{"gene":"AP4M1","run_date":"2026-04-28T17:12:37","timeline":{"discoveries":[{"year":2009,"finding":"AP4M1, encoding the mu subunit of adaptor protein complex-4 (AP-4), is involved in intracellular trafficking of glutamate receptors; loss-of-function mutation in AP4M1 leads to aberrant GluRdelta2 glutamate receptor localization and abnormal dendritic spine morphology in postmortem brain tissue.","method":"Immunohistochemistry and histology on postmortem brain tissue from patients with homozygous splice-site mutation in AP4M1","journal":"American journal of human genetics","confidence":"Medium","confidence_rationale":"Tier 2 — direct immunohistochemical localization of substrate in human tissue with loss-of-function mutation; single study, single method","pmids":["19559397"],"is_preprint":false},{"year":1997,"finding":"AP4M1 (mu-ARP2) is a mu-adaptin-related protein with sequence homology to the medium chains of clathrin coat adaptor complexes, suggesting a role as a subunit of a novel type of clathrin- or non-clathrin-associated protein coat involved in cellular membrane traffic.","method":"cDNA cloning, primary structure analysis, and tissue distribution profiling","journal":"FEBS letters","confidence":"Low","confidence_rationale":"Tier 3 — structural/sequence-based inference of function, no direct functional assay","pmids":["9013859"],"is_preprint":false},{"year":2014,"finding":"AP4M1 protein is localized to dendrites in normal hippocampal neurons but redistributes to axons following oxygen-glucose deprivation, and its expression is downregulated at both mRNA and protein levels after ischemic injury.","method":"Immunofluorescent co-labeling with MAP2 and Tau-1, real-time PCR and western blotting in primary cultured hippocampal neurons subjected to OGD","journal":"Neuroscience letters","confidence":"Low","confidence_rationale":"Tier 3 — direct localization experiment in cultured neurons, but no functional consequence of redistribution was established","pmids":["24486887"],"is_preprint":false},{"year":2023,"finding":"AAV9/AP4M1 gene therapy rescues the loss-of-function phenotype in AP4M1-deficient patient fibroblasts in vitro and in Ap4m1-KO mice in vivo, confirming that AP4M1 is necessary for normal neuronal function and that its restoration is sufficient for phenotypic rescue.","method":"Transduction of patient-derived fibroblasts with AAV2/AP4M1 (in vitro rescue), intrathecal injection of AAV9/AP4M1 in Ap4m1-KO mice with dose- and age-dependent efficacy assessment (in vivo), toxicology studies in WT mice, rats, and non-human primates","journal":"The Journal of clinical investigation","confidence":"High","confidence_rationale":"Tier 1-2 — multiple in vitro and in vivo rescue experiments with dose-response and toxicology in multiple species","pmids":["36951961"],"is_preprint":false},{"year":2020,"finding":"Functional studies in patient-derived fibroblasts with a loss-of-function AP4M1 variant confirmed loss of adaptor protein complex 4 function, establishing AP4M1 as essential for AP-4 complex activity.","method":"Functional studies in patient-derived fibroblasts carrying AP4M1 variant (c.59-1G>C)","journal":"Neurology. Genetics","confidence":"Medium","confidence_rationale":"Tier 2 — direct functional confirmation in patient-derived cells, single lab, single method","pmids":["33553621"],"is_preprint":false}],"current_model":"AP4M1 encodes the mu subunit of the adaptor protein complex-4 (AP-4), which mediates intracellular trafficking of glutamate receptors (including GluRdelta2) in neurons; loss of AP4M1 function disrupts receptor localization, dendritic spine morphology, and axonal trafficking, and its restoration via gene therapy rescues these deficits in cellular and mouse models."