{"gene":"AP4M1","run_date":"2026-06-09T22:02:43","timeline":{"discoveries":[{"year":1997,"finding":"AP4M1 (mu-ARP2) was identified as a novel mu-adaptin-related protein homologous to the medium chains of clathrin coat adaptor complexes, sharing 60% identity with mu-ARP1 and 27-31% identity with mu1/mu2-adaptins, suggesting it is a subunit of an uncharacterized non-clathrin protein coat involved in cellular membrane traffic.","method":"cDNA cloning, primary structure analysis, tissue distribution profiling","journal":"FEBS letters","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — direct molecular cloning and sequence analysis with functional inference from homology; single lab, single method, no functional reconstitution","pmids":["9013859"],"is_preprint":false},{"year":2009,"finding":"Loss-of-function mutation in AP4M1 (splice site mutation c.1137+1G>T in intron 14) causes neuroaxonal degeneration with aberrant GluRdelta2 glutamate receptor localization and abnormal dendritic spine morphology, establishing AP4M1's role in intracellular trafficking of glutamate receptors in neurons.","method":"Homozygosity mapping, RNA expression profiling, postmortem brain histology and immunohistochemistry","journal":"American journal of human genetics","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — direct immunohistochemical evidence of aberrant receptor localization in patient postmortem brain; single case study with multiple methods but no functional reconstitution","pmids":["19559397"],"is_preprint":false},{"year":2014,"finding":"AP4M1 protein is normally distributed in the dendrites of hippocampal neurons; following oxygen-glucose deprivation, AP4M1 is downregulated at both mRNA and protein levels and redistributes from dendrites to axons, indicating a role in dendritic compartmentalization that is disrupted by ischemic injury.","method":"Immunofluorescence labeling, real-time PCR, western blotting in oxygen-glucose deprived primary hippocampal neurons","journal":"Neuroscience letters","confidence":"Low","confidence_rationale":"Tier 3 / Weak — single lab, single cell model, correlative localization and expression data without functional rescue or epistasis","pmids":["24486887"],"is_preprint":false},{"year":2021,"finding":"Biallelic loss-of-function variants in AP4M1 (the mu subunit of adaptor protein complex 4) lead to loss of AP-4 complex function, as confirmed by functional studies in patient-derived fibroblasts from SPG50 patients.","method":"iPSC generation, functional characterization of patient-derived fibroblasts (AP-4 function assays)","journal":"Stem cell research","confidence":"Low","confidence_rationale":"Tier 3 / Weak — functional confirmation of loss-of-function in patient cells, but mechanistic details not elaborated in the abstract; single lab","pmids":["34087981"],"is_preprint":false},{"year":2023,"finding":"Transduction of SPG50 patient-derived fibroblasts with AAV2/AP4M1 rescues the AP-4 deficiency phenotype in vitro, and intrathecal delivery of AAV9/AP4M1 in Ap4m1-KO mice achieves dose- and age-dependent functional rescue, establishing that AP4M1 restoration is sufficient to correct AP-4 complex dysfunction.","method":"AAV-mediated gene delivery, in vitro phenotypic rescue in patient fibroblasts, in vivo KO mouse rescue studies, toxicology studies in rats and nonhuman primates","journal":"The Journal of clinical investigation","confidence":"High","confidence_rationale":"Tier 2 / Strong — multiple orthogonal methods (in vitro rescue, in vivo KO rescue, multiple species toxicology), multiple dose groups, replicated across species","pmids":["36951961"],"is_preprint":false},{"year":2020,"finding":"Functional studies in patient-derived fibroblasts with a loss-of-function AP4M1 splice variant (c.59-1G>C) confirmed loss of adaptor protein complex 4 function, supporting AP4M1 as an essential subunit of the AP-4 complex.","method":"Functional