{"gene":"GRID2","run_date":"2026-06-10T01:55:21","timeline":{"discoveries":[{"year":1995,"finding":"GluR delta 2 (GRID2) is required for formation of parallel fiber-Purkinje cell synapses and climbing fiber-Purkinje cell synapses in the cerebellum, and for long-term depression of parallel fiber-Purkinje cell synaptic transmission; loss-of-function knockout mice show impaired motor coordination.","method":"Gene targeting (knockout mouse), electrophysiology, histology","journal":"Cell","confidence":"High","confidence_rationale":"Tier 2 / Strong — clean loss-of-function knockout with multiple defined cellular and synaptic phenotypes, foundational study widely replicated","pmids":["7736576"],"is_preprint":false},{"year":1999,"finding":"The Lurcher mutation (A654T) in transmembrane domain III of GRID2 converts the receptor into a constitutively active ion channel, causing persistent membrane depolarization and subsequent apoptotic Purkinje cell death; confirmed by expression in Xenopus oocytes showing large constitutive inward current.","method":"Electrophysiology in Xenopus oocytes, patch-clamp of Purkinje cells, gain-of-function mutation analysis","journal":"Annals of the New York Academy of Sciences","confidence":"High","confidence_rationale":"Tier 1 / Strong — in vitro reconstitution in Xenopus oocytes plus in vivo electrophysiology, replicated in subsequent studies","pmids":["10414327"],"is_preprint":false},{"year":2003,"finding":"Lurcher GRID2-induced Purkinje cell death can be dissociated from constitutive depolarization: in Lurcher/hotfoot heteroallelic mutants (one Lurcher allele, no wild-type GRID2), early massive Purkinje cell death occurs via autophagy activation through the GRID2–nPIST–Beclin1 signaling pathway, independently of depolarization.","method":"Genetic epistasis using Lurcher/hotfoot heteroallelic mutants, histology, immunofluorescence for autophagy markers","journal":"Neuron","confidence":"High","confidence_rationale":"Tier 2 / Strong — genetic dissection with heteroallelic mutants identifying a distinct signaling pathway (GRID2–nPIST–Beclin1), multiple cellular readouts","pmids":["12628171"],"is_preprint":false},{"year":2013,"finding":"GRID2 localizes to Purkinje cell dendritic spines in both developing mouse and human cerebella, consistent with a conserved role in parallel fiber-Purkinje cell synapse organization.","method":"Immunohistochemistry on mouse and human brain specimens","journal":"Neurology","confidence":"Medium","confidence_rationale":"Tier 3 / Moderate — direct localization experiment replicated across two species but no functional manipulation in this study","pmids":["24078737"],"is_preprint":false},{"year":2014,"finding":"GRID2 missense mutations at Ala654 (equivalent to the Lurcher site) and nearby residue Leu656 in the M3 transmembrane domain create constitutively active receptors, producing gain-of-function cerebellar ataxia with semidominant transmission in humans, mirroring the Lurcher mouse mechanism.","method":"Whole-exome sequencing, genetic analysis, clinical electrophysiology inference; functional characterization referenced from prior Lurcher studies","journal":"Neurology","confidence":"Medium","confidence_rationale":"Tier 3 / Moderate — human genetics identifying gain-of-function mutations at a functionally characterized domain, consistent with established Lurcher mechanism but no new in vitro assay in this paper","pmids":["25841024"],"is_preprint":false},{"year":2014,"finding":"GRID2 is expressed in human adult retina and retinal pigment epithelium, as well as in murine retina at multiple developmental stages, indicating a functional role for GRID2 beyond cerebellar Purkinje cells.","method":"Immunohistochemistry, RT-qPCR on human and murine retinal tissue","journal":"Genetics in medicine","confidence":"Medium","confidence_rationale":"Tier 3 / Moderate — direct protein localization by IHC and mRNA quantification in two species, but no functional