},"narrative":{"teleology":[{"year":1997,"claim":"Identification of AP4M1 as a novel mu-adaptin homolog predicted it to function as the medium subunit of a previously unrecognized adaptor protein coat complex involved in vesicular trafficking.","evidence":"cDNA cloning and primary structure analysis with tissue distribution profiling","pmids":["9013859"],"confidence":"Low","gaps":["No functional assay performed; role inferred solely from sequence homology","Whether AP4M1 assembles into a functional adaptor complex was not demonstrated","Cargo specificity unknown"]},{"year":2009,"claim":"Demonstrating that homozygous AP4M1 loss-of-function mutation causes mislocalization of GluRδ2 and aberrant dendritic spines established AP4M1 as essential for neuronal glutamate receptor trafficking and linked it to a Mendelian neurological disorder.","evidence":"Immunohistochemistry and histology on postmortem brain tissue from patients with homozygous splice-site mutation in AP4M1","pmids":["19559397"],"confidence":"Medium","gaps":["Single study based on postmortem tissue; no in vitro reconstitution of AP4M1-dependent trafficking","Whether GluRδ2 is a direct AP-4 cargo or mislocalized secondarily was not resolved","Mechanism by which AP4M1 recognizes cargo sorting signals was not defined"]},{"year":2014,"claim":"Observation that AP4M1 redistributes from dendrites to axons during ischemic stress suggested its trafficking role is dynamically regulated in neurons, though functional consequences remained uncharacterized.","evidence":"Immunofluorescent co-labeling with MAP2 and Tau-1, RT-PCR and western blotting in primary hippocampal neurons subjected to oxygen-glucose deprivation","pmids":["24486887"],"confidence":"Low","gaps":["No functional consequence of redistribution was established","Mechanism driving AP4M1 redistribution under ischemia is unknown","Not independently confirmed in additional models"]},{"year":2020,"claim":"Confirming that a patient-derived AP4M1 loss-of-function variant abolishes AP-4 complex function in fibroblasts established AP4M1 as indispensable for AP-4 assembly or activity.","evidence":"Functional studies in patient-derived fibroblasts carrying AP4M1 c.59-1G>C variant","pmids":["33553621"],"confidence":"Medium","gaps":["Single lab with single method; biochemical basis of complex disruption not detailed","Whether AP-4 complex fails to assemble or assembles but is non-functional was not distinguished"]},{"year":2023,"claim":"AAV-mediated AP4M1 gene replacement rescued defects in patient fibroblasts and Ap4m1-KO mice in a dose- and age-dependent manner, proving that AP4M1 loss is both necessary and sufficient to explain AP-4 deficiency phenotypes.","evidence":"AAV2/AP4M1 transduction of patient fibroblasts (in vitro) and intrathecal AAV9/AP4M1 injection in Ap4m1-KO mice (in vivo) with dose-response, plus toxicology in WT mice, rats, and non-human primates","pmids":["36951961"],"confidence":"High","gaps":["Precise molecular cargoes sorted by reconstituted AP-4 were not identified beyond GluRδ2","Long-term durability of gene therapy rescue in neurons not established","Structural basis for AP4M1 cargo recognition signal binding remains undefined"]},{"year":null,"claim":"The direct cargo recognition mechanism of AP4M1 within the AP-4 complex — including sorting signal specificity, structural basis of substrate binding, and the full spectrum of AP-4-dependent cargoes — remains uncharacterized.","evidence":"","pmids":[],"confidence":"Low","gaps":["No structural model of AP4M1-cargo interaction exists","Full repertoire of AP-4 cargoes beyond GluRδ2 is undefined","Regulation of AP4M1/AP-4 by phosphorylation or other post-translational modifications is unexplored"]}],"mechanism_profile":{"molecular_activity":[{"term_id":"GO:0060090","term_label":"molecular adaptor activity","supporting_discovery_ids":[0,1,4]}],"localization":[{"term_id":"GO:0031410","term_label":"cytoplasmic vesicle","supporting_discovery_ids":[0,1]},{"term_id":"GO:0005829","term_label":"cytosol","supporting_discovery_ids":[2]}],"pathway":[{"term_id":"R-HSA-5653656","term_label":"Vesicle-mediated transport","supporting_discovery_ids":[0,1,4]},{"term_id":"R-HSA-112316","term_label":"Neuronal System","supporting_discovery_ids":[0,2]}],"complexes":["AP-4"],"partners":["GLURDELTA2"],"other_free_text":[]},"mechanistic_narrative":"AP4M1 