pmid":"32440207","id":"PMC_32440207","title":"Long Non-Coding RNA TTN-AS1 Serves as a Competing Endogenous RNA of miR-195 to Facilitate Clear Cell Renal Cell Carcinoma Progression.","date":"2020","source":"Cancer management and research","url":"https://pubmed.ncbi.nlm.nih.gov/32440207","citation_count":8,"is_preprint":false},{"pmid":"33693584","id":"PMC_33693584","title":"Implications of an Improved Model of the TSH Receptor Transmembrane Domain (TSHR-TMD-TRIO).","date":"2021","source":"Endocrinology","url":"https://pubmed.ncbi.nlm.nih.gov/33693584","citation_count":8,"is_preprint":false},{"pmid":"29438341","id":"PMC_29438341","title":"Characterization of TTN Novex Splicing Variants across Species and the Role of RBM20 in Novex-Specific Exon Splicing.","date":"2018","source":"Genes","url":"https://pubmed.ncbi.nlm.nih.gov/29438341","citation_count":8,"is_preprint":false},{"pmid":"33746696","id":"PMC_33746696","title":"Digenic Variants in the TTN and TRAPPC11 Genes Co-segregating With a Limb-Girdle Muscular Dystrophy in a Han Chinese Family.","date":"2021","source":"Frontiers in neuroscience","url":"https://pubmed.ncbi.nlm.nih.gov/33746696","citation_count":8,"is_preprint":false},{"pmid":"34141611","id":"PMC_34141611","title":"Silencing of the Long Non-Coding RNA TTN-AS1 Attenuates the Malignant Progression of Osteosarcoma Cells by Regulating the miR-16-1-3p/TFAP4 Axis.","date":"2021","source":"Frontiers in oncology","url":"https://pubmed.ncbi.nlm.nih.gov/34141611","citation_count":8,"is_preprint":false}],"cost":{"stage1":{"model":"claude-sonnet-4-6","input_tokens":54563,"output_tokens":4402,"usd":0.11486,"stage1_stop_reason":"end_turn"},"stage2":{"model":"claude-opus-4-8","input_tokens":12475,"output_tokens":3794,"usd":0.078613,"stage2_stop_reason":"end_turn"},"total_usd":0.193473,"stage1_batch_id":"msgbatch_017qqVz33Ga63SCDwzb35XPb","stage2_batch_id":"msgbatch_01Scr2Ei9x4HJMiRGxwrmvLK","note":"batch pricing = 50% of standard"},"stage1_raw":"```json\n{\n  \"discoveries\": [\n    {\n      \"year\": 2002,\n      \"finding\": \"Heterozygous TTN mutations cause familial dilated cardiomyopathy (DCM). A 2-bp insertion in TTN exon 326 causes a frameshift truncating A-band titin; the truncated ~2 MDa protein expressed in skeletal muscle is further cleaved to a 1.14 MDa subfragment by site-specific proteolysis. A missense mutation (Trp930Arg) disrupts a conserved hydrophobic core of an immunoglobulin fold in the Z-disc–I-band transition zone.\",\n      \"method\": \"Genetic linkage, mutation identification, western blot with epitope-specific anti-titin antibodies demonstrating truncated protein and site-specific cleavage\",\n      \"journal\": \"Nature genetics\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — reciprocal western blot with multiple epitope-specific antibodies in a large pedigree, replicated in two independent DCM families\",\n      \"pmids\": [\"11788824\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2002,\n      \"finding\": \"Mutations in the last exon of TTN (Mex6) cause tibial muscular dystrophy (TMD). An 11-bp deletion/insertion in Mex6 and a Leu→Pro missense in Mex6 (adjacent to the calpain-3 binding site Mex5) lead to specific loss of carboxy-terminal titin epitopes in patient muscle, implicating M-line titin functional defect in disease pathogenesis.\",\n      \"method\": \"Genetic cosegregation analysis, immunohistochemistry with exon-specific antibodies showing loss of C-terminal titin epitopes in patient muscle biopsies\",\n      \"journal\": \"American journal of human genetics\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — cosegregation in 81 patients across 12 families plus immunohistochemical functional confirmation with epitope-specific antibodies\",\n      \"pmids\": [\"12145747\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2005,\n      \"finding\": \"The same C-terminal M-line TTN Finnish founder mutation (FINmaj) in heterozygosity causes classic tibial muscular dystrophy (TMD), while homozygosity causes the more severe LGMD2J phenotype, establishing a gene-dosage effect at the TTN M-line locus.\",\n      \"method\": \"Genotyping of 386 individuals; phenotype–genotype correlation in heterozygous vs. homozygous carriers\",\n      \"journal\": \"Neurology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — large cohort genotyping with clear genotype–phenotype correlation, single study\",\n      \"pmids\": [\"15728284\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2010,\n      \"finding\": \"C. elegans TTN-1 (titin ortholog) localizes to the I-band/outer A-band of obliquely striated sarcomeres; six distinct 300-residue segments interact with actin and/or myosin in vitro. Five classes of repetitive sequence elements (PEVT, CEEEI, AAPLE, DispRep, BLUE) are intrinsically disordered in aqueous solution, analogous to vertebrate titin PEVK segments, supporting an elasticity function.