{"gene":"PIGA","run_date":"2026-06-10T06:43:35","timeline":{"discoveries":[{"year":1993,"finding":"PIG-A encodes a protein necessary for the synthesis of N-acetylglucosaminyl-phosphatidylinositol (GlcNAc-PI), the first intermediate in GPI-anchor biosynthesis; complementation of GPI-anchor-deficient cells with PIG-A cDNA restored GPI-anchor synthesis.","method":"cDNA cloning, functional complementation of GPI-deficient cell lines","journal":"Science","confidence":"High","confidence_rationale":"Tier 1 / Strong — direct in vitro/cell-based reconstitution of enzymatic function; founding paper replicated by multiple subsequent groups","pmids":["7680492"],"is_preprint":false},{"year":1996,"finding":"PIG-A is an endoplasmic reticulum transmembrane protein with a large cytoplasmic domain homologous to bacterial GlcNAc transferases and a small lumenal domain; PIG-H is a cytoplasmically oriented ER-associated protein; PIG-A and PIG-H form a protein complex in the ER. The small lumenal domain of PIG-A plays an essential functional role in targeting to the rough ER. GlcNAc transfer to PI occurs on the cytoplasmic face of the ER.","method":"Co-immunoprecipitation, subcellular fractionation, domain deletion/mutagenesis, ER targeting assays","journal":"The Journal of Biological Chemistry","confidence":"High","confidence_rationale":"Tier 1-2 / Strong — multiple orthogonal methods (Co-IP, fractionation, mutagenesis) in a single focused study, subsequently confirmed by the 1998 complex paper","pmids":["8900170"],"is_preprint":false},{"year":1998,"finding":"The first step of GPI biosynthesis (transfer of GlcNAc from UDP-GlcNAc to PI) is catalyzed by a complex of four mammalian proteins—PIG-A, PIG-H, PIG-C, and hGPI1—resident in the ER membrane. The reconstituted complex had GPI-GlcNAc transferase (GPI-GnT) activity in vitro but did not catalyze the second reaction. Bovine PI was utilized ~100-fold more efficiently than soybean PI, indicating that the complex recognizes fatty acyl chains of PI. PIG-L (involved in step 2) did not associate with the isolated complex.","method":"Co-immunoprecipitation, in vitro GlcNAc transferase activity assay, substrate specificity assay with different PI species","journal":"The EMBO Journal","confidence":"High","confidence_rationale":"Tier 1 / Strong — in vitro enzymatic reconstitution plus Co-IP complex identification, multiple orthogonal approaches in one study","pmids":["9463366"],"is_preprint":false},{"year":1994,"finding":"Somatic mutations in PIG-A (frameshift, missense, nonsense, splice site) in hematopoietic cells cause paroxysmal nocturnal hemoglobinuria (PNH); transfection of wild-type PIG-A cDNA into EBV-transformed B-lymphoblastoid cell lines from PNH patients fully restored GPI-linked protein surface expression, proving PIG-A is the causative gene.","method":"RT-PCR/sequencing of PIG-A transcripts, functional complementation transfection assay, flow cytometry","journal":"The EMBO Journal","confidence":"High","confidence_rationale":"Tier 2 / Strong — functional rescue by cDNA complementation plus mutation identification, replicated across multiple independent patient cell lines and subsequent studies","pmids":["8306954"],"is_preprint":false},{"year":1995,"finding":"The yeast GPI3 gene (ortholog of mammalian PIG-A) encodes a protein required for GlcNAc-PI synthesis (first step of GPI anchor biosynthesis); gpi3 mutants lack in vitro GlcNAc-PI synthetic activity; GPI3 is essential for vegetative growth in yeast.","method":"Temperature-sensitive mutant isolation, in vitro [3H]-inositol incorporation assay, gene disruption, genetic complementation","journal":"The Journal of Biological Chemistry","confidence":"High","confidence_rationale":"Tier 1 / Strong — in vitro enzymatic assay plus genetic complementation and gene disruption in yeast ortholog","pmids":["7768896"],"is_preprint":false},{"year":1997,"finding":"Pig-a gene inactivation in mouse embryonic stem cells by homologous recombination produced cells competent for hematopoiesis with the PNH phenotype, but pig-a inactivation alone did not confer a proliferative advantage to hematopoietic stem cells, demonstrating that additional factors are required for PNH clone expansion.","method":"Homologous recombination (gene knockout) in murine ES cells, chimera generation, flow cytometry","journal":"The Journal of Clinical Investigation","confidence":"High","confidence_rationale":"Tier 2 / Strong — clean genetic knockout with defined cellular phenotype readout, replicated in multiple subsequent mouse models","pmids":["9276719"],"is_preprint":false},{"year":1999,"finding":"Cre/loxP-mediated inactivation of Piga in mosaic mice showed that PIGA(-) blood cells are more sensitive to complement-mediated lysis and have a decreased lifespan in circulation, but the PIGA(-) cell population did not expand over 12 months, confirming that Piga mutation alone is insufficient to cause PNH.","method":"Cre/loxP conditional knockout, flow cytometry, complement sensitivity assay, longitudinal monitoring","journal":"Blood","confidence":"High","confidence_rationale":"Tier 2 / Strong — conditional genetic model with multiple functional readouts (complement lysis, lifespan), 12-month longitudinal follow-up","pmids":["10556176"],"is_preprint":false},{"year":1999,"finding":"X chromosome inactivation and somatic cell selection rescue female mice carrying a Piga-null mutation. Tissue analysis showed that most somatic tissues (heart, lung, kidney, brain, liver) preferentially express wild-type Piga, suggesting these tissues require GPI-linked proteins, whereas spleen, thymus, and red blood cells had roughly equal proportions of Piga(+) and Piga(-) cells.","method":"Cre/loxP conditional knockout (EIIa-Cre), tissue fractionation, flow cytometry, X-inactivation analysis","journal":"Proceedings of the National Academy of Sciences","confidence":"High","confidence_rationale":"Tier 2 / Strong — conditional knockout with tissue-level functional consequence, multiple tissues analyzed","pmids":["10377440"],"is_preprint":false},{"year":2001,"finding":"GATA1-Cre-mediated Piga inactivation restricted to the erythroid/megakaryocytic lineage produced mice with up to 100% GPI-deficient red cells; the loss of GPI-linked proteins occurred late in erythroid differentiation, resulting in residual low-level GPI expression resembling PNH type II cells, which showed intermediate complement sensitivity. Recombination was also detected in megakaryocytes, mast cells, and eosinophils but not in neutrophils, lymphocytes, or non-hematopoietic tissues.","method":"GATA1-Cre/loxP conditional knockout, flow cytometry, complement sensitivity assay","journal":"Blood","confidence":"High","confidence_rationale":"Tier 2 / Strong — lineage-specific conditional knockout with defined complement-sensitivity phenotype and cell-type specificity mapping","pmids":["11568013"],"is_preprint":false},{"year":2002,"finding":"PIG-A mutant leukemic cells lacking GPI-anchored proteins showed decreased susceptibility to natural killer (NK) cell killing compared to PIG-A-rescued controls; killing was perforin-dependent (abolished by concanamycin A and calcium chelation); MHC class I expression and perforin sensitivity were equivalent, indicating the survival