{"gene":"GYG1","run_date":"2026-06-10T01:55:21","timeline":{"discoveries":[{"year":2017,"finding":"A novel GYG1 missense mutation (c.403G>A; p.Gly135Arg) located in the substrate binding domain abolishes the enzymatic autoglucosylation function of glycogenin-1, as demonstrated by an in vitro autoglucosylation assay. The mutation also caused reduced expression of glycogenin-1 protein.","method":"In vitro autoglucosylation assay; protein expression analysis of patient muscle tissue","journal":"Acta neurologica Scandinavica","confidence":"Medium","confidence_rationale":"Tier 1 / Weak — direct in vitro enzymatic assay with mutant protein, single lab, single study","pmids":["29143313"],"is_preprint":false},{"year":2019,"finding":"Loss-of-function variants in GYG1 (including splice acceptor, frameshift, and missense variants) result in either total absence or reduced expression of glycogenin-1 protein, and residual mutant protein (p.Asp102His) is non-functional, leading to glycogen and polyglucosan storage in skeletal muscle fibers.","method":"Protein expression analysis (Western blot) of patient muscle biopsies; PAS staining and electron microscopy of muscle; functional inference from variant type","journal":"Neuromuscular disorders : NMD","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — protein analysis with multiple patients, two orthogonal morphological methods, single lab","pmids":["31791869"],"is_preprint":false},{"year":2017,"finding":"GYG1 mutations causing loss or reduction of glycogenin-1 expression result in impaired glucosylation activity, as shown by protein analysis of patient muscle biopsies revealing either absence of glycogenin-1 or reduced expression with impaired glucosylation.","method":"Protein analysis of patient muscle biopsies (Western blot/immunohistochemistry); direct sequencing and exome sequencing for variant identification","journal":"Neurology. Genetics","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — multiple families, protein-level functional readout, replicated across multiple patients and labs","pmids":["29264399"],"is_preprint":false},{"year":2026,"finding":"In GSD15 (GYG1 cardiomyopathy), storage material in cardiomyocytes is enriched in proteins involved in glycogen metabolism (glycogen synthase, UDP-glucose pyrophosphorylase 2, glycogenin-1, glycogen phosphorylase, glycogen debranching enzyme), as well as sequestosome 1 (p62) and desmin, without evidence of increased autophagocytosis. Whole-tissue proteomics revealed upregulation of cardiomyopathy biomarkers and downregulation of mitochondrial proteins, indicating impaired energy metabolism.","method":"Laser capture microdissection followed by quantitative mass spectrometry; immunohistochemistry; whole-tissue quantitative mass spectrometry of patient heart explants vs. controls","journal":"The Journal of clinical endocrinology and metabolism","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — multiple orthogonal methods (LCM-MS, IHC, whole-tissue MS) in patient tissue, single lab","pmids":["42165248"],"is_preprint":false},{"year":2025,"finding":"In vivo knockdown of Gyg1 via LNP-mediated siRNA delivery in an LPS-induced sepsis mouse model significantly reduced glycogen content in myeloid cells, attenuated IL-6 and TNF-α production, alleviated LPS-induced neutrophilia, and modestly decreased CD40 expression in monocytes and dendritic cells, improving survival.","method":"LNP-mediated siRNA knockdown in vivo (LPS mouse model); glycogen content measurement; cytokine assays; flow cytometry","journal":"Frontiers in immunology","confidence":"Medium","confidence_rationale":"Tier 2 / Weak — in vivo loss-of-function with defined cellular phenotype, single lab, single study","pmids":["41333476"],"is_preprint":false},{"year":2026,"finding":"RNA sequencing of patient muscle