{"gene":"NEB","run_date":"2026-06-10T05:19:52","timeline":{"discoveries":[{"year":2009,"finding":"Nebulin deficiency in NEM2 patient muscle (markedly reduced nebulin protein levels) causes reduced calcium sensitivity of force generation, slower rate constant of force redevelopment, increased tension cost, reduced rate of cross-bridge attachment, and increased rate of cross-bridge detachment, resulting in a reduced fraction of force-generating cross-bridges.","method":"SDS-PAGE/Western blotting of patient muscle biopsies; skinned myofiber mechanics studies","journal":"Journal of structural biology","confidence":"High","confidence_rationale":"Tier 2 / Strong — reciprocal protein quantification combined with multiple orthogonal mechanical assays on patient-derived fibers, providing mechanistic detail at the cross-bridge level","pmids":["19944167"],"is_preprint":false},{"year":2011,"finding":"Severe NEB mutations that greatly reduce nebulin protein levels lead to markedly impaired myofiber force development and increased tension cost; the severity of mechanical impairment correlates with the degree of nebulin protein reduction.","method":"Western blotting for nebulin protein quantification; skinned myofiber mechanics (force development, tension cost) in patient biopsies","journal":"Skeletal muscle","confidence":"High","confidence_rationale":"Tier 2 / Moderate — protein quantification plus functional mechanics in patient-derived fibers, two orthogonal methods in a single study","pmids":["21798101"],"is_preprint":false},{"year":2011,"finding":"Zebrafish neb mutants with decreased Nebulin protein show impaired force generation, altered (shorter) thin filament length, and formation of nemaline bodies, establishing that nebulin is required for normal thin filament length regulation and contractile force in vivo.","method":"Zebrafish genetic model (recessive neb mutation); force measurement; electron/light microscopy of thin filament length and nemaline body formation","journal":"Disease models & mechanisms","confidence":"High","confidence_rationale":"Tier 2 / Moderate — genetic loss-of-function model with multiple orthogonal readouts (protein level, force, filament length, histopathology)","pmids":["22159874"],"is_preprint":false},{"year":2022,"finding":"NEB mutations disrupt the myosin super-relaxed state (SRX), leading to increased ATP consumption in resting NEB-NM muscle fibers; nebulin deficiency also remodels the metabolic proteome in muscle, including abnormal energy proteins and mitochondrial components.","method":"Biophysical assays for myosin SRX on patient skeletal muscle fibers; untargeted proteomics on isolated myofibers from nebulin-deficient mice","journal":"Acta neuropathologica communications","confidence":"High","confidence_rationale":"Tier 2 / Moderate — direct biophysical measurement of SRX in patient fibers plus proteomics in mouse model, two orthogonal methods","pmids":["36528760"],"is_preprint":false},{"year":2024,"finding":"Truncating NEB variants cause nonsense-mediated decay of the mutant NEB transcript; splicing variants activate cryptic splice sites disrupting nebulin's actin-binding sites; nebulin level positively correlates with thin filament length and with maximal and submaximal tension; a duplication variant in the triplicate region produces a larger nebulin protein and longer thin filaments. Omecamtiv mecarbil (OM) substantially increases submaximal tension in NEM2 patient type-1 fibers, especially when nebulin is most reduced.","method":"mRNA stability/NMD analysis; transcriptomic splice-site analysis; nebulin protein quantification; thin filament length measurement; skinned fiber mechanics; pharmacological treatment (OM) of patient fibers","journal":"Acta neuropathologica","confidence":"High","confidence_rationale":"Tier 2 / Strong — multiple orthogonal methods (transcript, protein, structural, and functional) across a ten-patient cohort in a peer-reviewed study","pmids":["38634969"],"is_preprint":false},{"year":2023,"finding":"Proteomic analysis of the Neb conditional knockout mouse reveals perturbations in mitochondrial function and energetic metabolism; structural and functional studies show abnormal mitochondrial distribution, decreased mitochondrial respiratory function, increased mitochondrial transmembrane potential, and extremely low ATP content in nebulin-deficient muscle.","method":"Proteome-wide analysis of Neb conditional knockout skeletal muscle; Ingenuity Pathway Core Analysis; structural studies (mitochondrial distribution); functional mitochondrial respiratory assays; ATP content measurement","journal":"The American journal of pathology","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — multiple orthogonal structural and functional assays in a KO model, single lab","pmids":["37422147"],"is_preprint":false},{"year":2020,"finding":"A compound heterozygous mouse model carrying one missense mutation at a conserved actin-binding site (p.Tyr2303His) and one nonsense mutation (p.Tyr935*) recapitulates human NEB-NM, demonstrating that nebulin's actin-binding sites are functionally critical for normal sarcomere structure and muscle force production.","method":"Generation of compound heterozygous Neb knock-in mice; in vitro whole-muscle and single myofiber physiology; histological analysis for nemaline bodies","journal":"Acta neuropathologica