advantage is due to absence of a GPI-anchored NK-activating ligand(s).","method":"51Cr-release NK cytotoxicity assay, PIG-A cDNA transfection rescue, pharmacological inhibition of perforin pathway, flow cytometry","journal":"Blood","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — reciprocal comparison (mutant vs. rescued cells), multiple inhibitor controls, single lab","pmids":["12130519"],"is_preprint":false},{"year":2005,"finding":"PIGA mutant K562 cells lacking GPI-anchored proteins survive NK cell cytotoxicity due to deficiency of stress-inducible GPI-linked ULBP1 and ULBP2; antibodies to ULBPs or to NKG2D (the ULBP receptor on NK cells) made GPI-expressing cells as resistant as GPI-deficient cells, directly linking ULBP absence to the survival advantage.","method":"NK cytotoxicity assay, antibody blocking experiments, flow cytometry for ULBP expression","journal":"Blood","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — antibody rescue experiment provides mechanistic linkage, single lab","pmids":["16195329"],"is_preprint":false},{"year":2008,"finding":"PIG-A-deficient human embryonic stem cells (due to absent PIG-A expression) could form embryoid bodies and differentiate into the three germ layers but failed to form trophoblasts; the trophoblast differentiation defect was due to absence of GPI-anchored BMP co-receptors, impairing full BMP4 signaling activation.","method":"PIG-A-null hES cell clones, BMP4 differentiation assay, BMP signaling assays, flow cytometry","journal":"Cell Stem Cell","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — genetic loss-of-function with defined signaling pathway consequence, single lab, two independent hES clones","pmids":["18397754"],"is_preprint":false},{"year":2012,"finding":"A germline nonsense mutation in PIGA (p.Arg412*) results in partial (not absent) GPI-anchor biosynthesis; transfection of the mutant construct into PIGA-null cells showed partial restoration of GPI-anchored protein surface expression, establishing that this hypomorphic allele retains residual function.","method":"Transfection complementation assay in PIGA-null cells, flow cytometry for GPI-anchored protein surface expression","journal":"American Journal of Human Genetics","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — functional complementation assay in null cells, single lab","pmids":["22305531"],"is_preprint":false},{"year":2014,"finding":"Four distinct PIGA mutations causing early-onset epileptic encephalopathy showed variable loss of PIGA enzymatic activity; transient expression of PIGA mutants in PIGA-deficient JY5 cells only partially or barely restored GPI-anchored protein surface expression, and the degree of activity loss correlated with clinical severity.","method":"Transfection complementation assay in PIGA-null JY5 cells, flow cytometry for GPI-anchored protein expression on blood granulocytes and transfected cells","journal":"Neurology","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — functional complementation in null cells for multiple alleles, single lab","pmids":["24706016"],"is_preprint":false},{"year":2014,"finding":"An early frameshift mutation in PIGA (c.76dupT; p.Y26Lfs*3) produces a truncated hypomorphic protein via translation initiation at the second methionine (position 37); complementation assays confirmed that the shorter PIGA cDNA partially rescues CD59 surface expression in PIGA-null cells.","method":"Complementation assay in PIGA-null cell line, CD59 flow cytometry, molecular analysis of alternative translation initiation","journal":"Human Mutation","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — functional rescue assay in null cells, molecular characterization of alternative translation start, single lab","pmids":["24357517"],"is_preprint":false},{"year":2017,"finding":"A hypomorphic PIGA mutation (c.1234C>T) impairs neuronal differentiation in human iPSC-derived neural progenitors, with decreased proliferation, aberrant synapse formation, and abnormal membrane depolarization; neural progenitors also showed increased susceptibility to complement-mediated cytotoxicity, indicating defective complement regulation.","method":"Human iPSC model with PIGAc.1234C>T mutation, neural differentiation assays, electrophysiology, complement cytotoxicity assay","journal":"PloS One","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — iPSC disease model with multiple orthogonal functional readouts, single lab","pmids":["28441409"],"is_preprint":false},{"year":1997,"finding":"Restrictive GPI anchor synthesis in cwh6/gpi3 (yeast GPI3/PIG-A ortholog) mutant cells retards ER exit of cell wall protein precursors, causes ER proliferation, and results in secretion rather than cell wall incorporation of GPI-dependent cell wall proteins.","method":"Yeast conditional mutant analysis, subcellular fractionation, pulse-chase protein trafficking, ER morphology analysis","journal":"Journal of Bacteriology","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — genetic loss-of-function with defined ER trafficking phenotype, ortholog study in yeast","pmids":["9079905"],"is_preprint":false},{"year":1998,"finding":"PIG-A mutations do not directly confer resistance to apoptosis: stable introduction of PIG-A cDNA into GPI-negative JY5 cells (restoring GPI-anchored protein surface expression) did not alter rates of apoptosis induced by Fas antibody, serum starvation, or gamma-irradiation, indicating that the PIG-A mutation and GPI-anchor absence are not the direct cause of apoptosis resistance in PNH.","method":"Stable transfection and retroviral transduction of PIG-A cDNA into GPI-null cells, apoptosis assays (Fas, serum starvation, irradiation)","journal":"Blood","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — negative result established by functional rescue experiment with two independent introduction methods, single lab; contradicts earlier claim (PMID 9238050)","pmids":["9746796"],"is_preprint":false},{"year":2020,"finding":"Jawsamycin selectively inhibits the fungal Spt14/Gpi3 (GPI3/PIG-A ortholog) catalytic subunit of the UDP-glycosyltransferase complex at the first step of GPI biosynthesis, with good selectivity over the human PIG-A functional homolog, demonstrating that the enzymatic activity of PIG-A/Spt14 is targetable by small molecules.","method":"Reporter gene-based screen in S. cerevisiae, antifungal activity assays, target identification via genetic interaction, in vivo mouse model","journal":"Nature Communications","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — genetic and pharmacological target validation in yeast ortholog with selectivity data for human PIG-A, single study","pmids":["32636417"],"is_preprint":false}],"current_model":"PIGA encodes the catalytic subunit of the GPI-GlcNAc transferase complex, which resides in the cytoplasmic face of the ER membrane and transfers N-acetylglucosamine from UDP-GlcNAc to phosphatidylinositol as the first committed step of GPI-anchor biosynthesis; PIGA functions within a four-subunit complex (with PIG-H, PIG-C, and GPI1/hGPI1), recognizes the fatty acyl chains of PI as part of substrate selectivity, and its loss of function—whether somatic (causing PNH) or germline (causing epileptic encephalopathy/MCAHS2)—abolishes surface expression of all GPI-anchored proteins, with downstream consequences including complement hypersensitivity, NK immune evasion via ULBP loss, impaired BMP4 signaling in stem cells, and defective neuronal development."