studies in patient-derived fibroblasts","journal":"Neurology. Genetics","confidence":"Low","confidence_rationale":"Tier 3 / Weak — functional confirmation in patient cells from a single case report, mechanistic details not elaborated in the abstract","pmids":["33553621"],"is_preprint":false}],"current_model":"AP4M1 encodes the mu subunit of adaptor protein complex 4 (AP-4), a non-clathrin coat complex required for intracellular trafficking of cargo including glutamate receptors (GluRdelta2) in neurons; loss of AP4M1 function disrupts dendritic receptor localization and dendritic spine morphology, and AAV-mediated AP4M1 gene replacement rescues AP-4 complex function both in patient fibroblasts and in Ap4m1-KO mice."},"narrative":{"mechanistic_narrative":"AP4M1 encodes the mu (medium) subunit of a non-clathrin membrane coat adaptor complex, identified by homology to the medium chains of clathrin coat adaptors [PMID:9013859]. In neurons it functions in intracellular trafficking required for dendritic compartmentalization: loss-of-function mutation produces aberrant localization of the GluRdelta2 glutamate receptor, abnormal dendritic spine morphology, and neuroaxonal degeneration [PMID:19559397]. Biallelic loss-of-function variants abolish AP-4 complex function in patient-derived fibroblasts and cause the SPG50 form of hereditary spastic paraplegia [PMID:34087981]. AAV-mediated delivery of AP4M1 restores AP-4 function in patient fibroblasts and achieves functional rescue in Ap4m1-knockout mice, establishing that AP4M1 is an essential, dose-limiting subunit of the complex [PMID:36951961]. Beyond its role as an AP-4 subunit and its neuronal trafficking function, the molecular cargo-recognition mechanism of AP4M1 has not been further characterized in the available corpus.","teleology":[{"year":1997,"claim":"Established AP4M1 as a candidate coat-complex subunit, framing it as a mu-adaptin-related medium chain of a previously uncharacterized non-clathrin protein coat.","evidence":"cDNA cloning, primary structure and homology analysis, tissue distribution profiling","pmids":["9013859"],"confidence":"Medium","gaps":["No demonstration that the protein assembles into a functional complex","No cargo or trafficking substrate identified","Function inferred only from sequence homology"]},{"year":2009,"claim":"Linked AP4M1 loss to a defined neuronal trafficking defect, showing the gene is required for correct localization of a specific glutamate receptor and for dendritic spine architecture.","evidence":"Homozygosity mapping with postmortem brain histology and immunohistochemistry in a patient with a splice-site loss-of-function mutation","pmids":["19559397"],"confidence":"Medium","gaps":["Single case; causality not confirmed by rescue","Mechanism linking AP4M1 to GluRdelta2 trafficking not resolved","No direct cargo-binding evidence"]},{"year":2014,"claim":"Characterized the normal dendritic distribution of AP4M1 and its loss/redistribution under ischemic stress, supporting a role in dendritic compartmentalization.","evidence":"Immunofluorescence, qPCR and western blotting in oxygen-glucose-deprived primary hippocampal neurons","pmids":["24486887"],"confidence":"Low","gaps":["Correlative localization data without functional rescue or epistasis","Single cell model","Does not establish trafficking mechanism"]},{"year":2020,"claim":"Confirmed in independent patient cells that AP4M1 loss-of-function abolishes AP-4 complex function, reinforcing AP4M1 as an essential subunit.","evidence":"Functional studies in patient-derived fibroblasts carrying a splice variant","pmids":["33553621"],"confidence":"Low","gaps":["Single case report; mechanistic detail limited","AP-4 function readout not specified","No structural or cargo-level mechanism"]},{"year":2021,"claim":"Provided further functional confirmation that biallelic AP4M1 variants cause loss of AP-4 function in SPG50 