\",\n      \"method\": \"Western blot (~2 MDa band), immunofluorescence localization, in vitro actin/myosin binding assays, circular dichroism spectroscopy, molecular dynamics simulations\",\n      \"journal\": \"Journal of molecular biology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 1–2 / Moderate — in vitro binding reconstitution plus structural biophysics, single lab\",\n      \"pmids\": [\"20346955\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2013,\n      \"finding\": \"Autosomal recessive compound heterozygous truncating TTN mutations cause centronuclear myopathy. Biochemical analyses of patient muscle demonstrated increased titin degradation and expression of truncated titin proteins, establishing that loss of full-length titin protein is a direct molecular consequence of these mutations.\",\n      \"method\": \"Whole-exome/genome sequencing, immunofluorescence on muscle biopsies, splicing assays, gel electrophoresis of patient muscle proteins\",\n      \"journal\": \"Neurology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — multiple orthogonal biochemical methods (splicing assay, gel electrophoresis, immunofluorescence) confirming truncated protein in patient tissue\",\n      \"pmids\": [\"23975875\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2013,\n      \"finding\": \"Recessive TTN truncating mutations (five in the M-line region) cause core myopathies with associated heart disease. In vitro functional studies documented the first reported absence of a functional titin kinase domain in humans, caused by an M-line TTN mutation, leading to a severe antenatal phenotype; this implicates the titin kinase domain in cardiac morphogenesis.\",\n      \"method\": \"TTN M-line-targeted sequencing, whole-exome sequencing, in vitro functional studies of titin kinase domain activity\",\n      \"journal\": \"Human molecular genetics\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — in vitro kinase domain functional assay plus genetic evidence, single study\",\n      \"pmids\": [\"24105469\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2017,\n      \"finding\": \"In DCM human hearts with TTN truncating variants (TTNtv), myofibril passive stiffness is reduced ~38% compared to donor controls, but maximum contractile force and the N2BA/N2B titin isoform ratio are unchanged and titin haploinsufficiency is not detected, suggesting passive stiffness reduction is a shared DCM mechanism independent of truncation versus contractile protein mutation.\",\n      \"method\": \"Isolation of cardiac myofibrils from human DCM hearts (TTNtv and contractile protein mutation patients vs. donor controls); contractility and passive stiffness measurements in vitro\",\n      \"journal\": \"Scientific reports\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 1 / Weak — direct in vitro myofibril mechanics, human tissue, but small n=3 TTNtv samples, single study\",\n      \"pmids\": [\"29093449\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2018,\n      \"finding\": \"RBM20 regulates alternative splicing of TTN (a major RBM20 splicing target). Novex variant exons (45, 46, 48) of TTN are alternatively spliced in a species-specific manner; RBM20 knockout in rat hearts does not affect splicing of Novex variants, indicating Novex isoform splicing is RBM20-independent. Novex 2 and 3 expression levels are altered in human DCM/ARVC hearts.\",\n      \"method\": \"Cross-species RT-PCR and sequencing; Rbm20 knockout rat hearts; RT-PCR validation of Novex isoform expression in human cardiomyopathy\",\n      \"journal\": \"Genes\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — Rbm20 knockout model with direct RT-PCR, multiple species tested, single lab\",\n      \"pmids\": [\"29438341\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2019,\n      \"finding\": \"A recurrent TTN intron 213 splice variant (c.39974-11T>G), inherited in trans with a second pathogenic TTN variant, causes arthrogryposis multiplex congenita and myopathy. Muscle RNA studies confirmed mis-splicing (in-frame exon 214 skipping or cryptic 3' splice-site use leading to frameshift). Fetal muscle RNA-seq showed predominant inclusion of exons 213–217 in TTN metatranscript-only isoforms, explaining the developmental phenotype and improvement with age.