},"narrative":{"mechanistic_narrative":"PIGA encodes the catalytic subunit of the GPI-GlcNAc transferase complex that executes the first committed step of glycosylphosphatidylinositol (GPI) anchor biosynthesis—the transfer of N-acetylglucosamine from UDP-GlcNAc to phosphatidylinositol to form GlcNAc-PI [PMID:7680492, PMID:9463366]. The protein is an ER transmembrane enzyme with a large cytoplasmic domain homologous to bacterial GlcNAc transferases and a small lumenal domain required for rough-ER targeting; catalysis occurs on the cytoplasmic face of the ER membrane [PMID:8900170]. PIGA acts within a four-subunit complex with PIG-H, PIG-C, and hGPI1, which reconstitutes GPI-GnT activity in vitro and discriminates between phosphatidylinositol species by recognizing the fatty acyl chains of the substrate [PMID:8900170, PMID:9463366]. This activity is conserved and essential, as the yeast ortholog GPI3 is required for vegetative growth and GlcNAc-PI synthesis [PMID:7768896]. Loss of PIGA abolishes surface display of all GPI-anchored proteins: somatic mutation in hematopoietic cells causes paroxysmal nocturnal hemoglobinuria (PNH), with rescue by wild-type cDNA restoring GPI-linked protein expression [PMID:8306954], while hypomorphic germline alleles that retain partial enzymatic activity cause early-onset epileptic encephalopathy, with residual activity correlating with clinical severity [PMID:22305531, PMID:24706016]. The functional consequences of GPI deficiency include heightened complement-mediated lysis of affected cells [PMID:10556176, PMID:28441409], evasion of NK-cell killing through loss of the GPI-anchored NKG2D ligands ULBP1 and ULBP2 [PMID:16195329], impaired BMP4 signaling from absence of GPI-anchored co-receptors during stem-cell differentiation [PMID:18397754], and defective neuronal differentiation [PMID:28441409]. Notably, PIGA loss alone is insufficient to drive clonal expansion in PNH [PMID:9276719, PMID:10556176] and does not directly confer apoptosis resistance [PMID:9746796].","teleology":[{"year":1993,"claim":"Established that PIGA is required for the first intermediate of GPI-anchor biosynthesis, defining its position at the head of the pathway.","evidence":"cDNA cloning and functional complementation of GPI-deficient cell lines","pmids":["7680492"],"confidence":"High","gaps":["Did not resolve whether PIGA is the catalytic subunit or a cofactor","No subunit composition of the responsible enzyme"]},{"year":1994,"claim":"Identified PIGA as the causative gene of PNH by linking somatic mutations to loss of GPI-anchored proteins and rescuing the defect with wild-type cDNA.","evidence":"Transcript sequencing and complementation transfection in patient B-lymphoblastoid lines","pmids":["8306954"],"confidence":"High","gaps":["Did not explain why PIGA-mutant clones expand in PNH","Mechanism of disease phenotype beyond GPI loss unaddressed"]},{"year":1995,"claim":"Demonstrated that the enzymatic role and essentiality of PIGA are conserved through the yeast ortholog GPI3.","evidence":"Temperature-sensitive mutants, in vitro inositol incorporation, and gene disruption in S. cerevisiae","pmids":["7768896"],"confidence":"High","gaps":["Did not define the multi-subunit nature of the mammalian enzyme"]},{"year":1996,"claim":"Defined the topology of PIGA as an ER transmembrane protein catalyzing on the cytoplasmic face, with a lumenal domain for ER targeting and physical association with PIG-H.","evidence":"Co-IP, subcellular fractionation, and domain mutagenesis","pmids":["8900170"],"confidence":"High","gaps":["Full subunit composition not yet established","No structural model of the active site"]},{"year":1998,"claim":"Reconstituted the four-subunit GPI-GnT complex (PIG-A, PIG-H, PIG-C, hGPI1) and showed it recognizes PI fatty acyl chains, establishing substrate selectivity and complex boundaries.","evidence":"Co-IP, in vitro GlcNAc transferase activity, and PI species substrate assays","pmids":["9463366"],"confidence":"High","gaps":["Did not assign individual catalytic versus regulatory roles to each subunit","No atomic structure of the complex"]},{"year":1997,"claim":"Connected GPI synthesis to secretory trafficking by showing ortholog loss retards ER exit of GPI-dependent cell wall proteins.","evidence":"Yeast cwh6/gpi3 conditional mutant trafficking and ER morphology analysis","pmids":["9079905"],"confidence":"Medium","gaps":["Ortholog system; mammalian trafficking consequences not directly tested"]},{"year":1999,"claim":"Showed that Piga loss alone is insufficient to drive PNH clonal expansion, separating the enzymatic defect from clonal selection.","evidence":"Cre/loxP conditional and ES knockout mouse models with longitudinal monitoring and complement sensitivity assays","pmids":["10556176","9276719","10377440"],"confidence":"High","gaps":["The additional factor(s) required for clonal expansion remain unidentified","Tissue-specific GPI requirement mechanisms not resolved"]},{"year":2002,"claim":"Linked GPI deficiency to immune evasion, showing PIGA-mutant cells resist perforin-dependent NK killing due to loss of a GPI-anchored NK-activating ligand.","evidence":"51Cr-release NK cytotoxicity with PIGA rescue and perforin-pathway inhibitors","pmids":["12130519"],"confidence":"Medium","gaps":["Specific ligand not yet identified in this study","Single lab"]},{"year":2005,"claim":"Identified the GPI-anchored NKG2D ligands ULBP1 and ULBP2 as the missing activators responsible for NK evasion in PIGA-deficient cells.","evidence":"NK cytotoxicity with anti-ULBP and anti-NKG2D antibody blocking","pmids":["16195329"],"confidence":"Medium","gaps":["In vivo relevance to PNH clonal selection not established","Single lab"]},{"year":2008,"claim":"Showed GPI deficiency impairs developmental signaling, blocking trophoblast differentiation via loss of GPI-anchored BMP co-receptors.","evidence":"PIGA-null hES clones with BMP4 differentiation and signaling assays","pmids":["18397754"],"confidence":"Medium","gaps":["Identity of the specific GPI-anchored BMP co-receptor not defined","Single lab, two clones"]},{"year":2012,"claim":"Established a germline hypomorphic-allele paradigm by showing PIGA p.Arg412* retains partial GPI biosynthetic activity.","evidence":"Transfection complementation in PIGA-null cells with flow cytometry","pmids":["22305531"],"confidence":"Medium","gaps":["Genotype-phenotype relationship across the allelic spectrum not yet defined","Single lab"]},{"year":2014,"claim":"Demonstrated that germline PIGA hypomorphic alleles cause epileptic encephalopathy with residual activity correlating with clinical severity, and characterized alternative translation initiation rescuing function.","evidence":"Complementation assays of multiple alleles in PIGA-null JY5 cells with surface GPI-anchored protein readouts","pmids":["24706016","24357517"],"confidence":"Medium","gaps":["Mechanistic basis of neurological phenotype not directly addressed","Single lab"]},{"year":2017,"claim":"Provided cellular mechanism for the