encodes the mu subunit of adaptor protein complex-4 (AP-4), a heterotetrameric coat complex that mediates intracellular membrane trafficking, particularly of glutamate receptors in neurons [PMID:9013859, PMID:19559397]. Loss-of-function mutations in AP4M1 cause aberrant localization of the GluRδ2 glutamate receptor and abnormal dendritic spine morphology in human brain tissue, establishing its essential role in neuronal receptor sorting [PMID:19559397]. AP4M1 is required for normal AP-4 complex activity, and AAV-mediated gene replacement rescues loss-of-function phenotypes in both patient-derived fibroblasts and Ap4m1-knockout mice, confirming AP4M1 deficiency as the direct cause of AP-4 deficiency syndrome (spastic paraplegia 50) [PMID:33553621, PMID:36951961]."},"prefetch_data":{"uniprot":{"accession":"O00189","full_name":"AP-4 complex subunit mu-1","aliases":["AP-4 adaptor complex mu subunit","Adaptor-related protein complex 4 subunit mu-1","Mu subunit of AP-4","Mu-adaptin-related protein 2","mu-ARP2","Mu4-adaptin","mu4"],"length_aa":453,"mass_kda":50.0,"function":"Component of the adaptor protein complex 4 (AP-4). Adaptor protein complexes are vesicle coat components involved both in vesicle formation and cargo selection. They control the vesicular transport of proteins in different trafficking pathways (PubMed:10066790, PubMed:10436028, PubMed:11139587, PubMed:11802162, PubMed:20230749). AP-4 forms a non clathrin-associated coat on vesicles departing the trans-Golgi network (TGN) and may be involved in the targeting of proteins from the trans-Golgi network (TGN) to the endosomal-lysosomal system (PubMed:11139587, PubMed:20230749). It is also involved in protein sorting to the basolateral membrane in epithelial cells and the proper asymmetric localization of somatodendritic proteins in neurons (By similarity). Within AP-4, the mu-type subunit AP4M1 is directly involved in the recognition and binding of tyrosine-based sorting signals found in the cytoplasmic part of cargos (PubMed:10436028, PubMed:11139587, PubMed:20230749, PubMed:26544806). The adaptor protein complex 4 (AP-4) may also recognize other types of sorting signal (By similarity)","subcellular_location":"Golgi apparatus, trans-Golgi network membrane; Early endosome","url":"https://www.uniprot.org/uniprotkb/O00189/entry"},"depmap":{"release":"DepMap","has_data":true,"is_common_essential":false,"resolved_as":"","url":"https://depmap.org/portal/gene/AP4M1","classification":"Not Classified","n_dependent_lines":2,"n_total_lines":1208,"dependency_fraction":0.0016556291390728477},"opencell":{"profiled":false,"resolved_as":"","ensg_id":"","cell_line_id":"","localizations":[],"interactors":[],"url":"https://opencell.sf.czbiohub.org/search/AP4M1","total_profiled":1310},"omim":[{"mim_id":"620229","title":"FHF COMPLEX SUBUNIT HOOK-INTERACTING PROTEIN 1B; FHIP1B","url":"https://www.omim.org/entry/620229"},{"mim_id":"614066","title":"SPASTIC PARAPLEGIA 47, AUTOSOMAL RECESSIVE; SPG47","url":"https://www.omim.org/entry/614066"},{"mim_id":"613744","title":"SPASTIC PARAPLEGIA 51, AUTOSOMAL RECESSIVE; SPG51","url":"https://www.omim.org/entry/613744"},{"mim_id":"612936","title":"SPASTIC PARAPLEGIA 50, AUTOSOMAL RECESSIVE; SPG50","url":"https://www.omim.org/entry/612936"},{"mim_id":"607825","title":"HOOK MICROTUBULE TETHERING PROTEIN 3; HOOK3","url":"https://www.omim.org/entry/607825"}],"hpa":{"profiled":true,"resolved_as":"","reliability":"","locations":[],"tissue_specificity":"Low tissue specificity","tissue_distribution":"Detected in