manipulation","pmids":["25122145"],"is_preprint":false},{"year":2014,"finding":"Grid2 deletion in mice alters NMDA receptor-dependent currents in cerebellar granule cells (patch-clamp showed relatively small but detectable change), and also affects AMPA receptor function, suggesting GRID2 is important for correct NMDA and AMPA receptor signaling in granule cells.","method":"Patch-clamp electrophysiology on cultured granule cells from Grid2-deleted mice, optokinetic response behavioral assay","journal":"Genes","confidence":"Medium","confidence_rationale":"Tier 2 / Weak — direct electrophysiological measurement in KO cells from single study; phenotype is modest and from one lab","pmids":["25513882"],"is_preprint":false},{"year":2024,"finding":"Multiple rare GRID2 variants in the M3 transmembrane domain create constitutively active receptors; pentamidine potently inhibits constitutive currents of the GluD2-T649A variant (IC50 ~50 nM). A GRID1 variant at the predicted Cbln2/Cbln4 interaction site disrupts complex formation between GluD1 and Cbln2; GRID2 M3 domain shows different intolerance to variation compared to GRID1 M3.","method":"Electrophysiology (patch-clamp), biochemical assays (complex formation), site-directed mutagenesis, pharmacological inhibition","journal":"Human molecular genetics","confidence":"High","confidence_rationale":"Tier 1 / Moderate — reconstitution of constitutive activity, mutagenesis, pharmacological rescue, and biochemical complex assay in a single study with multiple orthogonal methods","pmids":["37944084"],"is_preprint":false}],"current_model":"GRID2 encodes the GluD2 ionotropic glutamate receptor subunit selectively expressed in cerebellar Purkinje cell dendritic spines, where it is essential for parallel fiber- and climbing fiber-Purkinje cell synapse formation, long-term depression of synaptic transmission, and motor coordination; the Lurcher gain-of-function mutation (A654T in M3) converts GRID2 into a constitutively open channel causing Purkinje cell depolarization and autophagy-mediated death via a GRID2–nPIST–Beclin1 pathway, while loss-of-function alleles cause cerebellar ataxia through synaptic disorganization."},"narrative":{"mechanistic_narrative":"GRID2 encodes the GluD2 ionotropic glutamate receptor delta subunit that organizes excitatory synapse formation in the cerebellum, where it localizes to Purkinje cell dendritic spines in both mouse and human [PMID:7736576, PMID:24078737]. Loss of GRID2 impairs the formation of both parallel fiber- and climbing fiber-Purkinje cell synapses, abolishes long-term depression of parallel fiber synaptic transmission, and produces motor incoordination [PMID:7736576], and its deletion additionally perturbs NMDA and AMPA receptor signaling in cerebellar granule cells [PMID:25513882]. The Lurcher mutation (A654T) in the M3 transmembrane domain converts the receptor into a constitutively open channel that drives persistent membrane depolarization and Purkinje cell death [PMID:10414327]; this death proceeds at least in part through a depolarization-independent autophagy route engaging the GRID2-nPIST-Beclin1 signaling pathway [PMID:12628171]. Human gain-of-function missense mutations at Ala654 and adjacent M3 residues (Leu656, T649A) recapitulate this constitutive activity and cause semidominant cerebellar ataxia, and the constitutive current of the GluD2-T649A variant is potently blocked by pentamidine [PMID:25841024, PMID:37944084]. GRID2 is also expressed in human and murine retina and retinal pigment epithelium, indicating function beyond Purkinje cells [PMID:25122145].","teleology":[{"year":1995,"claim":"Established that GRID2 is required for cerebellar synapse formation and synaptic plasticity, defining its core role before any channel or signaling mechanism was known.","evidence":"Knockout mouse with electrophysiology and histology","pmids":["7736576"],"confidence":"High","gaps":["Did not resolve whether GRID2 acts as a functional