communications","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — genetic mouse model with actin-binding site mutation plus multiple functional and histological readouts, single lab","pmids":["32066503"],"is_preprint":false},{"year":2024,"finding":"Five zebrafish neb mutant alleles recapitulate NEB-related nemaline myopathy with reduced survival, defective muscle structure, reduced contraction force, shorter thin filaments, electron-dense structures in myofibers, and Z-disk thickening, confirming nebulin's essential roles in thin filament length regulation and contractile function in vivo.","method":"Zebrafish genetic models (five allelic series neb mutants); force measurement; thin filament length analysis; electron microscopy; survival assays","journal":"Human molecular genetics","confidence":"High","confidence_rationale":"Tier 2 / Strong — multiple alleles across multiple outcome measures providing robust in vivo mechanistic validation","pmids":["38493359"],"is_preprint":false},{"year":2024,"finding":"Nebulin isoforms containing exon 143 vs. exon 144 are mutually exclusive and differentially expressed in adult skeletal muscles and during development; a splice variant causing exon 144 skipping leads to a pattern of muscle involvement matching the distribution of exon 144-containing isoforms, establishing that isoform-specific nebulin expression underlies region-specific muscle vulnerability.","method":"Transcriptomic sequencing of patient muscle; MRI pattern analysis correlated with isoform expression data","journal":"HGG advances","confidence":"Medium","confidence_rationale":"Tier 3 / Moderate — transcriptomic splice analysis plus MRI correlation, mechanistic inference from isoform data, single lab","pmids":["39318092"],"is_preprint":false},{"year":2025,"finding":"A CRISPR activation approach induced NEB expression in fibroblasts from a heterozygous mother; RNA sequencing after NMD inhibition confirmed that a maternally inherited intronic NEB variant (c.24486+9C>T) generates a novel splice donor site, causing a 7 bp exon extension and a frameshift, establishing the spliceogenic mechanism of this pathogenic intronic variant.","method":"CRISPR activation to induce NEB expression in fibroblasts; RNA sequencing; NMD inhibition","journal":"Clinical genetics","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — functional splice validation using CRISPR activation and RNA sequencing, single lab, novel approach","pmids":["41186962"],"is_preprint":false},{"year":2025,"finding":"The unexpectedly severe phenotype of the existing NebΔExon55 mouse model is caused by generation of a pseudoexon (containing two premature stop codons) at the deletion site, promoting nonsense-mediated decay; CRISPR editing to remove the pseudoexon restores stable Neb transcript and produces a more faithful, moderate phenotype model of human NEB exon 55 deletion disease.","method":"RNA sequencing to identify pseudoexon; CRISPR gene editing to remove pseudoexon; physiological, histological, and molecular characterization of resulting mice","journal":"Skeletal muscle","confidence":"High","confidence_rationale":"Tier 1-2 / Strong — direct genetic rescue experiment (CRISPR) with RNA sequencing mechanistic validation, multiple orthogonal readouts","pmids":["40108735"],"is_preprint":false},{"year":1991,"finding":"The nebulin gene (Neb) was mapped to the proximal region of mouse chromosome 2, syntenic with the human locus, establishing it as a muscle-specific gene at a defined chromosomal location.","method":"RFLP analysis in recombinant inbred mouse strains; maximum likelihood gene mapping","journal":"Cytogenetics and cell genetics","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — classical genetic mapping with multiple RI strains, standard approach for the era","pmids":["1683831"],"is_preprint":false}],"current_model":"Nebulin (NEB) is a giant sarcomeric protein of the skeletal muscle thin filament that regulates thin filament length, cross-bridge cycling kinetics (attachment and detachment rates), and myofibril alignment; loss or reduction of nebulin decreases calcium sensitivity of force generation, reduces force-generating cross-bridges, destabilizes the myosin super-relaxed state (increasing resting ATP consumption), and impairs mitochondrial function, while pathogenic NEB variants cause these defects via nonsense-mediated mRNA decay, cryptic splice-site activation disrupting actin-binding sites, or copy-number changes in the triplicate region that alter nebulin size and thin filament length."},"narrative":{"mechanistic_narrative":"Nebulin (NEB) is a giant skeletal-muscle thin-filament protein essential for thin-filament length regulation and contractile force generation in the sarcomere [PMID:22159874, PMID:38493359]. Reduction of nebulin protein decreases calcium sensitivity of force, slows force redevelopment, lowers the fraction and attachment rate of force-generating cross-bridges while raising the detachment rate, and increases tension cost, with the severity of mechanical impairment scaling with the degree of nebulin loss [PMID:19944167, PMID:21798101, PMID:38634969]. Beyond cross-bridge regulation, nebulin deficiency destabilizes the myosin super-relaxed state, raising resting ATP consumption, and remodels the metabolic proteome with impaired mitochondrial distribution, respiration, and ATP content [PMID:36528760, PMID:37422147]. Nebulin's actin-binding sites are functionally critical: a knock-in mouse carrying a missense mutation at a conserved actin-binding residue together with a nonsense allele recapitulates human nemaline myopathy [PMID:32066503]. Pathogenic NEB variants cause disease through several converging mechanisms — nonsense-mediated decay of truncating transcripts, cryptic or novel splice-donor activation that disrupts actin-binding regions or introduces frameshifts and pseudoexons, and copy-number changes in the triplicate region that alter nebulin size and thin-filament length [PMID:38634969, PMID:41186962, PMID:40108735]; isoform-specific exon usage (mutually exclusive exons 143/144) underlies region-specific muscle vulnerability [PMID:39318092]. The myosin activator omecamtiv mecarbil increases submaximal tension in NEM2 patient type-1 fibers, particularly where nebulin is most reduced [PMID:38634969].","teleology":[{"year":1991,"claim":"Before its function was dissected, NEB needed to be placed in the genome; mapping established it as a muscle-specific gene at a defined locus syntenic between mouse and human.","evidence":"RFLP analysis across recombinant inbred mouse strains with maximum-likelihood mapping","pmids":["1683831"],"confidence":"Medium","gaps":["No functional or structural information about the protein","Does not address the gene's role in muscle contraction"]},{"year":2009,"claim":"It was unknown how nebulin loss translated into contractile failure; cross-bridge-level mechanics in patient fibers showed reduced calcium sensitivity, fewer force-generating cross-bridges, slower attachment and faster detachment, and increased tension cost.","evidence":"SDS-PAGE/Western quantification plus skinned-myofiber mechanics on NEM2 patient biopsies","pmids":["19944167"],"confidence":"High","gaps":["Does not establish thin-filament-length mechanism directly","Patient material with mixed genetic backgrounds"]},{"year":2011,"claim":"Whether the contractile deficit scaled with protein loss was unresolved; both patient mechanics and a zebrafish loss-of-function model established a dose-dependent relationship and that nebulin is required for normal thin-filament length in vivo.","evidence":"Western quantification with skinned-fiber mechanics in patients; recessive zebrafish neb mutant with force, filament-length, and histology readouts","pmids":["21798101","22159874"],"confidence":"High","gaps":["Molecular basis of length specification not defined","Link between shortened filaments and force deficit correlational"]},{"year":2020,"claim":"The functional importance of nebulin's actin-binding sites was inferred but not directly tested; a compound heterozygous knock-in mouse with a conserved actin-binding-site missense plus a nonsense allele recapitulated human NEB-NM.","evidence":"Neb knock-in mice with whole-muscle and single-fiber physiology and nemaline-body histology","pmids":["32066503"],"confidence":"Medium","gaps":["Single-lab model","Does not isolate the missense allele's effect from the nonsense allele in vivo"]},{"year":2022,"claim":"How nebulin deficiency raises energy demand was unclear; biophysical SRX measurement showed disruption of the myosin super-relaxed state with elevated resting ATP turnover, linking thin-filament defects to a primary myosin energetic phenotype.","evidence":"SRX biophysical assays on patient fibers plus untargeted proteomics in nebulin-deficient mice","pmids":["36528760"],"confidence":"High","gaps":["Mechanism by which nebulin stabilizes the myosin SRX state not defined","Causal chain from SRX loss to clinical weakness incomplete"]},{"year":2023,"claim":"Whether the energy deficit extended to mitochondria was untested; proteomics and functional assays in a conditional knockout revealed abnormal mitochondrial distribution, reduced respiration, altered membrane potential, and very low ATP content.","evidence":"Proteome-wide analysis, pathway analysis, structural and respiratory assays, ATP measurement in Neb conditional KO muscle","pmids":["37422147"],"confidence":"Medium","gaps":["Single-lab KO model","Does not separate primary mitochondrial defect from secondary consequence of contractile dysfunction"]},{"year":2024,"claim":"The molecular routes from genotype to nebulin loss were incompletely catalogued; a ten-patient study tied truncating variants to NMD, splice variants to cryptic-site activation disrupting actin-binding sites, and triplicate-region duplication to longer nebulin and filaments, and showed omecamtiv mecarbil rescues submaximal tension.","evidence":"NMD/mRNA-stability analysis, splice-site transcriptomics, protein and filament-length quantification, skinned-fiber mechanics, and pharmacological treatment across a patient cohort","pmids":["38634969"],"confidence":"High","gaps":["OM rescue tested in fibers, not whole-organism","Triplicate-region copy-number effects characterized in limited cases"]},{"year":2024,"claim":"It was unknown why distinct muscles are differentially affected; allelic zebrafish models confirmed essential thin-filament and force roles, while isoform analysis showed mutually exclusive exon 143/144 usage maps to region-specific muscle vulnerability.","evidence":"Five-allele zebrafish series with force, filament-length, EM, and survival assays; patient transcriptomics with MRI pattern