patient cells and generated iPSC resources for the disease.","evidence":"iPSC generation and functional characterization of patient-derived fibroblasts","pmids":["34087981"],"confidence":"Low","gaps":["Mechanistic details not elaborated","Single lab","Does not define molecular trafficking step disrupted"]},{"year":2023,"claim":"Demonstrated that restoring AP4M1 is sufficient to correct AP-4 dysfunction, providing causal proof that the gene's product is the limiting determinant of complex function in vitro and in vivo.","evidence":"AAV-mediated gene delivery with in vitro rescue in patient fibroblasts, in vivo rescue in Ap4m1-KO mice, and multi-species toxicology","pmids":["36951961"],"confidence":"High","gaps":["Molecular cargo-recognition mechanism still not defined","Does not resolve which trafficking pathway step AP4M1 controls","Phenotypic readouts of rescue not mechanistically dissected"]},{"year":null,"claim":"The biochemical mechanism by which AP4M1 recognizes cargo and the full set of trafficking substrates handled by the AP-4 complex remain undefined.","evidence":"No discovery in the timeline reconstitutes cargo binding or maps the trafficking route at molecular resolution","pmids":[],"confidence":"Low","gaps":["No structural model of AP4M1 within AP-4","Cargo-sorting motif specificity unknown","Trafficking itinerary (donor/acceptor compartments) uncharacterized in this corpus"]}],"mechanism_profile":{"molecular_activity":[{"term_id":"GO:0060090","term_label":"molecular adaptor activity","supporting_discovery_ids":[0,1]}],"localization":[],"pathway":[{"term_id":"R-HSA-5653656","term_label":"Vesicle-mediated transport","supporting_discovery_ids":[1,4]}],"complexes":["AP-4 adaptor complex"],"partners":[],"other_free_text":[]}},"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":141,"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":"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":"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":"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. Genetics","url":"https://pubmed.ncbi.nlm.nih.gov/33553621","citation_count":9,"is_preprint":false},{"pmid":"24486887","id":"PMC_24486887","title":"AP4M1 is abnormally expressed in oxygen-glucose deprived hippocampal neurons.","date":"2014","source":"Neuroscience letters","url":"https://pubmed.ncbi.nlm.nih.gov/24486887","citation_count":5,"is_preprint":false},{"pmid":"37758467","id":"PMC_37758467","title":"Identification of novel homozygous variants in FOXE3 and AP4M1 underlying congenital syndromic anophthalmia and microphthalmia.","date":"2023","source":"The journal of gene medicine","url":"https://pubmed.ncbi.nlm.nih.gov/37758467","citation_count":4,"is_preprint":false},{"pmid":"34087981","id":"PMC_34087981","title":"Generation and characterization of six human induced pluripotent stem cell lines (iPSC) from three families with AP4M1-associated hereditary spastic paraplegia (SPG50).","date":"2021","source":"Stem cell research","url":"https://pubmed.ncbi.nlm.nih.gov/34087981","citation_count":4,"is_preprint":false},{"pmid":"22346877","id":"PMC_22346877","title":"catena-Poly[[[bis-[μ-3-(4-carb-oxy-phen-oxy)propionato]-κO,O:O;κO:O,O-bis-[aqua-(N,N-dimethyl-formamide-κO)cadmium]]-μ-4,4'-bipyridine-κN:N'] dinitrate].","date":"2012","source":"Acta crystallographica. 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. Section E, Structure reports online","url":"https://pubmed.ncbi.nlm.nih.gov/22346806","citation_count":0,"is_preprint":false},{"pmid":"41625348","id":"PMC_41625348","title":"A Novel AP4M1 Variant in an Iranian Child with Spastic Paraplegia 50: A Case Report and Molecular Docking Approach.","date":"2026","source":"Iranian journal of medical sciences","url":"https://pubmed.ncbi.nlm.nih.gov/41625348","citation_count":0,"is_preprint":false},{"pmid":"24096493","id":"PMC_24096493","title":"The double-stranded ladder-like structure of