ion channel or a structural synaptic organizer","Molecular partners mediating synapse formation not identified"]},{"year":1999,"claim":"Showed the Lurcher A654T mutation converts GRID2 into a constitutively open channel, linking a single M3 residue to membrane depolarization and Purkinje cell death.","evidence":"Electrophysiology in Xenopus oocytes and patch-clamp of Purkinje cells with gain-of-function mutant","pmids":["10414327"],"confidence":"High","gaps":["Did not establish whether depolarization alone is sufficient to cause cell death","Endogenous ligand or gating mechanism of wild-type receptor not defined"]},{"year":2003,"claim":"Dissociated Lurcher-induced cell death from depolarization by identifying a GRID2-nPIST-Beclin1 autophagy pathway, revealing a non-channel signaling route to neurodegeneration.","evidence":"Genetic epistasis with Lurcher/hotfoot heteroallelic mutants and autophagy marker immunofluorescence","pmids":["12628171"],"confidence":"High","gaps":["Biochemical mechanism by which GRID2 engages nPIST and Beclin1 not detailed","Relative contribution of autophagy versus depolarization-driven death not quantified"]},{"year":2013,"claim":"Confirmed conserved dendritic spine localization of GRID2 in human as well as mouse Purkinje cells, supporting translational relevance of the mouse synaptic model.","evidence":"Immunohistochemistry on mouse and human cerebellar specimens","pmids":["24078737"],"confidence":"Medium","gaps":["No functional manipulation in this study","Did not address sub-spine distribution or partner colocalization"]},{"year":2014,"claim":"Extended GRID2 function beyond the cerebellum by demonstrating expression in retina and retinal pigment epithelium, and showed Grid2 deletion alters granule-cell NMDA and AMPA receptor currents.","evidence":"Immunohistochemistry and RT-qPCR on retinal tissue; patch-clamp on KO granule cells with optokinetic assay","pmids":["25122145","25513882"],"confidence":"Medium","gaps":["Functional role of GRID2 in retina not tested","Magnitude and mechanism of the granule-cell receptor effect modest and from single studies"]},{"year":2014,"claim":"Translated the Lurcher mechanism to human disease by identifying gain-of-function M3 mutations at Ala654 and Leu656 causing semidominant cerebellar ataxia.","evidence":"Whole-exome sequencing and genetic analysis with mechanism inferred from prior Lurcher work","pmids":["25841024"],"confidence":"Medium","gaps":["No new in vitro functional assay of the human variants in this study","Loss-of-function human alleles not characterized here"]},{"year":2024,"claim":"Demonstrated that multiple M3 variants produce constitutive activity and that pentamidine pharmacologically blocks the constitutive current, providing a candidate therapeutic strategy and structure-function map of M3 intolerance.","evidence":"Patch-clamp electrophysiology, site-directed mutagenesis, complex-formation biochemistry, and pharmacological inhibition","pmids":["37944084"],"confidence":"High","gaps":["In vivo efficacy of pentamidine not tested","Endogenous gating ligand of GRID2 remains undefined"]},{"year":null,"claim":"The physiological gating ligand and the molecular basis by which GRID2 organizes presynaptic-postsynaptic contacts remain unresolved.","evidence":"","pmids":[],"confidence":"High","gaps":["No endogenous agonist defined for wild-type GRID2","Structural mechanism of trans-synaptic synapse organization not established in the corpus"]}],"mechanism_profile":{"molecular_activity":[],"localization":[{"term_id":"GO:0005886","term_label":"plasma membrane","supporting_discovery_ids":[3]},{"term_id":"GO:0005886","term_label":"plasma membrane","supporting_discovery_ids":[1]}],"pathway":[{"term_id":"R-HSA-112316","term_label":"Neuronal System","supporting_discovery_ids":[0]},{"term_id":"R-HSA-9612973","term_label":"Autophagy","supporting_discovery_ids":[2]}],"complexes":[],"partners":["NPIST","BECLIN1"],"other_free_text":[]}},"prefetch_data":{"uniprot":{"accession":"O43424","full_name":"Glutamate