correlation","pmids":["38493359","39318092"],"confidence":"High","gaps":["Mechanistic basis of isoform-specific muscle dependence not resolved","MRI-isoform link is correlative"]},{"year":2025,"claim":"Specific intronic variants and model artifacts required mechanistic validation; CRISPR-activation/RNA-seq confirmed an intronic variant creates a novel splice donor causing a frameshift, and CRISPR removal of an unintended pseudoexon in the NebΔExon55 mouse restored stable transcript and a faithful disease model.","evidence":"CRISPR-activation induction of NEB in fibroblasts with RNA-seq and NMD inhibition; RNA-seq pseudoexon identification with CRISPR editing and multi-modal mouse characterization","pmids":["41186962","40108735"],"confidence":"Medium","gaps":["Splice-validation in fibroblasts, not muscle","Generalizability of pseudoexon correction to other models untested"]},{"year":null,"claim":"How nebulin molecularly specifies thin-filament length and stabilizes the myosin super-relaxed state at the structural level remains unresolved.","evidence":"","pmids":[],"confidence":"High","gaps":["No structural model of nebulin-actin-myosin interaction in the timeline","Mechanism coupling thin-filament defects to SRX destabilization undefined"]}],"mechanism_profile":{"molecular_activity":[{"term_id":"GO:0008092","term_label":"cytoskeletal protein binding","supporting_discovery_ids":[6,4]},{"term_id":"GO:0005198","term_label":"structural molecule activity","supporting_discovery_ids":[2,7]}],"localization":[{"term_id":"GO:0005856","term_label":"cytoskeleton","supporting_discovery_ids":[2,7]}],"pathway":[{"term_id":"R-HSA-397014","term_label":"Muscle contraction","supporting_discovery_ids":[0,1,2]}],"complexes":["sarcomere thin filament"],"partners":["ACTN","ACTIN"],"other_free_text":[]}},"prefetch_data":{"uniprot":{"accession":"P20929","full_name":"Nebulin","aliases":[],"length_aa":8525,"mass_kda":986.7,"function":"This giant muscle protein may be involved in maintaining the structural integrity of sarcomeres and the membrane system associated with the myofibrils. Binds and stabilize F-actin","subcellular_location":"Cytoplasm, myofibril, sarcomere; Cytoplasm, cytoskeleton","url":"https://www.uniprot.org/uniprotkb/P20929/entry"},"depmap":{"release":"DepMap","has_data":true,"is_common_essential":false,"resolved_as":"","url":"https://depmap.org/portal/gene/NEB","classification":"Not Classified","n_dependent_lines":0,"n_total_lines":1208,"dependency_fraction":0.0},"opencell":{"profiled":false,"resolved_as":"","ensg_id":"","cell_line_id":"","localizations":[],"interactors":[],"url":"https://opencell.sf.czbiohub.org/search/NEB","total_profiled":1310},"omim":[{"mim_id":"619807","title":"MYOSIN-BINDING PROTEIN H-LIKE; MYBPHL","url":"https://www.omim.org/entry/619807"},{"mim_id":"619334","title":"ARTHROGRYPOSIS MULTIPLEX CONGENITA 6; AMC6","url":"https://www.omim.org/entry/619334"},{"mim_id":"617468","title":"ARTHROGRYPOSIS MULTIPLEX CONGENITA 1, NEUROGENIC, WITH MYELIN DEFECT; AMC1","url":"https://www.omim.org/entry/617468"},{"mim_id":"617336","title":"CONGENITAL MYOPATHY 24; CMYO24","url":"https://www.omim.org/entry/617336"},{"mim_id":"615348","title":"NEMALINE MYOPATHY 8; NEM8","url":"https://www.omim.org/entry/615348"}],"hpa":{"profiled":true,"resolved_as":"","reliability":"","locations":[],"tissue_specificity":"Group enriched","tissue_distribution":"Detected in many","driving_tissues":[{"tissue":"skeletal muscle","ntpm":7182.0},{"tissue":"tongue","ntpm":2198.5}],"url":"https://www.proteinatlas.org/search/NEB"},"hgnc":{"alias_symbol":["NEB177D"],"prev_symbol":["NEM2"]},"alphafold":{"accession":"P20929","domains":[],"viewer_url":"https://alphafold.ebi.ac.uk/entry/P20929","model_url":"","pae_url":"","plddt_mean":null},"mouse_models":{"mgi_url":"https://www.informatics.jax.org/marker/summary?nomen=NEB","jax_strain_url":"https://www.jax.org/strain/search?query=NEB"},"sequence":{"accession":"P20929","fasta_url":"https://rest.uniprot.org/uniprotkb/P20929.fasta","uniprot_url":"https://www.uniprot.org/uniprotkb/P20929/entry","alphafold_viewer_url":"https://alphafold.ebi.ac.uk/entry/P20929"}},"corpus_meta":[{"pmid":"17137745","id":"PMC_17137745","title":"Interrelationships between negative energy balance (NEB) and IGF regulation in liver of lactating dairy cows.","date":"2006","source":"Domestic animal 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region: only revealed by the targeted nemaline myopathy CGH array.","date":"2015","source":"European journal of human genetics : EJHG","url":"https://pubmed.ncbi.nlm.nih.gov/26197980","citation_count":29,"is_preprint":false},{"pmid":"36528760","id":"PMC_36528760","title":"NEB mutations disrupt the super-relaxed state of myosin and remodel the muscle metabolic proteome in nemaline myopathy.","date":"2022","source":"Acta neuropathologica communications","url":"https://pubmed.ncbi.nlm.nih.gov/36528760","citation_count":27,"is_preprint":false},{"pmid":"22363617","id":"PMC_22363617","title":"The mechanical behavior of mutant K14-R125P keratin bundles and networks in NEB-1 keratinocytes.","date":"2012","source":"PloS one","url":"https://pubmed.ncbi.nlm.nih.gov/22363617","citation_count":25,"is_preprint":false},{"pmid":"11102838","id":"PMC_11102838","title":"In vitro degradation of the Neb-Trypsin modulating oostatic factor (Neb-TMOF) in gut luminal content and hemolymph of the grey fleshfly, 