\",\n      \"method\": \"Muscle-derived RNA studies confirming mis-splicing; RNA-sequencing of 365 adult and 5 fetal muscle samples for exon inclusion quantification\",\n      \"journal\": \"Human mutation\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — direct RNA splicing assay in patient muscle plus large-scale RNA-seq in fetal and adult tissues, 8 families\",\n      \"pmids\": [\"31660661\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2019,\n      \"finding\": \"Titin haploinsufficiency caused by reduced cardiac Ttn expression (via AAV-mediated shRNA in mice) produces DCM with impaired cardiac performance, enlarged LV, and reduced LV wall thickness. Upregulation of Yin Yang 1 (Yy1) suppresses this DCM by modulating cell-growth-related genes and promoting cardiomyocyte cell cycle re-entry via Ccnd1/Ccnd2 upregulation.\",\n      \"method\": \"AAV-mediated shRNA Ttn knockdown mouse model; echocardiography; RNAseq gene profiling; EdU incorporation; overexpression rescue experiments\",\n      \"journal\": \"Scientific reports\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — in vivo mouse loss-of-function plus RNAseq and rescue, single lab\",\n      \"pmids\": [\"31705051\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2021,\n      \"finding\": \"TTN truncating variants (TTNtv) cause DCM primarily via two mechanisms: (1) haploinsufficiency—direct demonstration of reduced full-length titin protein in TTNtv-DCM patient hearts with no compensatory increase in Cronos isoform; (2) toxic truncated titin proteins—present in 21/22 TTNtv-DCM hearts, forming intracellular aggregates with deregulated ubiquitin-dependent protein quality control rather than integrating into sarcomeres. In hiPSC-CM models, A-band TTNtv truncation peptides impair myofibrillogenesis. CRISPR correction of TTNtv eliminated truncated protein and raised wild-type titin, restoring contractility; proteasome inhibition increasing wild-type titin also improved function.\",\n      \"method\": \"Western blot of 113 DCM and donor heart tissues; hiPSC-CM models with patient-derived and CRISPR-generated TTNtv; engineered heart muscle contractility assays; CRISPR-Cas9 correction; proteasome inhibition\",\n      \"journal\": \"Science translational medicine\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1–2 / Strong — multiple orthogonal methods (patient tissue biochemistry, hiPSC-CM, engineered heart muscle, CRISPR correction) in a large cohort, mechanistic rescue experiments\",\n      \"pmids\": [\"34731013\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2021,\n      \"finding\": \"A-band TTNtv dose-dependently impairs cardiac microtissue twitch force and reduces full-length TTN levels more severely than I-band TTNtv. A-band TTNtv produces abundant truncated TTN peptides that integrate into nascent myofibril-like structures and impair myofibrillogenesis—a mechanism not shared by I-band TTNtv. CRISPR reading-frame repair of the A-band TTNtv restored full-length TTN protein, reduced truncation peptides, and rescued sarcomere function.\",\n      \"method\": \"hiPSC-CM models with A-band and I-band TTNtv; TTN protein gel electrophoresis; immunofluorescence; 3D cardiac microtissue contractility assays; CRISPR-Cas9 reading frame repair; next-generation sequencing\",\n      \"journal\": \"Circulation\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1–2 / Strong — reconstitution in engineered cardiac tissues, quantitative protein assays, CRISPR correction with functional rescue, multiple mechanisms tested\",\n      \"pmids\": [\"34905694\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2021,\n      \"finding\": \"Noncanonical splice-altering variants in TTN splice regions (especially at donor +5 and acceptor −3 positions) disrupt splicing as confirmed by in vitro splice assay and explain ~1–2% of DCM cases, providing a 10–20% increase in diagnostic yield. SpliceAI showed high positive predictive value (86–95%) but poor sensitivity (15–50%) for detecting these variants.\",\n      \"method\": \"In vitro splice assay of rare TTN splice region variants from 203 DCM cases and 3329 controls; bioinformatic analysis with SpliceAI\",\n      \"journal\": \"Circulation. Genomic and precision medicine\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — direct in vitro splice assay, large case-control cohort, single study\",\n      \"pmids\": [\"34461741\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2021,\n      \"finding\": \"Missense TTN mutations associated with congenital myopathies are strongly destabilizing to the Ig/FN3 domain fold. Biophysical analyses showed that destabilizing missense variants phenocopy truncating variants and are pathogenic when expressed on a truncating background (compound heterozygosity) or in homozygosity, but not in heterozygosity alone.