receptor ionotropic, delta-2","aliases":[],"length_aa":1007,"mass_kda":113.4,"function":"Member of the ionotropic glutamate receptor family, which plays a crucial role in synaptic organization and signal transduction in the central nervous system. Although it shares structural features with ionotropic glutamate receptors, does not bind glutamate as a primary ligand (PubMed:34936451). Promotes synaptogenesis and mediates the D-Serine-dependent long term depression signals and AMPA receptor endocytosis of cerebellar parallel fiber-Purkinje cell (PF-PC) synapses through the NRX1B-CBLN1-GRID2 triad complex (PubMed:27418511). In the presence of neurexins and cerebellins, forms cation-selective channels that are proposed to be gated by glycine and D-serine (PubMed:34936451). However, recent research disputes this ligand-gated cation channel activity (PubMed:39052831). Cation-selective ion channel activity can be triggered by GRM1 in Purkinje cells (PubMed:24357660, PubMed:27276689)","subcellular_location":"Postsynaptic cell membrane","url":"https://www.uniprot.org/uniprotkb/O43424/entry"},"depmap":{"release":"DepMap","has_data":true,"is_common_essential":false,"resolved_as":"","url":"https://depmap.org/portal/gene/GRID2","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/GRID2","total_profiled":1310},"omim":[{"mim_id":"616204","title":"SPINOCEREBELLAR ATAXIA, AUTOSOMAL RECESSIVE 18; SCAR18","url":"https://www.omim.org/entry/616204"},{"mim_id":"615029","title":"PRECEREBELLIN 4; CBLN4","url":"https://www.omim.org/entry/615029"},{"mim_id":"610639","title":"GRID2-INTERACTING PROTEIN 1; GRID2IP1","url":"https://www.omim.org/entry/610639"},{"mim_id":"606845","title":"GOLGI-ASSOCIATED PDZ AND COILED-COIL DOMAINS-CONTAINING PROTEIN; GOPC","url":"https://www.omim.org/entry/606845"},{"mim_id":"604378","title":"BECLIN 1; BECN1","url":"https://www.omim.org/entry/604378"}],"hpa":{"profiled":true,"resolved_as":"","reliability":"","locations":[],"tissue_specificity":"Group enriched","tissue_distribution":"Detected in some","driving_tissues":[{"tissue":"brain","ntpm":10.5},{"tissue":"testis","ntpm":31.7}],"url":"https://www.proteinatlas.org/search/GRID2"},"hgnc":{"alias_symbol":["GluD2","GluR-delta-2"],"prev_symbol":[]},"alphafold":{"accession":"O43424","domains":[{"cath_id":"3.40.50.2300","chopping":"25-149_298-386","consensus_level":"medium","plddt":84.9711,"start":25,"end":386},{"cath_id":"3.40.50.2300","chopping":"152-291_398-428","consensus_level":"medium","plddt":86.1075,"start":152,"end":428},{"cath_id":"3.40.190.10","chopping":"443-544","consensus_level":"medium","plddt":89.6039,"start":443,"end":544},{"cath_id":"3.40.190.10","chopping":"550-554_663-766","consensus_level":"high","plddt":82.6228,"start":550,"end":766},{"cath_id":"1.10.287.70","chopping":"561-594_603-658","consensus_level":"high","plddt":83.155,"start":561,"end":658}],"viewer_url":"https://alphafold.ebi.ac.uk/entry/O43424","model_url":"https://alphafold.ebi.ac.uk/files/AF-O43424-F1-model_v6.cif","pae_url":"https://alphafold.ebi.ac.uk/files/AF-O43424-F1-predicted_aligned_error_v6.png","plddt_mean":75.88},"mouse_models":{"mgi_url":"https://www.informatics.jax.org/marker/summary?nomen=GRID2","jax_strain_url":"https://www.jax.org/strain/search?query=GRID2"},"sequence":{"accession":"O43424","fasta_url":"https://rest.uniprot.org/uniprotkb/O43424.fasta","uniprot_url":"https://www.uniprot.org/uniprotkb/O43424/entry","alphafold_viewer_url":"https://alphafold.ebi.ac.uk/entry/O43424"}},"corpus_meta":[{"pmid":"7736576","id":"PMC_7736576","title":"Impairment of motor coordination, Purkinje cell synapse formation, and cerebellar long-term depression in GluR delta 2 mutant mice.","date":"1995","source":"Cell","url":"https://pubmed.ncbi.nlm.nih.gov/7736576","citation_count":483,"is_preprint":false},{"pmid":"24078737","id":"PMC_24078737","title":"Deletions in GRID2 lead to a recessive syndrome of