confirmed that the GYG1 splice-site variant c.143+3G>C causes exon 2 skipping, and the deep intronic variant c.7+992T>G activates a cryptic exon insertion, both leading to aberrant GYG1 transcripts. Long-read genome sequencing established that these two variants are in trans (compound heterozygous).","method":"RNA sequencing (RNA-seq); long-read genome sequencing; long-range PCR","journal":"Clinical genetics","confidence":"Medium","confidence_rationale":"Tier 2 / Weak — RNA-seq and long-read GS directly confirm splicing mechanism, single case, single lab","pmids":["42023422"],"is_preprint":false}],"current_model":"GYG1 encodes glycogenin-1, the auto-glucosylating primer enzyme required for glycogen synthesis; loss-of-function or enzymatically null mutations (including missense variants in the substrate-binding domain, frameshift, splice-site, and deep intronic variants causing aberrant splicing) abolish autoglucosylation activity, leading to polyglucosan accumulation in skeletal muscle and cardiomyocytes, sequestration of glycogen-metabolism proteins, disruption of mitochondrial and sarcomeric architecture, and—in myeloid cells—metabolic fueling of inflammatory activation that can be attenuated by Gyg1 knockdown."},"narrative":{"mechanistic_narrative":"GYG1 encodes glycogenin-1, the auto-glucosylating priming enzyme required for glycogen synthesis, whose loss disrupts glycogen homeostasis across multiple tissues [PMID:29143313, PMID:29264399]. Disease-associated variants—including a substrate-binding-domain missense mutation (p.Gly135Arg), additional missense (p.Asp102His), frameshift, splice-acceptor, and deep intronic variants—abolish or reduce glycogenin-1 expression and eliminate autoglucosylation activity, as established directly by in vitro autoglucosylation assays and patient-muscle protein analysis [PMID:29143313, PMID:31791869, PMID:29264399]. Splice-disrupting alleles act through exon 2 skipping and cryptic exon activation, producing aberrant transcripts that can occur in trans as compound heterozygous lesions [PMID:42023422]. Enzymatic failure leads to accumulation of polyglucosan storage material in skeletal muscle fibers and cardiomyocytes [PMID:31791869, PMID:42165248]. In GYG1 cardiomyopathy (GSD15), this storage material sequesters glycogen-metabolism enzymes (glycogen synthase, UDP-glucose pyrophosphorylase 2, glycogenin-1, glycogen phosphorylase, debranching enzyme) along with p62 and desmin, accompanied by downregulation of mitochondrial proteins indicating impaired energy metabolism, without increased autophagy [PMID:42165248]. Beyond its role in storage disease, glycogenin-1-dependent glycogen supports inflammatory activation of myeloid cells: in vivo Gyg1 knockdown lowers myeloid glycogen, attenuates IL-6 and TNF-α production and neutrophilia, and improves survival in LPS-induced sepsis [PMID:41333476].","teleology":[{"year":2017,"claim":"It was unknown whether specific GYG1 missense variants directly impair catalytic function rather than merely correlating with disease; an in vitro assay established that a substrate-binding-domain mutation abolishes autoglucosylation activity.","evidence":"In vitro autoglucosylation assay with mutant protein plus patient muscle protein expression analysis","pmids":["29143313"],"confidence":"Medium","gaps":["Single variant tested in a single study","Effect on downstream glycogen synthesis not directly measured","No structural data on the substrate-binding domain"]},{"year":2017,"claim":"Whether diverse GYG1 mutations converge on a common loss-of-expression/loss-of-glucosylation mechanism was unresolved; protein analysis across multiple families showed absence or reduced glycogenin-1 with impaired glucosylation.","evidence":"Western blot/immunohistochemistry of patient muscle biopsies with exome and direct