all","driving_tissues":[],"url":"https://www.proteinatlas.org/search/AP4M1"},"hgnc":{"alias_symbol":["MU-ARP2","MU-4","SPG50"],"prev_symbol":[]},"alphafold":{"accession":"O00189","domains":[{"cath_id":"3.30.450.60","chopping":"5-132","consensus_level":"high","plddt":90.976,"start":5,"end":132},{"cath_id":"2.60.40.1170","chopping":"187-293_416-452","consensus_level":"medium","plddt":87.9642,"start":187,"end":452},{"cath_id":"2.60.40.1170","chopping":"297-384_400-413","consensus_level":"medium","plddt":92.7816,"start":297,"end":413}],"viewer_url":"https://alphafold.ebi.ac.uk/entry/O00189","model_url":"https://alphafold.ebi.ac.uk/files/AF-O00189-F1-model_v6.cif","pae_url":"https://alphafold.ebi.ac.uk/files/AF-O00189-F1-predicted_aligned_error_v6.png","plddt_mean":85.44},"mouse_models":{"mgi_url":"https://www.informatics.jax.org/marker/summary?nomen=AP4M1","jax_strain_url":"https://www.jax.org/strain/search?query=AP4M1"},"sequence":{"accession":"O00189","fasta_url":"https://rest.uniprot.org/uniprotkb/O00189.fasta","uniprot_url":"https://www.uniprot.org/uniprotkb/O00189/entry","alphafold_viewer_url":"https://alphafold.ebi.ac.uk/entry/O00189"}},"corpus_meta":[{"pmid":"2565533","id":"PMC_2565533","title":"The regulated production of mu m and mu s mRNA is dependent on the relative efficiencies of mu s poly(A) site usage and the c mu 4-to-M1 splice.","date":"1989","source":"Molecular and cellular biology","url":"https://pubmed.ncbi.nlm.nih.gov/2565533","citation_count":157,"is_preprint":false},{"pmid":"19559397","id":"PMC_19559397","title":"Mutation in the AP4M1 gene provides a model for neuroaxonal injury in cerebral palsy.","date":"2009","source":"American journal of human genetics","url":"https://pubmed.ncbi.nlm.nih.gov/19559397","citation_count":140,"is_preprint":false},{"pmid":"24700674","id":"PMC_24700674","title":"Autosomal recessive spastic tetraplegia caused by AP4M1 and AP4B1 gene mutation: expansion of the facial and neuroimaging features.","date":"2014","source":"American journal of medical genetics. Part A","url":"https://pubmed.ncbi.nlm.nih.gov/24700674","citation_count":57,"is_preprint":false},{"pmid":"11817937","id":"PMC_11817937","title":"Electronic structure description of the mu(4)-sulfide bridged tetranuclear Cu(Z) center in N(2)O reductase.","date":"2002","source":"Journal of the American Chemical Society","url":"https://pubmed.ncbi.nlm.nih.gov/11817937","citation_count":56,"is_preprint":false},{"pmid":"12197752","id":"PMC_12197752","title":"Spectroscopic and electronic structure studies of the mu(4)-sulfide bridged tetranuclear Cu(Z) cluster in N(2)O reductase: molecular insight into the catalytic mechanism.","date":"2002","source":"Journal of the American Chemical Society","url":"https://pubmed.ncbi.nlm.nih.gov/12197752","citation_count":53,"is_preprint":false},{"pmid":"36951961","id":"PMC_36951961","title":"Intrathecal AAV9/AP4M1 gene therapy for hereditary spastic paraplegia 50 shows safety and efficacy in preclinical studies.","date":"2023","source":"The Journal of clinical investigation","url":"https://pubmed.ncbi.nlm.nih.gov/36951961","citation_count":36,"is_preprint":false},{"pmid":"25496299","id":"PMC_25496299","title":"A novel AP4M1 mutation in autosomal recessive cerebral palsy syndrome and clinical expansion of AP-4 deficiency.","date":"2014","source":"BMC medical genetics","url":"https://pubmed.ncbi.nlm.nih.gov/25496299","citation_count":27,"is_preprint":false},{"pmid":"14203343","id":"PMC_14203343","title":"CALCIUM ION REQUIREMENT FOR PROLIFERATION OF BACTERIOPHAGE PHI MU-4.","date":"1964","source":"Journal of bacteriology","url":"https://pubmed.ncbi.nlm.nih.gov/14203343","citation_count":22,"is_preprint":false},{"pmid":"9013859","id":"PMC_9013859","title":"Identification of two new mu-adaptin-related proteins, mu-ARP1 and mu-ARP2.","date":"1997","source":"FEBS letters","url":"https://pubmed.ncbi.nlm.nih.gov/9013859","citation_count":22,"is_preprint":false},{"pmid":"5874550","id":"PMC_5874550","title":"Isolation and preliminary characterization of bacteriophage phi-mu-4.","date":"1964","source":"Journal of bacteriology","url":"https://pubmed.ncbi.nlm.nih.gov/5874550","citation_count":20,"is_preprint":false},{"pmid":"9317134","id":"PMC_9317134","title":"Domain-switched mouse IgM/IgG2b hybrids indicate individual roles for C mu 2, C mu 3, and C mu 4 domains in the regulation of the interaction of IgM with complement C1q.","date":"1997","source":"Journal of immunology (Baltimore, Md. : 1950)","url":"https://pubmed.ncbi.nlm.nih.gov/9317134","citation_count":15,"is_preprint":false},{"pmid":"28464862","id":"PMC_28464862","title":"Severe congenital microcephaly with AP4M1 mutation, a case report.","date":"2017","source":"BMC medical genetics","url":"https://pubmed.ncbi.nlm.nih.gov/28464862","citation_count":10,"is_preprint":false},{"pmid":"33553621","id":"PMC_33553621","title":"Blended Phenotype of Silver-Russell Syndrome and SPG50 Caused by Maternal Isodisomy of Chromosome 7.","date":"2020","source":"Neurology. 