cerebellar ataxia and tonic upgaze in humans.","date":"2013","source":"Neurology","url":"https://pubmed.ncbi.nlm.nih.gov/24078737","citation_count":81,"is_preprint":false},{"pmid":"12628171","id":"PMC_12628171","title":"Lurcher GRID2-induced death and depolarization can be dissociated in cerebellar Purkinje cells.","date":"2003","source":"Neuron","url":"https://pubmed.ncbi.nlm.nih.gov/12628171","citation_count":66,"is_preprint":false},{"pmid":"25841024","id":"PMC_25841024","title":"GRID2 mutations span from congenital to mild adult-onset cerebellar 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spinocerebellar ataxia 18 caused by homozygous exon 14 duplication in GRID2 and review of the literature.","date":"2020","source":"Acta neurologica Belgica","url":"https://pubmed.ncbi.nlm.nih.gov/32170608","citation_count":12,"is_preprint":false},{"pmid":"25146332","id":"PMC_25146332","title":"GRID2 a novel gene possibly associated with mevalonate kinase deficiency.","date":"2014","source":"Rheumatology international","url":"https://pubmed.ncbi.nlm.nih.gov/25146332","citation_count":11,"is_preprint":false},{"pmid":"31183084","id":"PMC_31183084","title":"Further delineation of the phenotype caused by a novel large homozygous deletion of GRID2 gene in an adult patient.","date":"2019","source":"Clinical case reports","url":"https://pubmed.ncbi.nlm.nih.gov/31183084","citation_count":11,"is_preprint":false},{"pmid":"15674731","id":"PMC_15674731","title":"Two reciprocal translocations provide new clues to the high mutability of the Grid2 locus.","date":"2005","source":"Mammalian genome : official journal of the International Mammalian Genome Society","url":"https://pubmed.ncbi.nlm.nih.gov/15674731","citation_count":10,"is_preprint":false},{"pmid":"25513882","id":"PMC_25513882","title":"Altered Actions of Memantine and NMDA-Induced Currents in a New Grid2-Deleted Mouse Line.","date":"2014","source":"Genes","url":"https://pubmed.ncbi.nlm.nih.gov/25513882","citation_count":9,"is_preprint":false},{"pmid":"29888788","id":"PMC_29888788","title":"Evidence for generative homology of cerebellum and cerebellum-like structures in an elasmobranch fish based on Pax6, Cbln1 and Grid2 expression.","date":"2018","source":"The Journal of comparative neurology","url":"https://pubmed.ncbi.nlm.nih.gov/29888788","citation_count":7,"is_preprint":false},{"pmid":"36162328","id":"PMC_36162328","title":"GRID2 aberration leads to disturbance in neuroactive ligand-receptor interactions via changes to the species richness and composition of gut microbes.","date":"2022","source":"Biochemical and 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\"finding\": \"GluR delta 2 (GRID2) is required for formation of parallel fiber-Purkinje cell synapses and climbing fiber-Purkinje cell synapses in the cerebellum, and for long-term depression of parallel fiber-Purkinje cell synaptic transmission; loss-of-function knockout mice show impaired motor coordination.\",\n      \"method\": \"Gene targeting (knockout mouse), electrophysiology, histology\",\n      \"journal\": \"Cell\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — clean loss-of-function knockout with multiple defined cellular and synaptic phenotypes, foundational study widely replicated\",\n      \"pmids\": [\"7736576\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1999,\n      \"finding\": \"The Lurcher mutation (A654T) in transmembrane domain III of GRID2 converts the receptor into a constitutively active ion channel, causing persistent membrane depolarization and subsequent apoptotic Purkinje cell death; confirmed by expression in Xenopus oocytes showing large constitutive inward current.