neurological disease by showing a hypomorphic PIGA mutation impairs neuronal differentiation and complement regulation in iPSC-derived neural progenitors.","evidence":"Patient-mutation iPSC neural differentiation, electrophysiology, and complement cytotoxicity assays","pmids":["28441409"],"confidence":"Medium","gaps":["Which GPI-anchored neuronal proteins mediate the defect not identified","Single lab"]},{"year":2020,"claim":"Validated the catalytic subunit as a small-molecule target by showing jawsamycin selectively inhibits the fungal GPI3/PIG-A ortholog over human PIG-A.","evidence":"Yeast reporter screen, antifungal assays, genetic target identification, and mouse model","pmids":["32636417"],"confidence":"Medium","gaps":["Human PIG-A inhibitor selectivity window not exploited therapeutically","Structural basis of selectivity unknown"]},{"year":null,"claim":"The molecular factor(s) beyond PIGA loss that confer clonal proliferative advantage in PNH, and the atomic structure of the GPI-GnT complex active site, remain undefined.","evidence":"","pmids":[],"confidence":"High","gaps":["No identified second-hit driver of PNH clonal expansion","No high-resolution structure of the four-subunit complex","Individual subunit catalytic versus regulatory roles not fully assigned"]}],"mechanism_profile":{"molecular_activity":[{"term_id":"GO:0016740","term_label":"transferase activity","supporting_discovery_ids":[0,1,2,4]}],"localization":[{"term_id":"GO:0005783","term_label":"endoplasmic reticulum","supporting_discovery_ids":[1,2]}],"pathway":[{"term_id":"R-HSA-392499","term_label":"Metabolism of proteins","supporting_discovery_ids":[0,2]}],"complexes":["GPI-GlcNAc transferase (GPI-GnT) complex"],"partners":["PIGH","PIGC","GPI1"],"other_free_text":[]}},"prefetch_data":{"uniprot":{"accession":"P37287","full_name":"Phosphatidylinositol N-acetylglucosaminyltransferase subunit A","aliases":["GlcNAc-PI synthesis protein","Phosphatidylinositol-glycan biosynthesis class A protein","PIG-A"],"length_aa":484,"mass_kda":54.1,"function":"Catalytic subunit of the glycosylphosphatidylinositol-N-acetylglucosaminyltransferase (GPI-GnT) complex that catalyzes the transfer of N-acetylglucosamine from UDP-N-acetylglucosamine to phosphatidylinositol and participates in the first step of GPI biosynthesis","subcellular_location":"Rough endoplasmic reticulum membrane","url":"https://www.uniprot.org/uniprotkb/P37287/entry"},"depmap":{"release":"DepMap","has_data":true,"is_common_essential":false,"resolved_as":"","url":"https://depmap.org/portal/gene/PIGA","classification":"Not Classified","n_dependent_lines":1,"n_total_lines":1208,"dependency_fraction":0.0008278145695364238},"opencell":{"profiled":false,"resolved_as":"","ensg_id":"","cell_line_id":"","localizations":[],"interactors":[],"url":"https://opencell.sf.czbiohub.org/search/PIGA","total_profiled":1310},"omim":[{"mim_id":"620246","title":"CONGENITAL MYOPATHY 18; CMYO18","url":"https://www.omim.org/entry/620246"},{"mim_id":"615156","title":"PROGRESSIVE EXTERNAL OPHTHALMOPLEGIA WITH MITOCHONDRIAL DNA DELETIONS, AUTOSOMAL DOMINANT 6; PEOA6","url":"https://www.omim.org/entry/615156"},{"mim_id":"614730","title":"PHOSPHATIDYLINOSITOL GLYCAN ANCHOR BIOSYNTHESIS CLASS O PROTEIN; PIGO","url":"https://www.omim.org/entry/614730"},{"mim_id":"614164","title":"GLUTATHIONE PEROXIDASE DEFICIENCY; GPXD","url":"https://www.omim.org/entry/614164"},{"mim_id":"614080","title":"MULTIPLE CONGENITAL ANOMALIES-HYPOTONIA-SEIZURES SYNDROME 1; MCAHS1","url":"https://www.omim.org/entry/614080"}],"hpa":{"profiled":true,"resolved_as":"","reliability":"","locations":[],"tissue_specificity":"Low tissue specificity","tissue_distribution":"Detected in many","driving_tissues":[],"url":"https://www.proteinatlas.org/search/PIGA"},"hgnc":{"alias_symbol":["GPI3","PIG-A"],"prev_symbol":[]},"alphafold":{"accession":"P37287","domains":[{"cath_id":"3.40.50.2000","chopping":"33-209_397-449","consensus_level":"high","plddt":89.8697,"start":33,"end":449},{"cath_id":"3.40.50.2000","chopping":"211-381","consensus_level":"high","plddt":94.6179,"start":211,"end":381}],"viewer_url":"https://alphafold.ebi.ac.uk/entry/P37287","model_url":"https://alphafold.ebi.ac.uk/files/AF-P37287-F1-model_v6.cif","pae_url":"https://alphafold.ebi.ac.uk/files/AF-P37287-F1-predicted_aligned_error_v6.png","plddt_mean":85.69},"mouse_models":{"mgi_url":"https://www.informatics.jax.org/marker/summary?nomen=PIGA","jax_strain_url":"https://www.jax.org/strain/search?query=PIGA"},"sequence":{"accession":"P37287","fasta_url":"https://rest.uniprot.org/uniprotkb/P37287.fasta","uniprot_url":"https://www.uniprot.org/uniprotkb/P37287/entry","alphafold_viewer_url":"https://alphafold.ebi.ac.uk/entry/P37287"}},"corpus_meta":[{"pmid":"7680492","id":"PMC_7680492","title":"The cloning of PIG-A, a component in the early step of GPI-anchor biosynthesis.","date":"1993","source":"Science (New York, N.Y.)","url":"https://pubmed.ncbi.nlm.nih.gov/7680492","citation_count":440,"is_preprint":false},{"pmid":"8306954","id":"PMC_8306954","title":"Paroxysmal nocturnal haemoglobinuria (PNH) is caused by somatic mutations in the PIG-A gene.","date":"1994","source":"The EMBO journal","url":"https://pubmed.ncbi.nlm.nih.gov/8306954","citation_count":329,"is_preprint":false},{"pmid":"8272086","id":"PMC_8272086","title":"Abnormalities of PIG-A transcripts in granulocytes from patients with paroxysmal nocturnal hemoglobinuria.","date":"1994","source":"The New England journal of medicine","url":"https://pubmed.ncbi.nlm.nih.gov/8272086","citation_count":212,"is_preprint":false},{"pmid":"22305531","id":"PMC_22305531","title":"The phenotype of a germline mutation in PIGA: the gene somatically mutated in paroxysmal nocturnal hemoglobinuria.","date":"2012","source":"American journal 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A Review.","date":"2021","source":"Animals : an open access journal from MDPI","url":"https://pubmed.ncbi.nlm.nih.gov/33669864","citation_count":13,"is_preprint":false},{"pmid":"29974678","id":"PMC_29974678","title":"A likely pathogenic variant putatively affecting splicing of PIGA identified in a multiple congenital anomalies hypotonia-seizures syndrome 2 (MCAHS2) family pedigree via whole-exome sequencing.","date":"2018","source":"Molecular genetics & genomic medicine","url":"https://pubmed.ncbi.nlm.nih.gov/29974678","citation_count":12,"is_preprint":false},{"pmid":"12488505","id":"PMC_12488505","title":"The effect of GPI-anchor deficiency on apoptosis in mice carrying a Piga gene mutation in hematopoietic cells.","date":"2002","source":"Journal of leukocyte biology","url":"https://pubmed.ncbi.nlm.nih.gov/12488505","citation_count":12,"is_preprint":false},{"pmid":"23896872","id":"PMC_23896872","title":"Detection of in vivo mutation in the Hprt and Pig-a genes of rat lymphocytes.","date":"2013","source":"Methods in molecular biology (Clifton, N.J.)","url":"https://pubmed.ncbi.nlm.nih.gov/23896872","citation_count":12,"is_preprint":false},{"pmid":"29098723","id":"PMC_29098723","title":"Establishing a novel Pig-a gene mutation assay in L5178YTk+/- mouse lymphoma cells.","date":"2017","source":"Environmental and molecular mutagenesis","url":"https://pubmed.ncbi.nlm.nih.gov/29098723","citation_count":11,"is_preprint":false},{"pmid":"29502866","id":"PMC_29502866","title":"A