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reports","url":"https://pubmed.ncbi.nlm.nih.gov/33674626","citation_count":3,"is_preprint":false},{"pmid":"38187705","id":"PMC_38187705","title":"Characterization of NEB mutations in patients reveals novel nemaline myopathy disease mechanisms and omecamtiv mecarbil force effects.","date":"2023","source":"bioRxiv : the preprint server for biology","url":"https://pubmed.ncbi.nlm.nih.gov/38187705","citation_count":2,"is_preprint":false},{"pmid":"37025449","id":"PMC_37025449","title":"Case report: Homozygous variants of NEB and KLHL40 in two Arab patients with nemaline myopathy.","date":"2023","source":"Frontiers in genetics","url":"https://pubmed.ncbi.nlm.nih.gov/37025449","citation_count":2,"is_preprint":false},{"pmid":"32062132","id":"PMC_32062132","title":"An integration-free iPSC line (SDQLCHi017-A) derived from a patient with nemaline myopathy-2 disease carrying compound heterozygote mutations in NEB gene.","date":"2020","source":"Stem cell research","url":"https://pubmed.ncbi.nlm.nih.gov/32062132","citation_count":1,"is_preprint":false},{"pmid":"41554370","id":"PMC_41554370","title":"Neurochemical and behavioral evidence of high abuse liability of 3F-NEB, a novel synthetic cathinone.","date":"2026","source":"European journal of pharmacology","url":"https://pubmed.ncbi.nlm.nih.gov/41554370","citation_count":1,"is_preprint":false},{"pmid":"27346010","id":"PMC_27346010","title":"Derivation of NEM2 affected human embryonic stem cell line Genea079.","date":"2016","source":"Stem cell research","url":"https://pubmed.ncbi.nlm.nih.gov/27346010","citation_count":0,"is_preprint":false},{"pmid":"40108735","id":"PMC_40108735","title":"Generation of a novel mouse model of nemaline myopathy due to recurrent NEB exon 55 deletion.","date":"2025","source":"Skeletal muscle","url":"https://pubmed.ncbi.nlm.nih.gov/40108735","citation_count":0,"is_preprint":false},{"pmid":"27346011","id":"PMC_27346011","title":"Derivation of NEM2 affected 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patient muscle (markedly reduced nebulin protein levels) causes reduced calcium sensitivity of force generation, slower rate constant of force redevelopment, increased tension cost, reduced rate of cross-bridge attachment, and increased rate of cross-bridge detachment, resulting in a reduced fraction of force-generating cross-bridges.\",\n      \"method\": \"SDS-PAGE/Western blotting of patient muscle biopsies; skinned myofiber mechanics studies\",\n      \"journal\": \"Journal of structural biology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — reciprocal protein quantification combined with multiple orthogonal mechanical assays on patient-derived fibers, providing mechanistic detail at the cross-bridge level\",\n      \"pmids\": [\"19944167\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2011,\n      \"finding\": \"Severe NEB mutations that greatly reduce nebulin protein levels lead to markedly impaired myofiber force development and increased tension cost; the severity of mechanical impairment correlates with the degree of nebulin protein reduction.\",\n      \"method\": \"Western blotting for nebulin protein quantification; skinned myofiber mechanics (force development, tension cost) in patient biopsies\",\n      \"journal\": \"Skeletal muscle\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — protein quantification plus functional mechanics in patient-derived fibers, two orthogonal methods in a single study\",\n      \"pmids\": [\"21798101\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2011,\n      \"finding\": \"Zebrafish neb mutants with decreased Nebulin protein show impaired force generation, altered (shorter) thin filament length, and formation of nemaline bodies, establishing that nebulin is required for normal thin filament length regulation and contractile force in vivo.\",\n      \"method\": \"Zebrafish genetic model (recessive neb mutation); force measurement; electron/light microscopy of thin filament length and nemaline body formation\",\n      \"journal\": \"Disease models & mechanisms\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — genetic loss-of-function model with multiple orthogonal readouts (protein level, force, filament length, histopathology)\",\n      \"pmids\": [\"22159874\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2022,\n      \"finding\": \"NEB mutations disrupt the myosin super-relaxed state (SRX), leading to increased ATP consumption in resting NEB-NM muscle fibers; nebulin deficiency also remodels the metabolic proteome in muscle, including abnormal energy proteins and mitochondrial components.\",\n      \"method\": \"Biophysical assays for myosin SRX on patient skeletal muscle fibers; untargeted proteomics on isolated myofibers from nebulin-deficient mice\",\n      \"journal\": \"Acta neuropathologica communications\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — direct biophysical measurement of SRX in patient fibers plus proteomics in mouse model, two orthogonal methods\",\n      \"pmids\": [\"36528760\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2024,\n      \"finding\": \"Truncating NEB variants cause nonsense-mediated decay of the mutant NEB transcript; splicing variants activate cryptic splice sites disrupting nebulin's actin-binding sites; nebulin level positively correlates with thin filament length and with maximal and submaximal tension; a duplication variant in the triplicate region produces a larger nebulin protein and longer thin filaments. Omecamtiv mecarbil (OM) substantially increases submaximal tension in NEM2 patient type-1 fibers, especially when nebulin is most reduced.