\",\n      \"method\": \"Electrophysiology in Xenopus oocytes, patch-clamp of Purkinje cells, gain-of-function mutation analysis\",\n      \"journal\": \"Annals of the New York Academy of Sciences\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Strong — in vitro reconstitution in Xenopus oocytes plus in vivo electrophysiology, replicated in subsequent studies\",\n      \"pmids\": [\"10414327\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2003,\n      \"finding\": \"Lurcher GRID2-induced Purkinje cell death can be dissociated from constitutive depolarization: in Lurcher/hotfoot heteroallelic mutants (one Lurcher allele, no wild-type GRID2), early massive Purkinje cell death occurs via autophagy activation through the GRID2–nPIST–Beclin1 signaling pathway, independently of depolarization.\",\n      \"method\": \"Genetic epistasis using Lurcher/hotfoot heteroallelic mutants, histology, immunofluorescence for autophagy markers\",\n      \"journal\": \"Neuron\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — genetic dissection with heteroallelic mutants identifying a distinct signaling pathway (GRID2–nPIST–Beclin1), multiple cellular readouts\",\n      \"pmids\": [\"12628171\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2013,\n      \"finding\": \"GRID2 localizes to Purkinje cell dendritic spines in both developing mouse and human cerebella, consistent with a conserved role in parallel fiber-Purkinje cell synapse organization.\",\n      \"method\": \"Immunohistochemistry on mouse and human brain specimens\",\n      \"journal\": \"Neurology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 3 / Moderate — direct localization experiment replicated across two species but no functional manipulation in this study\",\n      \"pmids\": [\"24078737\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2014,\n      \"finding\": \"GRID2 missense mutations at Ala654 (equivalent to the Lurcher site) and nearby residue Leu656 in the M3 transmembrane domain create constitutively active receptors, producing gain-of-function cerebellar ataxia with semidominant transmission in humans, mirroring the Lurcher mouse mechanism.\",\n      \"method\": \"Whole-exome sequencing, genetic analysis, clinical electrophysiology inference; functional characterization referenced from prior Lurcher studies\",\n      \"journal\": \"Neurology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 3 / Moderate — human genetics identifying gain-of-function mutations at a functionally characterized domain, consistent with established Lurcher mechanism but no new in vitro assay in this paper\",\n      \"pmids\": [\"25841024\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2014,\n      \"finding\": \"GRID2 is expressed in human adult retina and retinal pigment epithelium, as well as in murine retina at multiple developmental stages, indicating a functional role for GRID2 beyond cerebellar Purkinje cells.\",\n      \"method\": \"Immunohistochemistry, RT-qPCR on human and murine retinal tissue\",\n      \"journal\": \"Genetics in medicine\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 3 / Moderate — direct protein localization by IHC and mRNA quantification in two species, but no functional manipulation\",\n      \"pmids\": [\"25122145\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2014,\n      \"finding\": \"Grid2 deletion in mice alters NMDA receptor-dependent currents in cerebellar granule cells (patch-clamp showed relatively small but detectable change), and also affects AMPA receptor function, suggesting GRID2 is important for correct NMDA and AMPA receptor signaling in granule cells.\",\n      \"method\": \"Patch-clamp electrophysiology on cultured granule cells from Grid2-deleted mice, optokinetic response behavioral assay\",\n      \"journal\": \"Genes\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Weak — direct electrophysiological measurement in KO cells from single study; phenotype is modest and from one lab\",\n      \"pmids\": [\"25513882\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2024,\n      \"finding\": \"Multiple rare GRID2 variants in the M3 transmembrane domain create constitutively active receptors; pentamidine potently inhibits constitutive currents of the GluD2-T649A variant (IC50 ~50 nM). A GRID1 variant at the predicted Cbln2/Cbln4 interaction site disrupts complex formation between GluD1 and Cbln2; GRID2 M3 domain shows different intolerance to variation compared to GRID1 M3.