sequencing","pmids":["29264399"],"confidence":"Medium","gaps":["Functional inference partly from variant type rather than direct enzymatic assay","Genotype-phenotype correlation across tissues not established"]},{"year":2019,"claim":"It was unclear whether residual mutant protein retains function; analysis showed loss-of-function variants yield absent or non-functional glycogenin-1 and drive glycogen/polyglucosan storage in muscle fibers.","evidence":"Western blot, PAS staining, and electron microscopy of patient muscle biopsies","pmids":["31791869"],"confidence":"Medium","gaps":["Functional status inferred from variant type for several alleles","Mechanism linking enzyme loss to polyglucosan structure not resolved"]},{"year":2025,"claim":"Whether glycogenin-1-dependent glycogen has a role beyond storage disease was untested; knockdown showed myeloid glycogen fuels inflammatory cytokine production and that lowering it improves sepsis outcomes.","evidence":"LNP-mediated siRNA Gyg1 knockdown in LPS sepsis mouse model with glycogen, cytokine, and flow cytometry readouts","pmids":["41333476"],"confidence":"Medium","gaps":["Single in vivo study","Cell-intrinsic vs systemic contribution not dissected","Mechanism linking glycogen to cytokine output not defined"]},{"year":2026,"claim":"The composition of cardiac storage material in GYG1 cardiomyopathy was unknown; proteomics revealed enrichment of sequestered glycogen-metabolism enzymes, p62, and desmin alongside mitochondrial protein downregulation.","evidence":"Laser capture microdissection mass spectrometry, whole-tissue MS, and immunohistochemistry of patient heart explants vs controls","pmids":["42165248"],"confidence":"Medium","gaps":["Single lab, limited patient samples","Causal link between protein sequestration and mitochondrial dysfunction not established","No mechanism for absence of autophagic clearance"]},{"year":2026,"claim":"The molecular consequence of non-coding GYG1 variants was uncharacterized; transcript and genome analysis confirmed exon skipping and cryptic exon activation arising from compound heterozygous in-trans alleles.","evidence":"RNA-seq, long-read genome sequencing, and long-range PCR of patient material","pmids":["42023422"],"confidence":"Medium","gaps":["Single case","Quantitative effect on protein output not measured"]},{"year":null,"claim":"How polyglucosan structure forms in the absence of normal priming, and how glycogen-fueled metabolism is mechanistically coupled to inflammatory activation, remain open.","evidence":"","pmids":[],"confidence":"Medium","gaps":["No structural model of glycogenin-1 substrate-binding domain in the corpus","Mechanism linking enzyme loss to abnormal glucan branching unresolved","Pathway connecting myeloid glycogen to cytokine production undefined"]}],"mechanism_profile":{"molecular_activity":[{"term_id":"GO:0016740","term_label":"transferase activity","supporting_discovery_ids":[0,1,2]}],"localization":[],"pathway":[{"term_id":"R-HSA-1430728","term_label":"Metabolism","supporting_discovery_ids":[0,3,4]}],"complexes":[],"partners":[],"other_free_text":[]}},"prefetch_data":{"uniprot":{"accession":"P46976","full_name":"Glycogenin-1","aliases":[],"length_aa":350,"mass_kda":39.4,"function":"Glycogenin participates in the glycogen biosynthetic process along with glycogen synthase and glycogen branching enzyme. It catalyzes the formation of a short alpha (1,4)-glucosyl chain covalently attached via a glucose 1-O-tyrosyl linkage to internal tyrosine residues and these chains act as primers for the elongation reaction catalyzed by glycogen synthase","subcellular_location":"Cytoplasm; Nucleus","url":"https://www.uniprot.org/uniprotkb/P46976/entry"},"depmap":{"release":"DepMap","has_data":true,"is_common_essential":false,"resolved_as":"","url":"https://depmap.org/portal/gene/GYG1","classification":"Not