poly[[bis(μ2-acetato-κ(2)O:O')bis(acetato-κO)bis(μ-4,4'-bipyridine-κ(2)N:N')dicopper(II)] 4-nitrophenol disolvate tetrahydrate].","date":"2013","source":"Acta crystallographica. Section C, Crystal structure communications","url":"https://pubmed.ncbi.nlm.nih.gov/24096493","citation_count":0,"is_preprint":false},{"pmid":"22935493","id":"PMC_22935493","title":"μ-4,4'-Bipyridine-κ2N:N'-bis[tetraaqua(4,4'-bipyridine-κN)dimanganese(II)] bis(4-aminobenzoate) bis(perchlorate)-4,4'-bipyridine-water (1/2/4): a supramolecular system constructed by π-π and hydrogen-bond interactions.","date":"2012","source":"Acta crystallographica. 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":13293,"output_tokens":1450,"usd":0.030815,"stage1_stop_reason":"end_turn"},"stage2":{"model":"claude-opus-4-8","input_tokens":8179,"output_tokens":2080,"usd":0.046448,"stage2_stop_reason":"end_turn"},"total_usd":0.077263,"stage1_batch_id":"msgbatch_0179Z2pxRYBsXi2xADneafRw","stage2_batch_id":"msgbatch_01LaY9ZaVdgjWArcZo9eqQE5","note":"batch pricing = 50% of standard"},"stage1_raw":"```json\n{\n  \"discoveries\": [\n    {\n      \"year\": 1997,\n      \"finding\": \"AP4M1 (mu-ARP2) was identified as a novel mu-adaptin-related protein homologous to the medium chains of clathrin coat adaptor complexes, sharing 60% identity with mu-ARP1 and 27-31% identity with mu1/mu2-adaptins, suggesting it is a subunit of an uncharacterized non-clathrin protein coat involved in cellular membrane traffic.\",\n      \"method\": \"cDNA cloning, primary structure analysis, tissue distribution profiling\",\n      \"journal\": \"FEBS letters\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — direct molecular cloning and sequence analysis with functional inference from homology; single lab, single method, no functional reconstitution\",\n      \"pmids\": [\"9013859\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2009,\n      \"finding\": \"Loss-of-function mutation in AP4M1 (splice site mutation c.1137+1G>T in intron 14) causes neuroaxonal degeneration with aberrant GluRdelta2 glutamate receptor localization and abnormal dendritic spine morphology, establishing AP4M1's role in intracellular trafficking of glutamate receptors in neurons.\",\n      \"method\": \"Homozygosity mapping, RNA expression profiling, postmortem brain histology and immunohistochemistry\",\n      \"journal\": \"American journal of human genetics\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — direct immunohistochemical evidence of aberrant receptor localization in patient postmortem brain; single case study with multiple methods but no functional reconstitution\",\n      \"pmids\": [\"19559397\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2014,\n      \"finding\": \"AP4M1 protein is normally distributed in the dendrites of hippocampal neurons; following oxygen-glucose deprivation, AP4M1 is downregulated at both mRNA and protein levels and redistributes from dendrites to axons, indicating a role in dendritic compartmentalization that is disrupted by ischemic injury.\",\n      \"method\": \"Immunofluorescence labeling, real-time PCR, western blotting in oxygen-glucose deprived primary hippocampal neurons\",\n      \"journal\": \"Neuroscience letters\",\n      \"confidence\": \"Low\",\n      \"confidence_rationale\": \"Tier 3 / Weak — single lab, single cell model, correlative localization and expression data without functional rescue or epistasis\",\n      \"pmids\": [\"24486887\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2021,\n      \"finding\": \"Biallelic loss-of-function variants in AP4M1 (the mu subunit of adaptor protein complex 4) lead to loss of AP-4 complex function, as confirmed by functional studies in patient-derived fibroblasts from SPG50 patients.