\",\n      \"method\": \"Biophysical stability assays of expressed TTN domains bearing missense mutations; clinical correlation in 30 patients with compound heterozygous or homozygous TTN variants\",\n      \"journal\": \"Acta neuropathologica\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 1–2 / Moderate — direct biophysical domain stability measurements plus genetic correlation, single lab\",\n      \"pmids\": [\"33449170\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2021,\n      \"finding\": \"CRISPR activation targeting the TTN promoter or distal regulatory elements in 3D chromatin proximity rescued TTN protein deficits in TTNtv hiPSC-CMs, normalized sarcomere content and contractile function, and increased myofibril assembly-related transcripts—providing direct evidence that haploinsufficiency (rather than solely toxic truncated peptide) is a relevant pathomechanism of TTNtv DCM.\",\n      \"method\": \"dCas9-VPR CRISPR activation with guide RNAs targeting TTN promoter/regulatory elements; TTN protein gel electrophoresis; RNA sequencing; cardiac microtissue contractility assays; epigenetic/chromatin assays\",\n      \"journal\": \"Circulation\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1–2 / Strong — CRISPR activation with multiple guide RNAs, protein quantification, RNA-seq, and functional contractility rescue, orthogonal to prior CRISPR correction work\",\n      \"pmids\": [\"38235591\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2021,\n      \"finding\": \"Reduction of cardiac Ttn by shRNA in mice activates cardiomyocyte cell cycle re-entry by upregulating Ccnd1 and Ccnd2, but cardiomyocytes do not advance to S phase (no DNA replication by EdU incorporation). Yy1 overexpression further enhances Ccnd1/Ccnd2 and promotes DNA replication, suppressing DCM caused by Ttn insufficiency.\",\n      \"method\": \"AAV shRNA Ttn knockdown mouse; EdU incorporation assay; qPCR/RNAseq for Ccnd1/Ccnd2; Yy1 overexpression rescue\",\n      \"journal\": \"Scientific reports\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — in vivo mouse model, EdU replication assay, RNAseq, rescue experiments; single lab\",\n      \"pmids\": [\"31705051\"],\n      \"is_preprint\": false\n    }\n  ],\n  \"current_model\": \"Titin (TTN) is a giant sarcomeric scaffold protein spanning from Z-disc to M-line that provides myofibrillar elasticity via intrinsically disordered PEVK/repeat segments; its M-line region contains a kinase domain required for cardiac morphogenesis; disease-causing truncating variants reduce full-length titin (haploinsufficiency) and produce truncated peptides that integrate into nascent myofibrils, impair myofibrillogenesis, and form intracellular aggregates with dysregulated ubiquitin-dependent quality control—with A-band truncations being more pathogenic than I-band truncations in proportion to their myofibril assembly disruption; post-translational stability of titin Ig/FN3 domains is critical for recessive congenital myopathies; and the titin locus produces multiple alternatively spliced isoforms regulated in part by RBM20, with metatranscript-only exons playing developmental roles.\"\n}\n```","stage2_raw":"{\n  \"mechanistic_narrative\": \"Titin (TTN) is a giant sarcomeric protein whose intrinsically disordered repeat segments provide myofibrillar elasticity and whose distinct structural domains anchor the contractile apparatus from the Z-disc/I-band transition through the A-band to the M-line, with model-organism work demonstrating direct actin and myosin binding by multiple titin segments and circular-dichroism evidence that its PEVK-like repeats are intrinsically disordered, consistent with an elastic, scaffolding role [#3]. Heterozygous truncating TTN variants are a major cause of dilated cardiomyopathy (DCM), acting through two convergent mechanisms: haploinsufficiency, the direct reduction of full-length titin shown in patient hearts and recapitulated by Ttn knockdown in mice, and the production of toxic truncated peptides that form intracellular aggregates with deregulated ubiquitin-dependent quality control [#10, #9]. The A-band/I-band axis governs pathogenicity: A-band truncations generate peptides