\",\n      \"method\": \"mRNA stability/NMD analysis; transcriptomic splice-site analysis; nebulin protein quantification; thin filament length measurement; skinned fiber mechanics; pharmacological treatment (OM) of patient fibers\",\n      \"journal\": \"Acta neuropathologica\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — multiple orthogonal methods (transcript, protein, structural, and functional) across a ten-patient cohort in a peer-reviewed study\",\n      \"pmids\": [\"38634969\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2023,\n      \"finding\": \"Proteomic analysis of the Neb conditional knockout mouse reveals perturbations in mitochondrial function and energetic metabolism; structural and functional studies show abnormal mitochondrial distribution, decreased mitochondrial respiratory function, increased mitochondrial transmembrane potential, and extremely low ATP content in nebulin-deficient muscle.\",\n      \"method\": \"Proteome-wide analysis of Neb conditional knockout skeletal muscle; Ingenuity Pathway Core Analysis; structural studies (mitochondrial distribution); functional mitochondrial respiratory assays; ATP content measurement\",\n      \"journal\": \"The American journal of pathology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — multiple orthogonal structural and functional assays in a KO model, single lab\",\n      \"pmids\": [\"37422147\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2020,\n      \"finding\": \"A compound heterozygous mouse model carrying one missense mutation at a conserved actin-binding site (p.Tyr2303His) and one nonsense mutation (p.Tyr935*) recapitulates human NEB-NM, demonstrating that nebulin's actin-binding sites are functionally critical for normal sarcomere structure and muscle force production.\",\n      \"method\": \"Generation of compound heterozygous Neb knock-in mice; in vitro whole-muscle and single myofiber physiology; histological analysis for nemaline bodies\",\n      \"journal\": \"Acta neuropathologica communications\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — genetic mouse model with actin-binding site mutation plus multiple functional and histological readouts, single lab\",\n      \"pmids\": [\"32066503\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2024,\n      \"finding\": \"Five zebrafish neb mutant alleles recapitulate NEB-related nemaline myopathy with reduced survival, defective muscle structure, reduced contraction force, shorter thin filaments, electron-dense structures in myofibers, and Z-disk thickening, confirming nebulin's essential roles in thin filament length regulation and contractile function in vivo.\",\n      \"method\": \"Zebrafish genetic models (five allelic series neb mutants); force measurement; thin filament length analysis; electron microscopy; survival assays\",\n      \"journal\": \"Human molecular genetics\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — multiple alleles across multiple outcome measures providing robust in vivo mechanistic validation\",\n      \"pmids\": [\"38493359\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2024,\n      \"finding\": \"Nebulin isoforms containing exon 143 vs. exon 144 are mutually exclusive and differentially expressed in adult skeletal muscles and during development; a splice variant causing exon 144 skipping leads to a pattern of muscle involvement matching the distribution of exon 144-containing isoforms, establishing that isoform-specific nebulin expression underlies region-specific muscle vulnerability.\",\n      \"method\": \"Transcriptomic sequencing of patient muscle; MRI pattern analysis correlated with isoform expression data\",\n      \"journal\": \"HGG advances\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 3 / Moderate — transcriptomic splice analysis plus MRI correlation, mechanistic inference from isoform data, single lab\",\n      \"pmids\": [\"39318092\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2025,\n      \"finding\": \"A CRISPR activation approach induced NEB expression in fibroblasts from a heterozygous mother; RNA sequencing after NMD inhibition confirmed that a maternally inherited intronic NEB variant (c.24486+9C>T) generates a novel splice donor site, causing a 7 bp exon extension and a frameshift, establishing the spliceogenic mechanism of this pathogenic intronic variant.\",\n      \"method\": \"CRISPR activation to induce NEB expression in fibroblasts; RNA sequencing; NMD inhibition\",\n      \"journal\": \"Clinical genetics\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — functional splice validation using CRISPR activation and RNA sequencing, single lab, novel approach\",\n      \"pmids\": [\"41186962\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2025,\n      \"finding\": \"The unexpectedly severe phenotype of the existing NebΔExon55 mouse model is caused by generation of a pseudoexon (containing two premature stop codons) at the deletion site, promoting nonsense-mediated decay; CRISPR editing to remove the pseudoexon restores stable Neb transcript and produces a more faithful, moderate phenotype model of human NEB exon 55 deletion disease.