Classified","n_dependent_lines":1,"n_total_lines":1208,"dependency_fraction":0.0008278145695364238},"opencell":{"profiled":true,"resolved_as":"","ensg_id":"ENSG00000163754","cell_line_id":"CID001593","localizations":[{"compartment":"cytoplasmic","grade":3}],"interactors":[{"gene":"SRP9","stoichiometry":10.0},{"gene":"GYS1","stoichiometry":10.0},{"gene":"GYG2","stoichiometry":10.0},{"gene":"SRP14","stoichiometry":10.0},{"gene":"WDR26","stoichiometry":0.2},{"gene":"SOX12","stoichiometry":0.2}],"url":"https://opencell.sf.czbiohub.org/target/CID001593","total_profiled":1310},"omim":[{"mim_id":"616199","title":"POLYGLUCOSAN BODY MYOPATHY 2; PGBM2","url":"https://www.omim.org/entry/616199"},{"mim_id":"615895","title":"POLYGLUCOSAN BODY MYOPATHY 1 WITH OR WITHOUT IMMUNODEFICIENCY; PGBM1","url":"https://www.omim.org/entry/615895"},{"mim_id":"613507","title":"GLYCOGEN STORAGE DISEASE XV; GSD15","url":"https://www.omim.org/entry/613507"},{"mim_id":"605229","title":"SPASTIC PARAPLEGIA 14, AUTOSOMAL RECESSIVE; SPG14","url":"https://www.omim.org/entry/605229"},{"mim_id":"603942","title":"GLYCOGENIN 1; GYG1","url":"https://www.omim.org/entry/603942"}],"hpa":{"profiled":true,"resolved_as":"","reliability":"Approved","locations":[{"location":"Vesicles","reliability":"Approved"}],"tissue_specificity":"Tissue enhanced","tissue_distribution":"Detected in all","driving_tissues":[{"tissue":"skeletal muscle","ntpm":535.2},{"tissue":"tongue","ntpm":333.9}],"url":"https://www.proteinatlas.org/search/GYG1"},"hgnc":{"alias_symbol":[],"prev_symbol":["GYG"]},"alphafold":{"accession":"P46976","domains":[{"cath_id":"3.90.550.10","chopping":"5-265","consensus_level":"high","plddt":91.1941,"start":5,"end":265},{"cath_id":"-","chopping":"276-301","consensus_level":"medium","plddt":48.5662,"start":276,"end":301},{"cath_id":"-","chopping":"319-350","consensus_level":"high","plddt":79.4431,"start":319,"end":350}],"viewer_url":"https://alphafold.ebi.ac.uk/entry/P46976","model_url":"https://alphafold.ebi.ac.uk/files/AF-P46976-F1-model_v6.cif","pae_url":"https://alphafold.ebi.ac.uk/files/AF-P46976-F1-predicted_aligned_error_v6.png","plddt_mean":84.31},"mouse_models":{"mgi_url":"https://www.informatics.jax.org/marker/summary?nomen=GYG1","jax_strain_url":"https://www.jax.org/strain/search?query=GYG1"},"sequence":{"accession":"P46976","fasta_url":"https://rest.uniprot.org/uniprotkb/P46976.fasta","uniprot_url":"https://www.uniprot.org/uniprotkb/P46976/entry","alphafold_viewer_url":"https://alphafold.ebi.ac.uk/entry/P46976"}},"corpus_meta":[{"pmid":"26652229","id":"PMC_26652229","title":"Late-onset polyglucosan body myopathy in five patients with a homozygous mutation in GYG1.","date":"2015","source":"Neuromuscular disorders : NMD","url":"https://pubmed.ncbi.nlm.nih.gov/26652229","citation_count":25,"is_preprint":false},{"pmid":"27066558","id":"PMC_27066558","title":"GYG1 gene mutations in a family with polyglucosan body myopathy.","date":"2015","source":"Neurology. Genetics","url":"https://pubmed.ncbi.nlm.nih.gov/27066558","citation_count":17,"is_preprint":false},{"pmid":"29143313","id":"PMC_29143313","title":"Polyglucosan myopathy and functional characterization of a novel GYG1 mutation.","date":"2017","source":"Acta neurologica Scandinavica","url":"https://pubmed.ncbi.nlm.nih.gov/29143313","citation_count":14,"is_preprint":false},{"pmid":"29264399","id":"PMC_29264399","title":"Clinical heterogeneity and phenotype/genotype findings in 5 families with GYG1 deficiency.","date":"2017","source":"Neurology. Genetics","url":"https://pubmed.ncbi.nlm.nih.gov/29264399","citation_count":12,"is_preprint":false},{"pmid":"31791869","id":"PMC_31791869","title":"Functional characterization of GYG1 variants in two patients with myopathy and glycogenin-1 deficiency.","date":"2019","source":"Neuromuscular