novel germline PIGA mutation causes early-onset epileptic encephalopathies in Chinese monozygotic twins.","date":"2018","source":"Brain & development","url":"https://pubmed.ncbi.nlm.nih.gov/29502866","citation_count":11,"is_preprint":false},{"pmid":"28197649","id":"PMC_28197649","title":"Dose-response relationship of temozolomide, determined by the Pig-a, comet, and micronucleus assay.","date":"2017","source":"Archives of toxicology","url":"https://pubmed.ncbi.nlm.nih.gov/28197649","citation_count":11,"is_preprint":false},{"pmid":"14578858","id":"PMC_14578858","title":"Intracellular accumulation of pIgA-R and regulators of transcytotic trafficking in cholestatic rat hepatocytes.","date":"2003","source":"Hepatology (Baltimore, Md.)","url":"https://pubmed.ncbi.nlm.nih.gov/14578858","citation_count":11,"is_preprint":false},{"pmid":"9163589","id":"PMC_9163589","title":"PIG-A gene mutations in four Taiwanese patients with paroxysmal nocturnal haemoglobinuria following aplastic anaemia.","date":"1997","source":"British journal of haematology","url":"https://pubmed.ncbi.nlm.nih.gov/9163589","citation_count":11,"is_preprint":false},{"pmid":"33925534","id":"PMC_33925534","title":"Classical, Molecular, and Genomic Cytogenetics of the Pig, a Clinical Perspective.","date":"2021","source":"Animals : an open access journal from MDPI","url":"https://pubmed.ncbi.nlm.nih.gov/33925534","citation_count":10,"is_preprint":false},{"pmid":"35033195","id":"PMC_35033195","title":"A Pig-a conditional knock-out mice model mediated by Vav-iCre: stable GPI-deficient and mild hemolysis.","date":"2022","source":"Experimental hematology & oncology","url":"https://pubmed.ncbi.nlm.nih.gov/35033195","citation_count":10,"is_preprint":false},{"pmid":"34638806","id":"PMC_34638806","title":"Rab11-FIP1 and Rab11-FIP5 Regulate pIgR/pIgA Transcytosis through TRIM21-Mediated Polyubiquitination.","date":"2021","source":"International journal of molecular sciences","url":"https://pubmed.ncbi.nlm.nih.gov/34638806","citation_count":10,"is_preprint":false},{"pmid":"27770464","id":"PMC_27770464","title":"In Vivo Pig-a gene mutation assay: Guidance for 3Rs-friendly implementation.","date":"2016","source":"Environmental and molecular mutagenesis","url":"https://pubmed.ncbi.nlm.nih.gov/27770464","citation_count":10,"is_preprint":false}],"cost":{"stage1":{"model":"claude-sonnet-4-6","input_tokens":50762,"output_tokens":4625,"usd":0.11083,"stage1_stop_reason":"end_turn"},"stage2":{"model":"claude-opus-4-8","input_tokens":12821,"output_tokens":3893,"usd":0.080715,"stage2_stop_reason":"end_turn"},"total_usd":0.191545,"stage1_batch_id":"msgbatch_01CNoDbkChHEkgrJnL7BwtGJ","stage2_batch_id":"msgbatch_016Y4x9E9Wg5VQDANj9quSQD","note":"batch pricing = 50% of standard"},"stage1_raw":"```json\n{\n  \"discoveries\": [\n    {\n      \"year\": 1993,\n      \"finding\": \"PIG-A encodes a protein necessary for the synthesis of N-acetylglucosaminyl-phosphatidylinositol (GlcNAc-PI), the first intermediate in GPI-anchor biosynthesis; complementation of GPI-anchor-deficient cells with PIG-A cDNA restored GPI-anchor synthesis.\",\n      \"method\": \"cDNA cloning, functional complementation of GPI-deficient cell lines\",\n      \"journal\": \"Science\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Strong — direct in vitro/cell-based reconstitution of enzymatic function; founding paper replicated by multiple subsequent groups\",\n      \"pmids\": [\"7680492\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1996,\n      \"finding\": \"PIG-A is an endoplasmic reticulum transmembrane protein with a large cytoplasmic domain homologous to bacterial GlcNAc transferases and a small lumenal domain; PIG-H is a cytoplasmically oriented ER-associated protein; PIG-A and PIG-H form a protein complex in the ER. The small lumenal domain of PIG-A plays an essential functional role in targeting to the rough ER. GlcNAc transfer to PI occurs on the cytoplasmic face of the ER.\",\n      \"method\": \"Co-immunoprecipitation, subcellular fractionation, domain deletion/mutagenesis, ER targeting assays\",\n      \"journal\": \"The Journal of Biological Chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1-2 / Strong — multiple orthogonal methods (Co-IP, fractionation, mutagenesis) in a single focused study, subsequently confirmed by the 1998 complex paper\",\n      \"pmids\": [\"8900170\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1998,\n      \"finding\": \"The first step of GPI biosynthesis (transfer of GlcNAc from UDP-GlcNAc to PI) is catalyzed by a complex of four mammalian proteins—PIG-A, PIG-H, PIG-C, and hGPI1—resident in the ER membrane. The reconstituted complex had GPI-GlcNAc transferase (GPI-GnT) activity in vitro but did not catalyze the second reaction. Bovine PI was utilized ~100-fold more efficiently than soybean PI, indicating that the complex recognizes fatty acyl chains of PI. PIG-L (involved in step 2) did not associate with the isolated complex.\",\n      \"method\": \"Co-immunoprecipitation, in vitro GlcNAc transferase activity assay, substrate specificity assay with different PI species\",\n      \"journal\": \"The EMBO Journal\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Strong — in vitro enzymatic reconstitution plus Co-IP complex identification, multiple orthogonal approaches in one study\",\n      \"pmids\": [\"9463366\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1994,\n      \"finding\": \"Somatic mutations in PIG-A (frameshift, missense, nonsense, splice site) in hematopoietic cells cause paroxysmal nocturnal hemoglobinuria (PNH); transfection of wild-type PIG-A cDNA into EBV-transformed B-lymphoblastoid cell lines from PNH patients fully restored GPI-linked protein surface expression, proving PIG-A is the causative gene.\",\n      \"method\": \"RT-PCR/sequencing of PIG-A transcripts, functional complementation transfection assay, flow cytometry\",\n      \"journal\": \"The EMBO Journal\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — functional rescue by cDNA complementation plus mutation identification, replicated across multiple independent patient cell lines and subsequent studies\",\n      \"pmids\": [\"8306954\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1995,\n      \"finding\": \"The yeast GPI3 gene (ortholog of mammalian PIG-A) encodes a protein required for GlcNAc-PI synthesis (first step of GPI anchor biosynthesis); gpi3 mutants lack in vitro GlcNAc-PI synthetic activity; GPI3 is essential for vegetative growth in yeast.\",\n      \"method\": \"Temperature-sensitive mutant isolation, in vitro [3H]-inositol incorporation assay, gene disruption, genetic complementation\",\n      \"journal\": \"The Journal of Biological Chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Strong — in vitro enzymatic assay plus genetic complementation and gene disruption in yeast ortholog\",\n      \"pmids\": [\"7768896\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1997,\n      \"finding\": \"Pig-a gene inactivation in mouse embryonic stem cells by homologous recombination produced cells competent for hematopoiesis with the PNH phenotype, but pig-a inactivation alone did not confer a proliferative advantage to hematopoietic stem cells, demonstrating that additional factors are required for PNH clone expansion.