\",\n      \"method\": \"iPSC generation, functional characterization of patient-derived fibroblasts (AP-4 function assays)\",\n      \"journal\": \"Stem cell research\",\n      \"confidence\": \"Low\",\n      \"confidence_rationale\": \"Tier 3 / Weak — functional confirmation of loss-of-function in patient cells, but mechanistic details not elaborated in the abstract; single lab\",\n      \"pmids\": [\"34087981\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2023,\n      \"finding\": \"Transduction of SPG50 patient-derived fibroblasts with AAV2/AP4M1 rescues the AP-4 deficiency phenotype in vitro, and intrathecal delivery of AAV9/AP4M1 in Ap4m1-KO mice achieves dose- and age-dependent functional rescue, establishing that AP4M1 restoration is sufficient to correct AP-4 complex dysfunction.\",\n      \"method\": \"AAV-mediated gene delivery, in vitro phenotypic rescue in patient fibroblasts, in vivo KO mouse rescue studies, toxicology studies in rats and nonhuman primates\",\n      \"journal\": \"The Journal of clinical investigation\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — multiple orthogonal methods (in vitro rescue, in vivo KO rescue, multiple species toxicology), multiple dose groups, replicated across 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 splice variant (c.59-1G>C) confirmed loss of adaptor protein complex 4 function, supporting AP4M1 as an essential subunit of the AP-4 complex.\",\n      \"method\": \"Functional studies in patient-derived fibroblasts\",\n      \"journal\": \"Neurology. Genetics\",\n      \"confidence\": \"Low\",\n      \"confidence_rationale\": \"Tier 3 / Weak — functional confirmation in patient cells from a single case report, mechanistic details not elaborated in the abstract\",\n      \"pmids\": [\"33553621\"],\n      \"is_preprint\": false\n    }\n  ],\n  \"current_model\": \"AP4M1 encodes the mu subunit of adaptor protein complex 4 (AP-4), a non-clathrin coat complex required for intracellular trafficking of cargo including glutamate receptors (GluRdelta2) in neurons; loss of AP4M1 function disrupts dendritic receptor localization and dendritic spine morphology, and AAV-mediated AP4M1 gene replacement rescues AP-4 complex function both in patient fibroblasts and in Ap4m1-KO mice.\"\n}\n```","stage2_raw":"{\n  \"mechanistic_narrative\": \"AP4M1 encodes the mu (medium) subunit of a non-clathrin membrane coat adaptor complex, identified by homology to the medium chains of clathrin coat adaptors [#0]. In neurons it functions in intracellular trafficking required for dendritic compartmentalization: loss-of-function mutation produces aberrant localization of the GluRdelta2 glutamate receptor, abnormal dendritic spine morphology, and neuroaxonal degeneration [#1]. Biallelic loss-of-function variants abolish AP-4 complex function in patient-derived fibroblasts and cause the SPG50 form of hereditary spastic paraplegia [#3]. AAV-mediated delivery of AP4M1 restores AP-4 function in patient fibroblasts and achieves functional rescue in Ap4m1-knockout mice, establishing that AP4M1 is an essential, dose-limiting subunit of the complex [#4]. Beyond its role as an AP-4 subunit and its neuronal trafficking function, the molecular cargo-recognition mechanism of AP4M1 has not been further characterized in the available corpus.\",\n  \"teleology\": [\n    {\n      \"year\": 1997,\n      \"claim\": \"Established AP4M1 as a candidate coat-complex subunit, framing it as a mu-adaptin-related medium chain of a previously uncharacterized non-clathrin protein coat.\",\n      \"evidence\": \"cDNA cloning, primary structure and homology analysis, tissue distribution profiling\",\n      \"pmids\": [\"9013859\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"No demonstration that the protein assembles into a functional complex\", \"No cargo or trafficking substrate identified\", \"Function inferred only from sequence homology\"]\n    },\n    {\n      \"year\": 2009,\n      \"claim\": \"Linked AP4M1 loss to a defined neuronal trafficking defect, showing the gene is required for correct localization of a specific glutamate receptor and for dendritic spine architecture.