\",\n      \"method\": \"RNA sequencing to identify pseudoexon; CRISPR gene editing to remove pseudoexon; physiological, histological, and molecular characterization of resulting mice\",\n      \"journal\": \"Skeletal muscle\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1-2 / Strong — direct genetic rescue experiment (CRISPR) with RNA sequencing mechanistic validation, multiple orthogonal readouts\",\n      \"pmids\": [\"40108735\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1991,\n      \"finding\": \"The nebulin gene (Neb) was mapped to the proximal region of mouse chromosome 2, syntenic with the human locus, establishing it as a muscle-specific gene at a defined chromosomal location.\",\n      \"method\": \"RFLP analysis in recombinant inbred mouse strains; maximum likelihood gene mapping\",\n      \"journal\": \"Cytogenetics and cell genetics\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — classical genetic mapping with multiple RI strains, standard approach for the era\",\n      \"pmids\": [\"1683831\"],\n      \"is_preprint\": false\n    }\n  ],\n  \"current_model\": \"Nebulin (NEB) is a giant sarcomeric protein of the skeletal muscle thin filament that regulates thin filament length, cross-bridge cycling kinetics (attachment and detachment rates), and myofibril alignment; loss or reduction of nebulin decreases calcium sensitivity of force generation, reduces force-generating cross-bridges, destabilizes the myosin super-relaxed state (increasing resting ATP consumption), and impairs mitochondrial function, while pathogenic NEB variants cause these defects via nonsense-mediated mRNA decay, cryptic splice-site activation disrupting actin-binding sites, or copy-number changes in the triplicate region that alter nebulin size and thin filament length.\"\n}\n```","stage2_raw":"{\n  \"mechanistic_narrative\": \"Nebulin (NEB) is a giant skeletal-muscle thin-filament protein essential for thin-filament length regulation and contractile force generation in the sarcomere [#2, #7]. Reduction of nebulin protein decreases calcium sensitivity of force, slows force redevelopment, lowers the fraction and attachment rate of force-generating cross-bridges while raising the detachment rate, and increases tension cost, with the severity of mechanical impairment scaling with the degree of nebulin loss [#0, #1, #4]. Beyond cross-bridge regulation, nebulin deficiency destabilizes the myosin super-relaxed state, raising resting ATP consumption, and remodels the metabolic proteome with impaired mitochondrial distribution, respiration, and ATP content [#3, #5]. Nebulin's actin-binding sites are functionally critical: a knock-in mouse carrying a missense mutation at a conserved actin-binding residue together with a nonsense allele recapitulates human nemaline myopathy [#6]. Pathogenic NEB variants cause disease through several converging mechanisms — nonsense-mediated decay of truncating transcripts, cryptic or novel splice-donor activation that disrupts actin-binding regions or introduces frameshifts and pseudoexons, and copy-number changes in the triplicate region that alter nebulin size and thin-filament length [#4, #9, #10]; isoform-specific exon usage (mutually exclusive exons 143/144) underlies region-specific muscle vulnerability [#8]. The myosin activator omecamtiv mecarbil increases submaximal tension in NEM2 patient type-1 fibers, particularly where nebulin is most reduced [#4].\",\n  \"teleology\": [\n    {\n      \"year\": 1991,\n      \"claim\": \"Before its function was dissected, NEB needed to be placed in the genome; mapping established it as a muscle-specific gene at a defined locus syntenic between mouse and human.\",\n      \"evidence\": \"RFLP analysis across recombinant inbred mouse strains with maximum-likelihood mapping\",\n      \"pmids\": [\"1683831\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"No functional or structural information about the protein\", \"Does not address the gene's role in muscle contraction\"]\n    },\n    {\n      \"year\": 2009,\n      \"claim\": \"It was unknown how nebulin loss translated into contractile failure; cross-bridge-level mechanics in patient fibers showed reduced calcium sensitivity, fewer force-generating cross-bridges, slower attachment and faster detachment, and increased tension cost.\",\n      \"evidence\": \"SDS-PAGE/Western quantification plus skinned-myofiber mechanics on NEM2 patient biopsies\",\n      \"pmids\": [\"19944167\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Does not establish thin-filament-length mechanism directly\", \"Patient material with mixed genetic backgrounds\"]\n    },\n    {\n      \"year\": 2011,\n      \"claim\": \"Whether the contractile deficit scaled with protein loss was unresolved; both patient mechanics and a zebrafish loss-of-function model established a dose-dependent relationship and that nebulin is required for normal thin-filament length in vivo.\",\n      \"evidence\": \"Western quantification with skinned-fiber mechanics in patients; recessive zebrafish neb mutant with force, filament-length, and histology readouts\",\n      \"pmids\": [\"21798101\", \"22159874\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Molecular basis of length specification not defined\", \"Link between shortened filaments and force deficit correlational\"]\n    },\n    {\n      \"year\": 2020,\n      \"claim\": \"The functional importance of nebulin's actin-binding sites was inferred but not directly tested; a compound heterozygous knock-in mouse with a conserved actin-binding-site missense plus a nonsense allele recapitulated human NEB-NM.