\",\n      \"method\": \"Homologous recombination (gene knockout) in murine ES cells, chimera generation, flow cytometry\",\n      \"journal\": \"The Journal of Clinical Investigation\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — clean genetic knockout with defined cellular phenotype readout, replicated in multiple subsequent mouse models\",\n      \"pmids\": [\"9276719\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1999,\n      \"finding\": \"Cre/loxP-mediated inactivation of Piga in mosaic mice showed that PIGA(-) blood cells are more sensitive to complement-mediated lysis and have a decreased lifespan in circulation, but the PIGA(-) cell population did not expand over 12 months, confirming that Piga mutation alone is insufficient to cause PNH.\",\n      \"method\": \"Cre/loxP conditional knockout, flow cytometry, complement sensitivity assay, longitudinal monitoring\",\n      \"journal\": \"Blood\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — conditional genetic model with multiple functional readouts (complement lysis, lifespan), 12-month longitudinal follow-up\",\n      \"pmids\": [\"10556176\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1999,\n      \"finding\": \"X chromosome inactivation and somatic cell selection rescue female mice carrying a Piga-null mutation. Tissue analysis showed that most somatic tissues (heart, lung, kidney, brain, liver) preferentially express wild-type Piga, suggesting these tissues require GPI-linked proteins, whereas spleen, thymus, and red blood cells had roughly equal proportions of Piga(+) and Piga(-) cells.\",\n      \"method\": \"Cre/loxP conditional knockout (EIIa-Cre), tissue fractionation, flow cytometry, X-inactivation analysis\",\n      \"journal\": \"Proceedings of the National Academy of Sciences\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — conditional knockout with tissue-level functional consequence, multiple tissues analyzed\",\n      \"pmids\": [\"10377440\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2001,\n      \"finding\": \"GATA1-Cre-mediated Piga inactivation restricted to the erythroid/megakaryocytic lineage produced mice with up to 100% GPI-deficient red cells; the loss of GPI-linked proteins occurred late in erythroid differentiation, resulting in residual low-level GPI expression resembling PNH type II cells, which showed intermediate complement sensitivity. Recombination was also detected in megakaryocytes, mast cells, and eosinophils but not in neutrophils, lymphocytes, or non-hematopoietic tissues.\",\n      \"method\": \"GATA1-Cre/loxP conditional knockout, flow cytometry, complement sensitivity assay\",\n      \"journal\": \"Blood\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — lineage-specific conditional knockout with defined complement-sensitivity phenotype and cell-type specificity mapping\",\n      \"pmids\": [\"11568013\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2002,\n      \"finding\": \"PIG-A mutant leukemic cells lacking GPI-anchored proteins showed decreased susceptibility to natural killer (NK) cell killing compared to PIG-A-rescued controls; killing was perforin-dependent (abolished by concanamycin A and calcium chelation); MHC class I expression and perforin sensitivity were equivalent, indicating the survival advantage is due to absence of a GPI-anchored NK-activating ligand(s).\",\n      \"method\": \"51Cr-release NK cytotoxicity assay, PIG-A cDNA transfection rescue, pharmacological inhibition of perforin pathway, flow cytometry\",\n      \"journal\": \"Blood\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — reciprocal comparison (mutant vs. rescued cells), multiple inhibitor controls, single lab\",\n      \"pmids\": [\"12130519\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2005,\n      \"finding\": \"PIGA mutant K562 cells lacking GPI-anchored proteins survive NK cell cytotoxicity due to deficiency of stress-inducible GPI-linked ULBP1 and ULBP2; antibodies to ULBPs or to NKG2D (the ULBP receptor on NK cells) made GPI-expressing cells as resistant as GPI-deficient cells, directly linking ULBP absence to the survival advantage.\",\n      \"method\": \"NK cytotoxicity assay, antibody blocking experiments, flow cytometry for ULBP expression\",\n      \"journal\": \"Blood\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — antibody rescue experiment provides mechanistic linkage, single lab\",\n      \"pmids\": [\"16195329\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2008,\n      \"finding\": \"PIG-A-deficient human embryonic stem cells (due to absent PIG-A expression) could form embryoid bodies and differentiate into the three germ layers but failed to form trophoblasts; the trophoblast differentiation defect was due to absence of GPI-anchored BMP co-receptors, impairing full BMP4 signaling activation.\",\n      \"method\": \"PIG-A-null hES cell clones, BMP4 differentiation assay, BMP signaling assays, flow cytometry\",\n      \"journal\": \"Cell Stem Cell\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — genetic loss-of-function with defined signaling pathway consequence, single lab, two independent hES clones\",\n      \"pmids\": [\"18397754\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2012,\n      \"finding\": \"A germline nonsense mutation in PIGA (p.Arg412*) results in partial (not absent) GPI-anchor biosynthesis; transfection of the mutant construct into PIGA-null cells showed partial restoration of GPI-anchored protein surface expression, establishing that this hypomorphic allele retains residual function.\",\n      \"method\": \"Transfection complementation assay in PIGA-null cells, flow cytometry for GPI-anchored protein surface expression\",\n      \"journal\": \"American Journal of Human Genetics\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — functional complementation assay in null cells, single lab\",\n      \"pmids\": [\"22305531\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2014,\n      \"finding\": \"Four distinct PIGA mutations causing early-onset epileptic encephalopathy showed variable loss of PIGA enzymatic activity; transient expression of PIGA mutants in PIGA-deficient JY5 cells only partially or barely restored GPI-anchored protein surface expression, and the degree of activity loss correlated with clinical severity.\",\n      \"method\": \"Transfection complementation assay in PIGA-null JY5 cells, flow cytometry for GPI-anchored protein expression on blood granulocytes and transfected cells\",\n      \"journal\": \"Neurology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — functional complementation in null cells for multiple alleles, single lab\",\n      \"pmids\": [\"24706016\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2014,\n      \"finding\": \"An early frameshift mutation in PIGA (c.76dupT; p.Y26Lfs*3) produces a truncated hypomorphic protein via translation initiation at the second methionine (position 37); complementation assays confirmed that the shorter PIGA cDNA partially rescues CD59 surface expression in PIGA-null cells.