\",\n      \"evidence\": \"Homozygosity mapping with postmortem brain histology and immunohistochemistry in a patient with a splice-site loss-of-function mutation\",\n      \"pmids\": [\"19559397\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Single case; causality not confirmed by rescue\", \"Mechanism linking AP4M1 to GluRdelta2 trafficking not resolved\", \"No direct cargo-binding evidence\"]\n    },\n    {\n      \"year\": 2014,\n      \"claim\": \"Characterized the normal dendritic distribution of AP4M1 and its loss/redistribution under ischemic stress, supporting a role in dendritic compartmentalization.\",\n      \"evidence\": \"Immunofluorescence, qPCR and western blotting in oxygen-glucose-deprived primary hippocampal neurons\",\n      \"pmids\": [\"24486887\"],\n      \"confidence\": \"Low\",\n      \"gaps\": [\"Correlative localization data without functional rescue or epistasis\", \"Single cell model\", \"Does not establish trafficking mechanism\"]\n    },\n    {\n      \"year\": 2020,\n      \"claim\": \"Confirmed in independent patient cells that AP4M1 loss-of-function abolishes AP-4 complex function, reinforcing AP4M1 as an essential subunit.\",\n      \"evidence\": \"Functional studies in patient-derived fibroblasts carrying a splice variant\",\n      \"pmids\": [\"33553621\"],\n      \"confidence\": \"Low\",\n      \"gaps\": [\"Single case report; mechanistic detail limited\", \"AP-4 function readout not specified\", \"No structural or cargo-level mechanism\"]\n    },\n    {\n      \"year\": 2021,\n      \"claim\": \"Provided further functional confirmation that biallelic AP4M1 variants cause loss of AP-4 function in SPG50 patient cells and generated iPSC resources for the disease.\",\n      \"evidence\": \"iPSC generation and functional characterization of patient-derived fibroblasts\",\n      \"pmids\": [\"34087981\"],\n      \"confidence\": \"Low\",\n      \"gaps\": [\"Mechanistic details not elaborated\", \"Single lab\", \"Does not define molecular trafficking step disrupted\"]\n    },\n    {\n      \"year\": 2023,\n      \"claim\": \"Demonstrated that restoring AP4M1 is sufficient to correct AP-4 dysfunction, providing causal proof that the gene's product is the limiting determinant of complex function in vitro and in vivo.\",\n      \"evidence\": \"AAV-mediated gene delivery with in vitro rescue in patient fibroblasts, in vivo rescue in Ap4m1-KO mice, and multi-species toxicology\",\n      \"pmids\": [\"36951961\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Molecular cargo-recognition mechanism still not defined\", \"Does not resolve which trafficking pathway step AP4M1 controls\", \"Phenotypic readouts of rescue not mechanistically dissected\"]\n    },\n    {\n      \"year\": null,\n      \"claim\": \"The biochemical mechanism by which AP4M1 recognizes cargo and the full set of trafficking substrates handled by the AP-4 complex remain undefined.\",\n      \"evidence\": \"No discovery in the timeline reconstitutes cargo binding or maps the trafficking route at molecular resolution\",\n      \"pmids\": [],\n      \"confidence\": \"Low\",\n      \"gaps\": [\"No structural model of AP4M1 within AP-4\", \"Cargo-sorting motif specificity unknown\", \"Trafficking itinerary (donor/acceptor compartments) uncharacterized in this corpus\"]\n    }\n  ],\n  \"mechanism_profile\": {\n    \"molecular_activity\": [\n      {\"term_id\": \"GO:0060090\", \"supporting_discovery_ids\": [0, 1]}\n    ],\n    \"localization\": [],\n    \"pathway\": [\n      {\"term_id\": \"R-HSA-5653656\", \"supporting_discovery_ids\": [1, 4]}\n    ],\n    \"complexes\": [\"AP-4 adaptor complex\"],\n    \"partners\": [],\n    \"other_free_text\": []\n  }\n}","audit_flag":null,"evaluation":{"pairwise":"tie","faith_supported":4,"faith_total":4,"faith_pct":100.0}}