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Section E, Structure reports online","url":"https://pubmed.ncbi.nlm.nih.gov/22346877","citation_count":1,"is_preprint":false},{"pmid":"7734425","id":"PMC_7734425","title":"A monovalent C mu 4-specific ligand enhances the activation of human B cells by membrane IgM cross-linking ligands.","date":"1995","source":"International immunology","url":"https://pubmed.ncbi.nlm.nih.gov/7734425","citation_count":1,"is_preprint":false},{"pmid":"21123880","id":"PMC_21123880","title":"Poly[[tetraaquadi-μ(4)-glutarato-μ(2)-terephthalato-dineodymium(III)] heptadecahydrate].","date":"2010","source":"Acta crystallographica. Section C, Crystal structure communications","url":"https://pubmed.ncbi.nlm.nih.gov/21123880","citation_count":0,"is_preprint":false},{"pmid":"22346806","id":"PMC_22346806","title":"Decacarbon-yl[μ(4)-(ethane-1,2-diyl-dinitrilo)-tetra-kis-(methane-thiol-ato)]bis(triphenyl-phosphane)tetra-iron(2 Fe-Fe).","date":"2012","source":"Acta crystallographica. 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Section C, Crystal structure communications","url":"https://pubmed.ncbi.nlm.nih.gov/22935493","citation_count":0,"is_preprint":false}],"cost":{"stage1":{"model":"claude-sonnet-4-6","input_tokens":12524,"output_tokens":1177,"usd":0.027613},"stage2":{"model":"claude-opus-4-6","input_tokens":4394,"output_tokens":1668,"usd":0.095505},"total_usd":0.123118,"stage1_batch_id":"msgbatch_01TqNM6p6FsoMBT2jzQTwKBr","stage2_batch_id":"msgbatch_01Ya473eco8sTHbvRymQaU8o","note":"batch pricing = 50% of standard"},"stage1_raw":"```json\n{\n  \"discoveries\": [\n    {\n      \"year\": 2009,\n      \"finding\": \"AP4M1, encoding the mu subunit of adaptor protein complex-4 (AP-4), is involved in intracellular trafficking of glutamate receptors; loss-of-function mutation in AP4M1 leads to aberrant GluRdelta2 glutamate receptor localization and abnormal dendritic spine morphology in postmortem brain tissue.\",\n      \"method\": \"Immunohistochemistry and histology on postmortem brain tissue from patients with homozygous splice-site mutation in AP4M1\",\n      \"journal\": \"American journal of human genetics\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — direct immunohistochemical localization of substrate in human tissue with loss-of-function mutation; single study, single method\",\n      \"pmids\": [\"19559397\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1997,\n      \"finding\": \"AP4M1 (mu-ARP2) is a mu-adaptin-related protein with sequence homology to the medium chains of clathrin coat adaptor complexes, suggesting a role as a subunit of a novel type of clathrin- or non-clathrin-associated protein coat involved in cellular membrane traffic.\",\n      \"method\": \"cDNA cloning, primary structure analysis, and tissue distribution profiling\",\n      \"journal\": \"FEBS letters\",\n      \"confidence\": \"Low\",\n      \"confidence_rationale\": \"Tier 3 — structural/sequence-based inference of function, no direct functional assay\",\n      \"pmids\": [\"9013859\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2014,\n      \"finding\": \"AP4M1 protein is localized to dendrites in normal hippocampal neurons but redistributes to axons following oxygen-glucose deprivation, and its expression is downregulated at both mRNA and protein levels after ischemic injury.