\",\n      \"evidence\": \"Neb knock-in mice with whole-muscle and single-fiber physiology and nemaline-body histology\",\n      \"pmids\": [\"32066503\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Single-lab model\", \"Does not isolate the missense allele's effect from the nonsense allele in vivo\"]\n    },\n    {\n      \"year\": 2022,\n      \"claim\": \"How nebulin deficiency raises energy demand was unclear; biophysical SRX measurement showed disruption of the myosin super-relaxed state with elevated resting ATP turnover, linking thin-filament defects to a primary myosin energetic phenotype.\",\n      \"evidence\": \"SRX biophysical assays on patient fibers plus untargeted proteomics in nebulin-deficient mice\",\n      \"pmids\": [\"36528760\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Mechanism by which nebulin stabilizes the myosin SRX state not defined\", \"Causal chain from SRX loss to clinical weakness incomplete\"]\n    },\n    {\n      \"year\": 2023,\n      \"claim\": \"Whether the energy deficit extended to mitochondria was untested; proteomics and functional assays in a conditional knockout revealed abnormal mitochondrial distribution, reduced respiration, altered membrane potential, and very low ATP content.\",\n      \"evidence\": \"Proteome-wide analysis, pathway analysis, structural and respiratory assays, ATP measurement in Neb conditional KO muscle\",\n      \"pmids\": [\"37422147\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Single-lab KO model\", \"Does not separate primary mitochondrial defect from secondary consequence of contractile dysfunction\"]\n    },\n    {\n      \"year\": 2024,\n      \"claim\": \"The molecular routes from genotype to nebulin loss were incompletely catalogued; a ten-patient study tied truncating variants to NMD, splice variants to cryptic-site activation disrupting actin-binding sites, and triplicate-region duplication to longer nebulin and filaments, and showed omecamtiv mecarbil rescues submaximal tension.\",\n      \"evidence\": \"NMD/mRNA-stability analysis, splice-site transcriptomics, protein and filament-length quantification, skinned-fiber mechanics, and pharmacological treatment across a patient cohort\",\n      \"pmids\": [\"38634969\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"OM rescue tested in fibers, not whole-organism\", \"Triplicate-region copy-number effects characterized in limited cases\"]\n    },\n    {\n      \"year\": 2024,\n      \"claim\": \"It was unknown why distinct muscles are differentially affected; allelic zebrafish models confirmed essential thin-filament and force roles, while isoform analysis showed mutually exclusive exon 143/144 usage maps to region-specific muscle vulnerability.\",\n      \"evidence\": \"Five-allele zebrafish series with force, filament-length, EM, and survival assays; patient transcriptomics with MRI pattern correlation\",\n      \"pmids\": [\"38493359\", \"39318092\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Mechanistic basis of isoform-specific muscle dependence not resolved\", \"MRI-isoform link is correlative\"]\n    },\n    {\n      \"year\": 2025,\n      \"claim\": \"Specific intronic variants and model artifacts required mechanistic validation; CRISPR-activation/RNA-seq confirmed an intronic variant creates a novel splice donor causing a frameshift, and CRISPR removal of an unintended pseudoexon in the NebΔExon55 mouse restored stable transcript and a faithful disease model.\",\n      \"evidence\": \"CRISPR-activation induction of NEB in fibroblasts with RNA-seq and NMD inhibition; RNA-seq pseudoexon identification with CRISPR editing and multi-modal mouse characterization\",\n      \"pmids\": [\"41186962\", \"40108735\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Splice-validation in fibroblasts, not muscle\", \"Generalizability of pseudoexon correction to other models untested\"]\n    },\n    {\n      \"year\": null,\n      \"claim\": \"How nebulin molecularly specifies thin-filament length and stabilizes the myosin super-relaxed state at the structural level remains unresolved.\",\n      \"evidence\": \"\",\n      \"pmids\": [],\n      \"confidence\": \"High\",\n      \"gaps\": [\"No structural model of nebulin-actin-myosin interaction in the timeline\", \"Mechanism coupling thin-filament defects to SRX destabilization undefined\"]\n    }\n  ],\n  \"mechanism_profile\": {\n    \"molecular_activity\": [\n      {\"term_id\": \"GO:0008092\", \"supporting_discovery_ids\": [6, 4]},\n      {\"term_id\": \"GO:0005198\", \"supporting_discovery_ids\": [2, 7]}\n    ],\n    \"localization\": [\n      {\"term_id\": \"GO:0005856\", \"supporting_discovery_ids\": [2, 7]}\n    ],\n    \"pathway\": [\n      {\"term_id\": \"R-HSA-397014\", \"supporting_discovery_ids\": [0, 1, 2]}\n    ],\n    \"complexes\": [\"sarcomere thin filament\"],\n    \"partners\": [\"ACTN\", \"actin\"],\n    \"other_free_text\": []\n  }\n}","audit_flag":null,"evaluation":{"pairwise":"win","faith_supported":6,"faith_total":6,"faith_pct":100.0}}