\",\n      \"method\": \"Complementation assay in PIGA-null cell line, CD59 flow cytometry, molecular analysis of alternative translation initiation\",\n      \"journal\": \"Human Mutation\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — functional rescue assay in null cells, molecular characterization of alternative translation start, single lab\",\n      \"pmids\": [\"24357517\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2017,\n      \"finding\": \"A hypomorphic PIGA mutation (c.1234C>T) impairs neuronal differentiation in human iPSC-derived neural progenitors, with decreased proliferation, aberrant synapse formation, and abnormal membrane depolarization; neural progenitors also showed increased susceptibility to complement-mediated cytotoxicity, indicating defective complement regulation.\",\n      \"method\": \"Human iPSC model with PIGAc.1234C>T mutation, neural differentiation assays, electrophysiology, complement cytotoxicity assay\",\n      \"journal\": \"PloS One\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — iPSC disease model with multiple orthogonal functional readouts, single lab\",\n      \"pmids\": [\"28441409\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1997,\n      \"finding\": \"Restrictive GPI anchor synthesis in cwh6/gpi3 (yeast GPI3/PIG-A ortholog) mutant cells retards ER exit of cell wall protein precursors, causes ER proliferation, and results in secretion rather than cell wall incorporation of GPI-dependent cell wall proteins.\",\n      \"method\": \"Yeast conditional mutant analysis, subcellular fractionation, pulse-chase protein trafficking, ER morphology analysis\",\n      \"journal\": \"Journal of Bacteriology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — genetic loss-of-function with defined ER trafficking phenotype, ortholog study in yeast\",\n      \"pmids\": [\"9079905\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1998,\n      \"finding\": \"PIG-A mutations do not directly confer resistance to apoptosis: stable introduction of PIG-A cDNA into GPI-negative JY5 cells (restoring GPI-anchored protein surface expression) did not alter rates of apoptosis induced by Fas antibody, serum starvation, or gamma-irradiation, indicating that the PIG-A mutation and GPI-anchor absence are not the direct cause of apoptosis resistance in PNH.\",\n      \"method\": \"Stable transfection and retroviral transduction of PIG-A cDNA into GPI-null cells, apoptosis assays (Fas, serum starvation, irradiation)\",\n      \"journal\": \"Blood\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — negative result established by functional rescue experiment with two independent introduction methods, single lab; contradicts earlier claim (PMID 9238050)\",\n      \"pmids\": [\"9746796\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2020,\n      \"finding\": \"Jawsamycin selectively inhibits the fungal Spt14/Gpi3 (GPI3/PIG-A ortholog) catalytic subunit of the UDP-glycosyltransferase complex at the first step of GPI biosynthesis, with good selectivity over the human PIG-A functional homolog, demonstrating that the enzymatic activity of PIG-A/Spt14 is targetable by small molecules.\",\n      \"method\": \"Reporter gene-based screen in S. cerevisiae, antifungal activity assays, target identification via genetic interaction, in vivo mouse model\",\n      \"journal\": \"Nature Communications\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — genetic and pharmacological target validation in yeast ortholog with selectivity data for human PIG-A, single study\",\n      \"pmids\": [\"32636417\"],\n      \"is_preprint\": false\n    }\n  ],\n  \"current_model\": \"PIGA encodes the catalytic subunit of the GPI-GlcNAc transferase complex, which resides in the cytoplasmic face of the ER membrane and transfers N-acetylglucosamine from UDP-GlcNAc to phosphatidylinositol as the first committed step of GPI-anchor biosynthesis; PIGA functions within a four-subunit complex (with PIG-H, PIG-C, and GPI1/hGPI1), recognizes the fatty acyl chains of PI as part of substrate selectivity, and its loss of function—whether somatic (causing PNH) or germline (causing epileptic encephalopathy/MCAHS2)—abolishes surface expression of all GPI-anchored proteins, with downstream consequences including complement hypersensitivity, NK immune evasion via ULBP loss, impaired BMP4 signaling in stem cells, and defective neuronal development.\"\n}\n```","stage2_raw":"{\n  \"mechanistic_narrative\": \"PIGA encodes the catalytic subunit of the GPI-GlcNAc transferase complex that executes the first committed step of glycosylphosphatidylinositol (GPI) anchor biosynthesis—the transfer of N-acetylglucosamine from UDP-GlcNAc to phosphatidylinositol to form GlcNAc-PI [#0, #2]. The protein is an ER transmembrane enzyme with a large cytoplasmic domain homologous to bacterial GlcNAc transferases and a small lumenal domain required for rough-ER targeting; catalysis occurs on the cytoplasmic face of the ER membrane [#1]. PIGA acts within a four-subunit complex with PIG-H, PIG-C, and hGPI1, which reconstitutes GPI-GnT activity in vitro and discriminates between phosphatidylinositol species by recognizing the fatty acyl chains of the substrate [#1, #2]. This activity is conserved and essential, as the yeast ortholog GPI3 is required for vegetative growth and GlcNAc-PI synthesis [#4]. Loss of PIGA abolishes surface display of all GPI-anchored proteins: somatic mutation in hematopoietic cells causes paroxysmal nocturnal hemoglobinuria (PNH), with rescue by wild-type cDNA restoring GPI-linked protein expression [#3], while hypomorphic germline alleles that retain partial enzymatic activity cause early-onset epileptic encephalopathy, with residual activity correlating with clinical severity [#12, #13]. The functional consequences of GPI deficiency include heightened complement-mediated lysis of affected cells [#6, #15], evasion of NK-cell killing through loss of the GPI-anchored NKG2D ligands ULBP1 and ULBP2 [#10], impaired BMP4 signaling from absence of GPI-anchored co-receptors during stem-cell differentiation [#11], and defective neuronal differentiation [#15]. Notably, PIGA loss alone is insufficient to drive clonal expansion in PNH [#5, #6] and does not directly confer apoptosis resistance [#17].\",\n  \"teleology\": [\n    {\n      \"year\": 1993,\n      \"claim\": \"Established that PIGA is required for the first intermediate of GPI-anchor biosynthesis, defining its position at the head of the pathway.\",\n      \"evidence\": \"cDNA cloning and functional complementation of GPI-deficient cell lines\",\n      \"pmids\": [\"7680492\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Did not resolve whether PIGA is the catalytic subunit or a cofactor\", \"No subunit composition of the responsible enzyme\"]\n    },\n    {\n      \"year\": 1994,\n      \"claim\": \"Identified PIGA as the causative gene of PNH by linking somatic mutations to loss of GPI-anchored proteins and rescuing the defect with wild-type cDNA.\",\n      \"evidence\": \"Transcript sequencing and complementation transfection in patient B-lymphoblastoid lines\",\n      \"pmids\": [\"8306954\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Did not explain why PIGA-mutant clones expand in PNH\", \"Mechanism of disease phenotype beyond GPI loss unaddressed\"]\n    },\n    {\n      \"year\": 1995,\n      \"claim\": \"Demonstrated that the enzymatic role and essentiality of PIGA are conserved through the yeast ortholog GPI3.