disorders : NMD","url":"https://pubmed.ncbi.nlm.nih.gov/31791869","citation_count":11,"is_preprint":false},{"pmid":"23999308","id":"PMC_23999308","title":"Structure of the red fluorescent protein from a lancelet (Branchiostoma lanceolatum): a novel GYG chromophore covalently bound to a nearby tyrosine.","date":"2013","source":"Acta crystallographica. Section D, Biological crystallography","url":"https://pubmed.ncbi.nlm.nih.gov/23999308","citation_count":9,"is_preprint":false},{"pmid":"29422440","id":"PMC_29422440","title":"GYG1 causing progressive limb girdle myopathy with onset during teenage years (polyglucosan body myopathy 2).","date":"2018","source":"Neuromuscular disorders : NMD","url":"https://pubmed.ncbi.nlm.nih.gov/29422440","citation_count":6,"is_preprint":false},{"pmid":"33257366","id":"PMC_33257366","title":"Sequential spontaneous compartment syndrome in multiple limbs in a young adult with GYG1 gene mutation.","date":"2020","source":"BMJ case reports","url":"https://pubmed.ncbi.nlm.nih.gov/33257366","citation_count":3,"is_preprint":false},{"pmid":"41333476","id":"PMC_41333476","title":"Comprehensive analysis of metabolism-related genes in sepsis reveals metabolic-immune heterogeneity and highlights GYG1 as a potential therapeutic target.","date":"2025","source":"Frontiers in immunology","url":"https://pubmed.ncbi.nlm.nih.gov/41333476","citation_count":1,"is_preprint":false},{"pmid":"42023422","id":"PMC_42023422","title":"Unmasking Compound Heterozygosity in GYG1 Myopathy: Diagnostic Insights From RNA-Seq and Long-Read Genomics.","date":"2026","source":"Clinical genetics","url":"https://pubmed.ncbi.nlm.nih.gov/42023422","citation_count":0,"is_preprint":false},{"pmid":"42165248","id":"PMC_42165248","title":"Dysregulation of glycogen metabolism in cardiomyopathy caused by glycogenin-1 (GYG1) missense variants.","date":"2026","source":"The Journal of clinical endocrinology and metabolism","url":"https://pubmed.ncbi.nlm.nih.gov/42165248","citation_count":0,"is_preprint":false},{"pmid":"41634531","id":"PMC_41634531","title":"GYG1 as a Dual Biomarker of Glucagon-Like Peptide-1 Receptor Agonist Weight-Loss Response: Findings from an Integrative Multi-Omics Substudy of a Phase II Trial.","date":"2026","source":"Endocrinology and metabolism (Seoul, Korea)","url":"https://pubmed.ncbi.nlm.nih.gov/41634531","citation_count":0,"is_preprint":false}],"cost":{"stage1":{"model":"claude-sonnet-4-6","input_tokens":8131,"output_tokens":1549,"usd":0.023814,"stage1_stop_reason":"end_turn"},"stage2":{"model":"claude-opus-4-8","input_tokens":8356,"output_tokens":2507,"usd":0.052228,"stage2_stop_reason":"end_turn"},"total_usd":0.076042,"stage1_batch_id":"msgbatch_01DUPACZi7AAWwuZiUjseQF4","stage2_batch_id":"msgbatch_018yt7chE3f48PEFtDwtj6AE","note":"batch pricing = 50% of standard"},"stage1_raw":"```json\n{\n  \"discoveries\": [\n    {\n      \"year\": 2017,\n      \"finding\": \"A novel GYG1 missense mutation (c.403G>A; p.Gly135Arg) located in the substrate binding domain abolishes the enzymatic autoglucosylation function of glycogenin-1, as demonstrated by an in vitro autoglucosylation assay. The mutation also caused reduced expression of glycogenin-1 protein.\",\n      \"method\": \"In vitro autoglucosylation assay; protein expression analysis of patient muscle tissue\",\n      \"journal\": \"Acta neurologica Scandinavica\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 1 / Weak — direct in vitro enzymatic assay with mutant protein, single lab, single study\",\n      \"pmids\": [\"29143313\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2019,\n      \"finding\": \"Loss-of-function variants in GYG1 (including splice acceptor, frameshift, and missense variants) result in either total absence or reduced expression of glycogenin-1 protein, and residual mutant protein (p.Asp102His) is non-functional, leading to glycogen and polyglucosan storage in skeletal muscle fibers.