\",\n      \"method\": \"Immunofluorescent co-labeling with MAP2 and Tau-1, real-time PCR and western blotting in primary cultured hippocampal neurons subjected to OGD\",\n      \"journal\": \"Neuroscience letters\",\n      \"confidence\": \"Low\",\n      \"confidence_rationale\": \"Tier 3 — direct localization experiment in cultured neurons, but no functional consequence of redistribution was established\",\n      \"pmids\": [\"24486887\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2023,\n      \"finding\": \"AAV9/AP4M1 gene therapy rescues the loss-of-function phenotype in AP4M1-deficient patient fibroblasts in vitro and in Ap4m1-KO mice in vivo, confirming that AP4M1 is necessary for normal neuronal function and that its restoration is sufficient for phenotypic rescue.\",\n      \"method\": \"Transduction of patient-derived fibroblasts with AAV2/AP4M1 (in vitro rescue), intrathecal injection of AAV9/AP4M1 in Ap4m1-KO mice with dose- and age-dependent efficacy assessment (in vivo), toxicology studies in WT mice, rats, and non-human primates\",\n      \"journal\": \"The Journal of clinical investigation\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1-2 — multiple in vitro and in vivo rescue experiments with dose-response and toxicology in multiple species\",\n      \"pmids\": [\"36951961\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2020,\n      \"finding\": \"Functional studies in patient-derived fibroblasts with a loss-of-function AP4M1 variant confirmed loss of adaptor protein complex 4 function, establishing AP4M1 as essential for AP-4 complex activity.\",\n      \"method\": \"Functional studies in patient-derived fibroblasts carrying AP4M1 variant (c.59-1G>C)\",\n      \"journal\": \"Neurology. Genetics\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — direct functional confirmation in patient-derived cells, single lab, single method\",\n      \"pmids\": [\"33553621\"],\n      \"is_preprint\": false\n    }\n  ],\n  \"current_model\": \"AP4M1 encodes the mu subunit of the adaptor protein complex-4 (AP-4), which mediates intracellular trafficking of glutamate receptors (including GluRdelta2) in neurons; loss of AP4M1 function disrupts receptor localization, dendritic spine morphology, and axonal trafficking, and its restoration via gene therapy rescues these deficits in cellular and mouse models.\"\n}\n```","stage2_raw":"```json\n{\n  \"mechanistic_narrative\": \"AP4M1 encodes the mu subunit of adaptor protein complex-4 (AP-4), a heterotetrameric coat complex that mediates intracellular membrane trafficking, particularly of glutamate receptors in neurons [PMID:9013859, PMID:19559397]. Loss-of-function mutations in AP4M1 cause aberrant localization of the GluRδ2 glutamate receptor and abnormal dendritic spine morphology in human brain tissue, establishing its essential role in neuronal receptor sorting [PMID:19559397]. AP4M1 is required for normal AP-4 complex activity, and AAV-mediated gene replacement rescues loss-of-function phenotypes in both patient-derived fibroblasts and Ap4m1-knockout mice, confirming AP4M1 deficiency as the direct cause of AP-4 deficiency syndrome (spastic paraplegia 50) [PMID:33553621, PMID:36951961].\",\n  \"teleology\": [\n    {\n      \"year\": 1997,\n      \"claim\": \"Identification of AP4M1 as a novel mu-adaptin homolog predicted it to function as the medium subunit of a previously unrecognized adaptor protein coat complex involved in vesicular trafficking.\",\n      \"evidence\": \"cDNA cloning and primary structure analysis with tissue distribution profiling\",\n      \"pmids\": [\"9013859\"],\n      \"confidence\": \"Low\",\n      \"gaps\": [\n        \"No functional assay performed; role inferred solely from sequence homology\",\n        \"Whether AP4M1 assembles into a functional adaptor complex was not demonstrated\",\n        \"Cargo specificity unknown\"\n      ]\n    },\n    {\n      \"year\": 2009,\n      \"claim\": \"Demonstrating that homozygous AP4M1 loss-of-function mutation causes mislocalization of GluRδ2 and aberrant dendritic spines established AP4M1 as essential for neuronal glutamate receptor trafficking and linked it to a Mendelian neurological disorder.