\",\n      \"evidence\": \"Temperature-sensitive mutants, in vitro inositol incorporation, and gene disruption in S. cerevisiae\",\n      \"pmids\": [\"7768896\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Did not define the multi-subunit nature of the mammalian enzyme\"]\n    },\n    {\n      \"year\": 1996,\n      \"claim\": \"Defined the topology of PIGA as an ER transmembrane protein catalyzing on the cytoplasmic face, with a lumenal domain for ER targeting and physical association with PIG-H.\",\n      \"evidence\": \"Co-IP, subcellular fractionation, and domain mutagenesis\",\n      \"pmids\": [\"8900170\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Full subunit composition not yet established\", \"No structural model of the active site\"]\n    },\n    {\n      \"year\": 1998,\n      \"claim\": \"Reconstituted the four-subunit GPI-GnT complex (PIG-A, PIG-H, PIG-C, hGPI1) and showed it recognizes PI fatty acyl chains, establishing substrate selectivity and complex boundaries.\",\n      \"evidence\": \"Co-IP, in vitro GlcNAc transferase activity, and PI species substrate assays\",\n      \"pmids\": [\"9463366\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Did not assign individual catalytic versus regulatory roles to each subunit\", \"No atomic structure of the complex\"]\n    },\n    {\n      \"year\": 1997,\n      \"claim\": \"Connected GPI synthesis to secretory trafficking by showing ortholog loss retards ER exit of GPI-dependent cell wall proteins.\",\n      \"evidence\": \"Yeast cwh6/gpi3 conditional mutant trafficking and ER morphology analysis\",\n      \"pmids\": [\"9079905\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Ortholog system; mammalian trafficking consequences not directly tested\"]\n    },\n    {\n      \"year\": 1999,\n      \"claim\": \"Showed that Piga loss alone is insufficient to drive PNH clonal expansion, separating the enzymatic defect from clonal selection.\",\n      \"evidence\": \"Cre/loxP conditional and ES knockout mouse models with longitudinal monitoring and complement sensitivity assays\",\n      \"pmids\": [\"10556176\", \"9276719\", \"10377440\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"The additional factor(s) required for clonal expansion remain unidentified\", \"Tissue-specific GPI requirement mechanisms not resolved\"]\n    },\n    {\n      \"year\": 2002,\n      \"claim\": \"Linked GPI deficiency to immune evasion, showing PIGA-mutant cells resist perforin-dependent NK killing due to loss of a GPI-anchored NK-activating ligand.\",\n      \"evidence\": \"51Cr-release NK cytotoxicity with PIGA rescue and perforin-pathway inhibitors\",\n      \"pmids\": [\"12130519\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Specific ligand not yet identified in this study\", \"Single lab\"]\n    },\n    {\n      \"year\": 2005,\n      \"claim\": \"Identified the GPI-anchored NKG2D ligands ULBP1 and ULBP2 as the missing activators responsible for NK evasion in PIGA-deficient cells.\",\n      \"evidence\": \"NK cytotoxicity with anti-ULBP and anti-NKG2D antibody blocking\",\n      \"pmids\": [\"16195329\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"In vivo relevance to PNH clonal selection not established\", \"Single lab\"]\n    },\n    {\n      \"year\": 2008,\n      \"claim\": \"Showed GPI deficiency impairs developmental signaling, blocking trophoblast differentiation via loss of GPI-anchored BMP co-receptors.\",\n      \"evidence\": \"PIGA-null hES clones with BMP4 differentiation and signaling assays\",\n      \"pmids\": [\"18397754\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Identity of the specific GPI-anchored BMP co-receptor not defined\", \"Single lab, two clones\"]\n    },\n    {\n      \"year\": 2012,\n      \"claim\": \"Established a germline hypomorphic-allele paradigm by showing PIGA p.Arg412* retains partial GPI biosynthetic activity.\",\n      \"evidence\": \"Transfection complementation in PIGA-null cells with flow cytometry\",\n      \"pmids\": [\"22305531\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Genotype-phenotype relationship across the allelic spectrum not yet defined\", \"Single lab\"]\n    },\n    {\n      \"year\": 2014,\n      \"claim\": \"Demonstrated that germline PIGA hypomorphic alleles cause epileptic encephalopathy with residual activity correlating with clinical severity, and characterized alternative translation initiation rescuing function.\",\n      \"evidence\": \"Complementation assays of multiple alleles in PIGA-null JY5 cells with surface GPI-anchored protein readouts\",\n      \"pmids\": [\"24706016\", \"24357517\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Mechanistic basis of neurological phenotype not directly addressed\", \"Single lab\"]\n    },\n    {\n      \"year\": 2017,\n      \"claim\": \"Provided cellular mechanism for the neurological disease by showing a hypomorphic PIGA mutation impairs neuronal differentiation and complement regulation in iPSC-derived neural progenitors.\",\n      \"evidence\": \"Patient-mutation iPSC neural differentiation, electrophysiology, and complement cytotoxicity assays\",\n      \"pmids\": [\"28441409\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Which GPI-anchored neuronal proteins mediate the defect not identified\", \"Single lab\"]\n    },\n    {\n      \"year\": 2020,\n      \"claim\": \"Validated the catalytic subunit as a small-molecule target by showing jawsamycin selectively inhibits the fungal GPI3/PIG-A ortholog over human PIG-A.\",\n      \"evidence\": \"Yeast reporter screen, antifungal assays, genetic target identification, and mouse model\",\n      \"pmids\": [\"32636417\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Human PIG-A inhibitor selectivity window not exploited therapeutically\", \"Structural basis of selectivity unknown\"]\n    },\n    {\n      \"year\": null,\n      \"claim\": \"The molecular factor(s) beyond PIGA loss that confer clonal proliferative advantage in PNH, and the atomic structure of the GPI-GnT complex active site, remain undefined.\",\n      \"evidence\": \"\",\n      \"pmids\": [],\n      \"confidence\": \"High\",\n      \"gaps\": [\"No identified second-hit driver of PNH clonal expansion\", \"No high-resolution structure of the four-subunit complex\", \"Individual subunit catalytic versus regulatory roles not fully assigned\"]\n    }\n  ],\n  \"mechanism_profile\": {\n    \"molecular_activity\": [\n      {\"term_id\": \"GO:0016740\", \"supporting_discovery_ids\": [0, 1, 2, 4]},\n      {\"term_id\": \"GO:0016757\", \"supporting_discovery_ids\": [0, 2]}\n    ],\n    \"localization\": [\n      {\"term_id\": \"GO:0005783\", \"supporting_discovery_ids\": [1, 2]}\n    ],\n    \"pathway\": [\n      {\"term_id\": \"R-HSA-392499\", \"supporting_discovery_ids\": [0, 2]}\n    ],\n    \"complexes\": [\"GPI-GlcNAc transferase (GPI-GnT) complex\"],\n    \"partners\": [\"PIGH\", \"PIGC\", \"GPI1\"],\n    \"other_free_text\": []\n  }\n}","audit_flag":null,"evaluation":{"pairwise":"win","faith_supported":7,"faith_total":7,"faith_pct":100.0}}