\",\n      \"method\": \"Electrophysiology (patch-clamp), biochemical assays (complex formation), site-directed mutagenesis, pharmacological inhibition\",\n      \"journal\": \"Human molecular genetics\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Moderate — reconstitution of constitutive activity, mutagenesis, pharmacological rescue, and biochemical complex assay in a single study with multiple orthogonal methods\",\n      \"pmids\": [\"37944084\"],\n      \"is_preprint\": false\n    }\n  ],\n  \"current_model\": \"GRID2 encodes the GluD2 ionotropic glutamate receptor subunit selectively expressed in cerebellar Purkinje cell dendritic spines, where it is essential for parallel fiber- and climbing fiber-Purkinje cell synapse formation, long-term depression of synaptic transmission, and motor coordination; the Lurcher gain-of-function mutation (A654T in M3) converts GRID2 into a constitutively open channel causing Purkinje cell depolarization and autophagy-mediated death via a GRID2–nPIST–Beclin1 pathway, while loss-of-function alleles cause cerebellar ataxia through synaptic disorganization.\"\n}\n```","stage2_raw":"{\n  \"mechanistic_narrative\": \"GRID2 encodes the GluD2 ionotropic glutamate receptor delta subunit that organizes excitatory synapse formation in the cerebellum, where it localizes to Purkinje cell dendritic spines in both mouse and human [#0, #3]. Loss of GRID2 impairs the formation of both parallel fiber- and climbing fiber-Purkinje cell synapses, abolishes long-term depression of parallel fiber synaptic transmission, and produces motor incoordination [#0], and its deletion additionally perturbs NMDA and AMPA receptor signaling in cerebellar granule cells [#6]. The Lurcher mutation (A654T) in the M3 transmembrane domain converts the receptor into a constitutively open channel that drives persistent membrane depolarization and Purkinje cell death [#1]; this death proceeds at least in part through a depolarization-independent autophagy route engaging the GRID2-nPIST-Beclin1 signaling pathway [#2]. Human gain-of-function missense mutations at Ala654 and adjacent M3 residues (Leu656, T649A) recapitulate this constitutive activity and cause semidominant cerebellar ataxia, and the constitutive current of the GluD2-T649A variant is potently blocked by pentamidine [#4, #7]. GRID2 is also expressed in human and murine retina and retinal pigment epithelium, indicating function beyond Purkinje cells [#5].\",\n  \"teleology\": [\n    {\n      \"year\": 1995,\n      \"claim\": \"Established that GRID2 is required for cerebellar synapse formation and synaptic plasticity, defining its core role before any channel or signaling mechanism was known.\",\n      \"evidence\": \"Knockout mouse with electrophysiology and histology\",\n      \"pmids\": [\"7736576\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Did not resolve whether GRID2 acts as a functional ion channel or a structural synaptic organizer\", \"Molecular partners mediating synapse formation not identified\"]\n    },\n    {\n      \"year\": 1999,\n      \"claim\": \"Showed the Lurcher A654T mutation converts GRID2 into a constitutively open channel, linking a single M3 residue to membrane depolarization and Purkinje cell death.\",\n      \"evidence\": \"Electrophysiology in Xenopus oocytes and patch-clamp of Purkinje cells with gain-of-function mutant\",\n      \"pmids\": [\"10414327\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Did not establish whether depolarization alone is sufficient to cause cell death\", \"Endogenous ligand or gating mechanism of wild-type receptor not defined\"]\n    },\n    {\n      \"year\": 2003,\n      \"claim\": \"Dissociated Lurcher-induced cell death from depolarization by identifying a GRID2-nPIST-Beclin1 autophagy pathway, revealing a non-channel signaling route to neurodegeneration.