\",\n      \"method\": \"Protein expression analysis (Western blot) of patient muscle biopsies; PAS staining and electron microscopy of muscle; functional inference from variant type\",\n      \"journal\": \"Neuromuscular disorders : NMD\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — protein analysis with multiple patients, two orthogonal morphological methods, single lab\",\n      \"pmids\": [\"31791869\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2017,\n      \"finding\": \"GYG1 mutations causing loss or reduction of glycogenin-1 expression result in impaired glucosylation activity, as shown by protein analysis of patient muscle biopsies revealing either absence of glycogenin-1 or reduced expression with impaired glucosylation.\",\n      \"method\": \"Protein analysis of patient muscle biopsies (Western blot/immunohistochemistry); direct sequencing and exome sequencing for variant identification\",\n      \"journal\": \"Neurology. Genetics\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — multiple families, protein-level functional readout, replicated across multiple patients and labs\",\n      \"pmids\": [\"29264399\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2026,\n      \"finding\": \"In GSD15 (GYG1 cardiomyopathy), storage material in cardiomyocytes is enriched in proteins involved in glycogen metabolism (glycogen synthase, UDP-glucose pyrophosphorylase 2, glycogenin-1, glycogen phosphorylase, glycogen debranching enzyme), as well as sequestosome 1 (p62) and desmin, without evidence of increased autophagocytosis. Whole-tissue proteomics revealed upregulation of cardiomyopathy biomarkers and downregulation of mitochondrial proteins, indicating impaired energy metabolism.\",\n      \"method\": \"Laser capture microdissection followed by quantitative mass spectrometry; immunohistochemistry; whole-tissue quantitative mass spectrometry of patient heart explants vs. controls\",\n      \"journal\": \"The Journal of clinical endocrinology and metabolism\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — multiple orthogonal methods (LCM-MS, IHC, whole-tissue MS) in patient tissue, single lab\",\n      \"pmids\": [\"42165248\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2025,\n      \"finding\": \"In vivo knockdown of Gyg1 via LNP-mediated siRNA delivery in an LPS-induced sepsis mouse model significantly reduced glycogen content in myeloid cells, attenuated IL-6 and TNF-α production, alleviated LPS-induced neutrophilia, and modestly decreased CD40 expression in monocytes and dendritic cells, improving survival.\",\n      \"method\": \"LNP-mediated siRNA knockdown in vivo (LPS mouse model); glycogen content measurement; cytokine assays; flow cytometry\",\n      \"journal\": \"Frontiers in immunology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Weak — in vivo loss-of-function with defined cellular phenotype, single lab, single study\",\n      \"pmids\": [\"41333476\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2026,\n      \"finding\": \"RNA sequencing of patient muscle confirmed that the GYG1 splice-site variant c.143+3G>C causes exon 2 skipping, and the deep intronic variant c.7+992T>G activates a cryptic exon insertion, both leading to aberrant GYG1 transcripts. Long-read genome sequencing established that these two variants are in trans (compound heterozygous).