that integrate into nascent myofibrils and impair myofibrillogenesis more severely than I-band truncations, and CRISPR reading-frame repair or promoter-targeted CRISPR activation restores full-length titin and rescues sarcomere assembly and contractile force [#11, #14]. At the M-line, mutations in the terminal exons cause tibial muscular dystrophy and, in a gene-dosage manner, the more severe LGMD2J, and loss of the M-line titin kinase domain produces severe cardiac morphogenesis defects [#1, #2, #5]. Recessive truncating and strongly destabilizing missense variants affecting Ig/FN3 domain folding cause congenital myopathies, where loss of full-length titin and increased titin degradation are the shared molecular consequence [#4, #13]. The TTN locus is heavily alternatively spliced, regulated in part by RBM20 and including metatranscript-only and Novex exons with developmental expression, such that splice-disrupting variants cause myopathy and arthrogryposis whose severity tracks fetal-specific exon usage [#7, #8, #12].\",\n  \"teleology\": [\n    {\n      \"year\": 2002,\n      \"claim\": \"Established that titin defects directly cause inherited muscle disease by linking truncating and missense TTN variants to dilated cardiomyopathy and to M-line-restricted tibial muscular dystrophy.\",\n      \"evidence\": \"Genetic linkage with epitope-specific anti-titin western blot showing truncated/cleaved protein in DCM, and cosegregation with exon-specific immunohistochemistry showing loss of C-terminal epitopes in TMD muscle\",\n      \"pmids\": [\"11788824\", \"12145747\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Did not resolve whether DCM arises from loss of full-length protein or toxic truncated fragments\", \"Functional consequence of the missense Ig-fold disruption not biochemically dissected\"]\n    },\n    {\n      \"year\": 2005,\n      \"claim\": \"Demonstrated a gene-dosage relationship at the TTN M-line, where the same founder mutation produces mild TMD in heterozygotes and severe LGMD2J in homozygotes.\",\n      \"evidence\": \"Genotyping of 386 individuals with heterozygous vs. homozygous phenotype-genotype correlation\",\n      \"pmids\": [\"15728284\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Molecular basis of the dosage threshold not defined\", \"Single cohort\"]\n    },\n    {\n      \"year\": 2010,\n      \"claim\": \"Provided biophysical and biochemical grounding for titin's elastic and scaffolding function by mapping actin/myosin-binding segments and showing repeat elements are intrinsically disordered.\",\n      \"evidence\": \"In vitro actin/myosin binding assays, circular dichroism, and molecular dynamics on C. elegans TTN-1 segments\",\n      \"pmids\": [\"20346955\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Performed on an invertebrate ortholog rather than human titin\", \"Single lab\"]\n    },\n    {\n      \"year\": 2013,\n      \"claim\": \"Extended the disease spectrum to recessive myopathies and implicated the titin kinase domain, showing that loss of full-length titin and absent kinase function underlie centronuclear and core myopathies with cardiac involvement.\",\n      \"evidence\": \"Exome/genome sequencing with splicing assays and gel electrophoresis of patient muscle, plus in vitro titin kinase domain functional assays\",\n      \"pmids\": [\"23975875\", \"24105469\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Mechanism connecting kinase loss to cardiac morphogenesis not defined\", \"Kinase substrate(s) not identified\"]\n    },\n    {\n      \"year\": 2017,\n      \"claim\": \"Identified reduced passive myofibril stiffness as a contractile-phenotype feature of DCM hearts that was shared across mutation types and, in this sample, not attributable to detectable haploinsufficiency.\",\n      \"evidence\": \"In vitro passive stiffness and contractility measurements on isolated cardiac myofibrils from human DCM hearts\",\n      \"pmids\": [\"29093449\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Only n=3 TTNtv samples\", \"Failure to detect haploinsufficiency conflicts with later larger cohorts\"]\n    },\n    {\n      \"year\": 2018,\n      \"claim\": \"Defined the regulatory architecture of TTN splicing, distinguishing RBM20-dependent splicing from RBM20-independent Novex isoform regulation and linking Novex expression to human cardiomyopathy.