\",\n      \"evidence\": \"Genetic epistasis with Lurcher/hotfoot heteroallelic mutants and autophagy marker immunofluorescence\",\n      \"pmids\": [\"12628171\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Biochemical mechanism by which GRID2 engages nPIST and Beclin1 not detailed\", \"Relative contribution of autophagy versus depolarization-driven death not quantified\"]\n    },\n    {\n      \"year\": 2013,\n      \"claim\": \"Confirmed conserved dendritic spine localization of GRID2 in human as well as mouse Purkinje cells, supporting translational relevance of the mouse synaptic model.\",\n      \"evidence\": \"Immunohistochemistry on mouse and human cerebellar specimens\",\n      \"pmids\": [\"24078737\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"No functional manipulation in this study\", \"Did not address sub-spine distribution or partner colocalization\"]\n    },\n    {\n      \"year\": 2014,\n      \"claim\": \"Extended GRID2 function beyond the cerebellum by demonstrating expression in retina and retinal pigment epithelium, and showed Grid2 deletion alters granule-cell NMDA and AMPA receptor currents.\",\n      \"evidence\": \"Immunohistochemistry and RT-qPCR on retinal tissue; patch-clamp on KO granule cells with optokinetic assay\",\n      \"pmids\": [\"25122145\", \"25513882\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Functional role of GRID2 in retina not tested\", \"Magnitude and mechanism of the granule-cell receptor effect modest and from single studies\"]\n    },\n    {\n      \"year\": 2014,\n      \"claim\": \"Translated the Lurcher mechanism to human disease by identifying gain-of-function M3 mutations at Ala654 and Leu656 causing semidominant cerebellar ataxia.\",\n      \"evidence\": \"Whole-exome sequencing and genetic analysis with mechanism inferred from prior Lurcher work\",\n      \"pmids\": [\"25841024\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"No new in vitro functional assay of the human variants in this study\", \"Loss-of-function human alleles not characterized here\"]\n    },\n    {\n      \"year\": 2024,\n      \"claim\": \"Demonstrated that multiple M3 variants produce constitutive activity and that pentamidine pharmacologically blocks the constitutive current, providing a candidate therapeutic strategy and structure-function map of M3 intolerance.\",\n      \"evidence\": \"Patch-clamp electrophysiology, site-directed mutagenesis, complex-formation biochemistry, and pharmacological inhibition\",\n      \"pmids\": [\"37944084\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"In vivo efficacy of pentamidine not tested\", \"Endogenous gating ligand of GRID2 remains undefined\"]\n    },\n    {\n      \"year\": null,\n      \"claim\": \"The physiological gating ligand and the molecular basis by which GRID2 organizes presynaptic-postsynaptic contacts remain unresolved.\",\n      \"evidence\": \"\",\n      \"pmids\": [],\n      \"confidence\": \"High\",\n      \"gaps\": [\"No endogenous agonist defined for wild-type GRID2\", \"Structural mechanism of trans-synaptic synapse organization not established in the corpus\"]\n    }\n  ],\n  \"mechanism_profile\": {\n    \"molecular_activity\": [\n      {\"term_id\": \"GO:0005216\", \"supporting_discovery_ids\": [1]}\n    ],\n    \"localization\": [\n      {\"term_id\": \"GO:0005886\", \"supporting_discovery_ids\": [3]},\n      {\"term_id\": \"GO:0005886\", \"supporting_discovery_ids\": [1]}\n    ],\n    \"pathway\": [\n      {\"term_id\": \"R-HSA-112316\", \"supporting_discovery_ids\": [0]},\n      {\"term_id\": \"R-HSA-9612973\", \"supporting_discovery_ids\": [2]}\n    ],\n    \"complexes\": [],\n    \"partners\": [\"nPIST\", \"Beclin1\"],\n    \"other_free_text\": []\n  }\n}","audit_flag":null,"evaluation":{"pairwise":"win","faith_supported":5,"faith_total":5,"faith_pct":100.0}}