\",\n      \"method\": \"RNA sequencing (RNA-seq); long-read genome sequencing; long-range PCR\",\n      \"journal\": \"Clinical genetics\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Weak — RNA-seq and long-read GS directly confirm splicing mechanism, single case, single lab\",\n      \"pmids\": [\"42023422\"],\n      \"is_preprint\": false\n    }\n  ],\n  \"current_model\": \"GYG1 encodes glycogenin-1, the auto-glucosylating primer enzyme required for glycogen synthesis; loss-of-function or enzymatically null mutations (including missense variants in the substrate-binding domain, frameshift, splice-site, and deep intronic variants causing aberrant splicing) abolish autoglucosylation activity, leading to polyglucosan accumulation in skeletal muscle and cardiomyocytes, sequestration of glycogen-metabolism proteins, disruption of mitochondrial and sarcomeric architecture, and—in myeloid cells—metabolic fueling of inflammatory activation that can be attenuated by Gyg1 knockdown.\"\n}\n```","stage2_raw":"{\n  \"mechanistic_narrative\": \"GYG1 encodes glycogenin-1, the auto-glucosylating priming enzyme required for glycogen synthesis, whose loss disrupts glycogen homeostasis across multiple tissues [#0, #2]. Disease-associated variants—including a substrate-binding-domain missense mutation (p.Gly135Arg), additional missense (p.Asp102His), frameshift, splice-acceptor, and deep intronic variants—abolish or reduce glycogenin-1 expression and eliminate autoglucosylation activity, as established directly by in vitro autoglucosylation assays and patient-muscle protein analysis [#0, #1, #2]. Splice-disrupting alleles act through exon 2 skipping and cryptic exon activation, producing aberrant transcripts that can occur in trans as compound heterozygous lesions [#5]. Enzymatic failure leads to accumulation of polyglucosan storage material in skeletal muscle fibers and cardiomyocytes [#1, #3]. In GYG1 cardiomyopathy (GSD15), this storage material sequesters glycogen-metabolism enzymes (glycogen synthase, UDP-glucose pyrophosphorylase 2, glycogenin-1, glycogen phosphorylase, debranching enzyme) along with p62 and desmin, accompanied by downregulation of mitochondrial proteins indicating impaired energy metabolism, without increased autophagy [#3]. Beyond its role in storage disease, glycogenin-1-dependent glycogen supports inflammatory activation of myeloid cells: in vivo Gyg1 knockdown lowers myeloid glycogen, attenuates IL-6 and TNF-\\u03b1 production and neutrophilia, and improves survival in LPS-induced sepsis [#4].\",\n  \"teleology\": [\n    {\n      \"year\": 2017,\n      \"claim\": \"It was unknown whether specific GYG1 missense variants directly impair catalytic function rather than merely correlating with disease; an in vitro assay established that a substrate-binding-domain mutation abolishes autoglucosylation activity.\",\n      \"evidence\": \"In vitro autoglucosylation assay with mutant protein plus patient muscle protein expression analysis\",\n      \"pmids\": [\n        \"29143313\"\n      ],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\n        \"Single variant tested in a single study\",\n        \"Effect on downstream glycogen synthesis not directly measured\",\n        \"No structural data on the substrate-binding domain\"\n      ]\n    },\n    {\n      \"year\": 2017,\n      \"claim\": \"Whether diverse GYG1 mutations converge on a common loss-of-expression/loss-of-glucosylation mechanism was unresolved; protein analysis across multiple families showed absence or reduced glycogenin-1 with impaired glucosylation.\",\n      \"evidence\": \"Western blot/immunohistochemistry of patient muscle biopsies with exome and direct sequencing\",\n      \"pmids\": [\n        \"29264399\"\n      ],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\n        \"Functional inference partly from variant type rather than direct enzymatic assay\",\n        \"Genotype-phenotype correlation across tissues not established\"\n      ]\n    },\n    {\n      \"year\": 2019,\n      \"claim\": \"It was unclear whether residual mutant protein retains function; analysis showed loss-of-function variants yield absent or non-functional glycogenin-1 and drive glycogen/polyglucosan storage in muscle fibers.