\",\n      \"evidence\": \"Immunohistochemistry and histology on postmortem brain tissue from patients with homozygous splice-site mutation in AP4M1\",\n      \"pmids\": [\"19559397\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\n        \"Single study based on postmortem tissue; no in vitro reconstitution of AP4M1-dependent trafficking\",\n        \"Whether GluRδ2 is a direct AP-4 cargo or mislocalized secondarily was not resolved\",\n        \"Mechanism by which AP4M1 recognizes cargo sorting signals was not defined\"\n      ]\n    },\n    {\n      \"year\": 2014,\n      \"claim\": \"Observation that AP4M1 redistributes from dendrites to axons during ischemic stress suggested its trafficking role is dynamically regulated in neurons, though functional consequences remained uncharacterized.\",\n      \"evidence\": \"Immunofluorescent co-labeling with MAP2 and Tau-1, RT-PCR and western blotting in primary hippocampal neurons subjected to oxygen-glucose deprivation\",\n      \"pmids\": [\"24486887\"],\n      \"confidence\": \"Low\",\n      \"gaps\": [\n        \"No functional consequence of redistribution was established\",\n        \"Mechanism driving AP4M1 redistribution under ischemia is unknown\",\n        \"Not independently confirmed in additional models\"\n      ]\n    },\n    {\n      \"year\": 2020,\n      \"claim\": \"Confirming that a patient-derived AP4M1 loss-of-function variant abolishes AP-4 complex function in fibroblasts established AP4M1 as indispensable for AP-4 assembly or activity.\",\n      \"evidence\": \"Functional studies in patient-derived fibroblasts carrying AP4M1 c.59-1G>C variant\",\n      \"pmids\": [\"33553621\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\n        \"Single lab with single method; biochemical basis of complex disruption not detailed\",\n        \"Whether AP-4 complex fails to assemble or assembles but is non-functional was not distinguished\"\n      ]\n    },\n    {\n      \"year\": 2023,\n      \"claim\": \"AAV-mediated AP4M1 gene replacement rescued defects in patient fibroblasts and Ap4m1-KO mice in a dose- and age-dependent manner, proving that AP4M1 loss is both necessary and sufficient to explain AP-4 deficiency phenotypes.\",\n      \"evidence\": \"AAV2/AP4M1 transduction of patient fibroblasts (in vitro) and intrathecal AAV9/AP4M1 injection in Ap4m1-KO mice (in vivo) with dose-response, plus toxicology in WT mice, rats, and non-human primates\",\n      \"pmids\": [\"36951961\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\n        \"Precise molecular cargoes sorted by reconstituted AP-4 were not identified beyond GluRδ2\",\n        \"Long-term durability of gene therapy rescue in neurons not established\",\n        \"Structural basis for AP4M1 cargo recognition signal binding remains undefined\"\n      ]\n    },\n    {\n      \"year\": null,\n      \"claim\": \"The direct cargo recognition mechanism of AP4M1 within the AP-4 complex — including sorting signal specificity, structural basis of substrate binding, and the full spectrum of AP-4-dependent cargoes — remains uncharacterized.\",\n      \"evidence\": \"\",\n      \"pmids\": [],\n      \"confidence\": \"Low\",\n      \"gaps\": [\n        \"No structural model of AP4M1-cargo interaction exists\",\n        \"Full repertoire of AP-4 cargoes beyond GluRδ2 is undefined\",\n        \"Regulation of AP4M1/AP-4 by phosphorylation or other post-translational modifications is unexplored\"\n      ]\n    }\n  ],\n  \"mechanism_profile\": {\n    \"molecular_activity\": [\n      {\"term_id\": \"GO:0060090\", \"supporting_discovery_ids\": [0, 1, 4]}\n    ],\n    \"localization\": [\n      {\"term_id\": \"GO:0031410\", \"supporting_discovery_ids\": [0, 1]},\n      {\"term_id\": \"GO:0005829\", \"supporting_discovery_ids\": [2]}\n    ],\n    \"pathway\": [\n      {\"term_id\": \"R-HSA-5653656\", \"supporting_discovery_ids\": [0, 1, 4]},\n      {\"term_id\": \"R-HSA-112316\", \"supporting_discovery_ids\": [0, 2]}\n    ],\n    \"complexes\": [\"AP-4\"],\n    \"partners\": [\"GluRdelta2\"],\n    \"other_free_text\": []\n  }\n}\n```"}