\",\n      \"evidence\": \"Cross-species RT-PCR, Rbm20 knockout rat hearts, and RT-PCR of Novex isoforms in human DCM/ARVC\",\n      \"pmids\": [\"29438341\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Functional role of individual Novex isoforms in the sarcomere not established\", \"Single lab\"]\n    },\n    {\n      \"year\": 2019,\n      \"claim\": \"Connected developmental TTN splicing to disease and modeled haploinsufficiency in vivo, showing fetal-specific metatranscript exon usage explains age-improving phenotypes and that reduced cardiac Ttn alone produces DCM.\",\n      \"evidence\": \"Patient muscle splicing assays with fetal/adult RNA-seq for arthrogryposis, and AAV-shRNA Ttn knockdown mouse with echocardiography and rescue\",\n      \"pmids\": [\"31660661\", \"31705051\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Mouse knockdown does not separate haploinsufficiency from possible truncated-peptide effects of human variants\", \"Yy1 rescue mechanism on titin protein not directly shown\"]\n    },\n    {\n      \"year\": 2021,\n      \"claim\": \"Resolved the dual pathomechanism of TTNtv DCM, demonstrating both reduced full-length titin and toxic aggregation-prone truncated peptides, and proving causality through CRISPR correction and CRISPR activation that restored titin and contractile function.\",\n      \"evidence\": \"Western blot of 113 DCM/donor hearts, hiPSC-CM and engineered heart muscle with patient-derived and CRISPR-generated TTNtv, CRISPR-Cas9 reading-frame repair, dCas9-VPR promoter activation, and proteasome inhibition\",\n      \"pmids\": [\"34731013\", \"34905694\", \"38235591\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Relative contribution of haploinsufficiency vs. toxic peptide may vary by variant position and model\", \"Identity and regulation of the ubiquitin-quality-control machinery acting on truncated titin not defined\"]\n    },\n    {\n      \"year\": 2021,\n      \"claim\": \"Defined the A-band/I-band positional axis of TTNtv pathogenicity and the biophysical basis of recessive missense disease, showing A-band peptides disrupt myofibrillogenesis and that domain-destabilizing missense variants phenocopy truncations.\",\n      \"evidence\": \"hiPSC-CM A-band vs I-band TTNtv with protein gels and 3D microtissue contractility, plus biophysical Ig/FN3 domain stability assays with clinical correlation\",\n      \"pmids\": [\"34905694\", \"33449170\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Structural detail of how truncated peptides incorporate into nascent myofibrils not resolved\", \"Threshold of destabilization required for pathogenicity not quantified\"]\n    },\n    {\n      \"year\": 2021,\n      \"claim\": \"Linked titin insufficiency to a regenerative signaling axis, showing Ttn reduction triggers partial cardiomyocyte cell-cycle re-entry that Yy1 can complete to suppress DCM.\",\n      \"evidence\": \"AAV-shRNA Ttn knockdown mice with EdU incorporation, Ccnd1/Ccnd2 profiling, and Yy1 overexpression rescue\",\n      \"pmids\": [\"31705051\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Mechanism by which titin level controls cyclin D expression unknown\", \"Translation to human cardiomyocytes not shown\"]\n    },\n    {\n      \"year\": null,\n      \"claim\": \"How truncated titin peptides are recognized and routed by ubiquitin-dependent quality control, and the molecular substrate/signaling role of the titin kinase domain in cardiac morphogenesis, remain unresolved.\",\n      \"evidence\": \"\",\n      \"pmids\": [],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"No E3 ligase or degradation pathway component for truncated titin identified in the corpus\", \"No identified titin kinase substrate\", \"Mechanism coupling titin level to cardiomyocyte cell-cycle genes undefined\"]\n    }\n  ],\n  \"mechanism_profile\": {\n    \"molecular_activity\": [\n      {\"term_id\": \"GO:0008092\", \"supporting_discovery_ids\": [3]},\n      {\"term_id\": \"GO:0005198\", \"supporting_discovery_ids\": [3, 10, 11]},\n      {\"term_id\": \"GO:0016740\", \"supporting_discovery_ids\": [5]}\n    ],\n    \"localization\": [\n      {\"term_id\": \"GO:0005856\", \"supporting_discovery_ids\": [3, 10, 11]}\n    ],\n    \"pathway\": [\n      {\"term_id\": \"R-HSA-397014\", \"supporting_discovery_ids\": [3, 11]},\n      {\"term_id\": \"R-HSA-1643685\", \"supporting_discovery_ids\": [0, 4, 10]},\n      {\"term_id\": \"R-HSA-8953854\", \"supporting_discovery_ids\": [7, 8, 12]}\n    ],\n    \"complexes\": [\"sarcomere\"],\n    \"partners\": [\"RBM20\", \"CAPN3\", \"YY1\"],\n    \"other_free_text\": []\n  }\n}","audit_flag":null,"evaluation":{"pairwise":"win","faith_supported":6,"faith_total":6,"faith_pct":100.0}}