\",\n      \"evidence\": \"Western blot, PAS staining, and electron microscopy of patient muscle biopsies\",\n      \"pmids\": [\n        \"31791869\"\n      ],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\n        \"Functional status inferred from variant type for several alleles\",\n        \"Mechanism linking enzyme loss to polyglucosan structure not resolved\"\n      ]\n    },\n    {\n      \"year\": 2025,\n      \"claim\": \"Whether glycogenin-1-dependent glycogen has a role beyond storage disease was untested; knockdown showed myeloid glycogen fuels inflammatory cytokine production and that lowering it improves sepsis outcomes.\",\n      \"evidence\": \"LNP-mediated siRNA Gyg1 knockdown in LPS sepsis mouse model with glycogen, cytokine, and flow cytometry readouts\",\n      \"pmids\": [\n        \"41333476\"\n      ],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\n        \"Single in vivo study\",\n        \"Cell-intrinsic vs systemic contribution not dissected\",\n        \"Mechanism linking glycogen to cytokine output not defined\"\n      ]\n    },\n    {\n      \"year\": 2026,\n      \"claim\": \"The composition of cardiac storage material in GYG1 cardiomyopathy was unknown; proteomics revealed enrichment of sequestered glycogen-metabolism enzymes, p62, and desmin alongside mitochondrial protein downregulation.\",\n      \"evidence\": \"Laser capture microdissection mass spectrometry, whole-tissue MS, and immunohistochemistry of patient heart explants vs controls\",\n      \"pmids\": [\n        \"42165248\"\n      ],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\n        \"Single lab, limited patient samples\",\n        \"Causal link between protein sequestration and mitochondrial dysfunction not established\",\n        \"No mechanism for absence of autophagic clearance\"\n      ]\n    },\n    {\n      \"year\": 2026,\n      \"claim\": \"The molecular consequence of non-coding GYG1 variants was uncharacterized; transcript and genome analysis confirmed exon skipping and cryptic exon activation arising from compound heterozygous in-trans alleles.\",\n      \"evidence\": \"RNA-seq, long-read genome sequencing, and long-range PCR of patient material\",\n      \"pmids\": [\n        \"42023422\"\n      ],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\n        \"Single case\",\n        \"Quantitative effect on protein output not measured\"\n      ]\n    },\n    {\n      \"year\": null,\n      \"claim\": \"How polyglucosan structure forms in the absence of normal priming, and how glycogen-fueled metabolism is mechanistically coupled to inflammatory activation, remain open.\",\n      \"evidence\": \"\",\n      \"pmids\": [],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\n        \"No structural model of glycogenin-1 substrate-binding domain in the corpus\",\n        \"Mechanism linking enzyme loss to abnormal glucan branching unresolved\",\n        \"Pathway connecting myeloid glycogen to cytokine production undefined\"\n      ]\n    }\n  ],\n  \"mechanism_profile\": {\n    \"molecular_activity\": [\n      {\n        \"term_id\": \"GO:0016740\",\n        \"supporting_discovery_ids\": [\n          0,\n          1,\n          2\n        ]\n      },\n      {\n        \"term_id\": \"GO:0016757\",\n        \"supporting_discovery_ids\": [\n          0\n        ]\n      }\n    ],\n    \"localization\": [],\n    \"pathway\": [\n      {\n        \"term_id\": \"R-HSA-1430728\",\n        \"supporting_discovery_ids\": [\n          0,\n          3,\n          4\n        ]\n      }\n    ],\n    \"complexes\": [],\n    \"partners\": [],\n    \"other_free_text\": []\n  }\n}","audit_flag":null,"evaluation":{"pairwise":"win","faith_supported":6,"faith_total":6,"faith_pct":100.0}}