{"gene":"KDSR","run_date":"2026-06-10T02:59:49","timeline":{"discoveries":[{"year":2004,"finding":"Human FVT-1 (KDSR) functions as a 3-ketodihydrosphingosine (KDS) reductase: recombinant hFVT-1 exhibits NADPH-dependent KDS reductase activity in vitro, and forced expression in TSC10-null yeast suppresses growth defects, establishing it as the mammalian KDS reductase.","method":"In vitro enzyme assay with purified recombinant protein, yeast complementation (TSC10-null rescue), overexpression in cultured cells","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 1 / Strong — purified recombinant protein in vitro assay with NADPH dependence, plus yeast complementation as orthogonal functional validation, both in the same study","pmids":["15328338"],"is_preprint":false},{"year":2004,"finding":"hFVT-1 (KDSR) localizes to the endoplasmic reticulum, and the large hydrophilic domain containing putative active-site residues faces the cytosolic side of the ER membrane, indicating that KDS is reduced to dihydrosphingosine on the cytosolic face of the ER.","method":"Immunofluorescence microscopy (ER colocalization) and proteinase K digestion topology assay","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 2 / Strong — two orthogonal methods (immunofluorescence + protease protection assay) in one rigorous study establishing ER localization and active-site topology","pmids":["15328338"],"is_preprint":false},{"year":2009,"finding":"FVT1 (KDSR) is the principal 3-ketosphinganine reductase in mammalian cells: siRNA silencing of FVT1 directly reduced cellular reductase activity in proportion to FVT1 levels. The N-terminal membrane-spanning domain of FVT1 (absent in yeast Tsc10p) targets it to the ER lumen and confers distinct topology relative to yeast Tsc10p. Mutation of conserved catalytic residues differentially affected FVT1 vs. Tsc10p activity, revealing mechanistic differences between the two orthologs.","method":"siRNA knockdown with enzymatic activity measurement; N-terminal GFP fusion for ER-targeting domain mapping; factor Xa protease domain removal; active-site mutagenesis","journal":"Journal of lipid research","confidence":"High","confidence_rationale":"Tier 1–2 / Strong — multiple orthogonal methods (knockdown + activity assay, GFP fusion targeting, protease digestion, mutagenesis) in one study establishing principal reductase role and mechanistic details","pmids":["19141869"],"is_preprint":false},{"year":2007,"finding":"A missense mutation (Ala-175→Thr) in bovine FVT1 (KDSR) abolishes 3-ketodihydrosphingosine reductase activity in vitro, yet the mutant protein retains sufficient residual in vivo activity to complement a yeast knockout, explaining why SMA-affected calves are viable but develop neuron-specific degeneration.","method":"In vitro enzyme assay comparing Ala-175 vs. Thr-175 variants; yeast complementation assay","journal":"Proceedings of the National Academy of Sciences of the United States of America","confidence":"High","confidence_rationale":"Tier 1 / Moderate — in vitro enzymatic activity assay with defined mutation plus orthogonal yeast complementation, single lab but rigorous biochemical controls","pmids":["17420465"],"is_preprint":false},{"year":2017,"finding":"Loss-of-function mutations in KDSR reduce ceramide levels in skin and impair KDSR enzymatic activity, causing defective acylceramide synthesis and leading to skin hyperkeratosis; thrombocytopenia is also present, indicating KDSR activity is required for normal platelet function.","method":"Whole-exome sequencing identifying mutations; KDSR enzymatic activity measurement in patient samples; ceramide level quantification in skin","journal":"The Journal of investigative dermatology","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — enzymatic activity measured in patient-derived material, ceramide metabolite profiling, but no reconstitution experiment; single lab","pmids":["28774589"],"is_preprint":false},{"year":2017,"finding":"KDSR mutations causing exon skipping (including a recurrent silent third-base change) disrupt KDSR function as demonstrated by yeast complementation failure, establishing that loss of KDSR enzymatic activity underlies progressive symmetric erythrokeratoderma.","method":"Splicing assay (cDNA sequencing), yeast complementation, immunohistochemistry","journal":"American journal of human genetics","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — yeast complementation as functional readout plus splicing assay; multiple orthogonal approaches in one study but patient-based rather than reconstituted","pmids":["28575652"],"is_preprint":false},{"year":2018,"finding":"KDSR insufficiency impairs proplatelet formation from megakaryocytes: CD34+-derived megakaryocytes from KDSR-deficient patients showed hyperproliferation and reduced proplatelet formation, reversed by re-expression of functional KDSR in iPSC-derived megakaryocytes. Kdsr depletion in zebrafish recapitulated thrombocytopenia. A compensatory in vivo pathway partially normalizes downstream ceramide levels.","method":"CD34+ stem cell-derived megakaryocyte culture, iPSC differentiation with KDSR rescue, zebrafish kdsr morpholino knockdown, broad metabolomics screen","journal":"Haematologica","confidence":"High","confidence_rationale":"Tier 2 / Strong — rescue experiment (iPSC + functional KDSR re-expression), zebrafish model replication, metabolomics; multiple orthogonal methods across human and animal models","pmids":["30467204"],"is_preprint":false},{"year":2022,"finding":"In patients with biallelic KDSR mutations, the KDSR substrate 3-ketodihydrosphingosine accumulates and is processed by ceramide synthases to produce novel keto-type ceramides (up to 10% of ceramide species) in the stratum corneum, revealing a bypass pathway when KDSR is non-functional and demonstrating that tight intermediate regulation during sphingolipid anabolism is required for normal ceramide composition.","method":"Stratum corneum lipid analysis by mass spectrometry in KDSR-mutant patients vs. controls; structural identification of keto-type ceramides","journal":"Human molecular genetics","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — novel lipid species identified by mass spectrometry in patient tissue; mechanistically informative but patient-based, not reconstituted biochemistry","pmids":["34686882"],"is_preprint":false}],"current_model":"KDSR (FVT1) encodes an NADPH-dependent 3-ketodihydrosphingosine reductase that is an integral endoplasmic reticulum membrane protein with its catalytic domain facing the cytosol; it is the principal enzyme catalyzing the second step of de novo ceramide/sphingolipid biosynthesis (conversion of 3-ketodihydrosphingosine to dihydrosphingosine/sphinganine), and its loss of function—through missense, splice, or frameshift mutations—disrupts ceramide production, causes accumulation of novel keto-type ceramide species, and leads to keratinization disorders, while also impairing megakaryocyte proplatelet formation and resulting in thrombocytopenia."},"narrative":{"mechanistic_narrative":"KDSR (FVT1) is the principal mammalian NADPH-dependent 3-ketodihydrosphingosine reductase, catalyzing the second step of de novo sphingolipid biosynthesis by reducing 3-ketodihydrosphingosine to dihydrosphingosine [PMID:15328338, PMID:19141869]. It is an integral endoplasmic reticulum membrane protein in which an N-terminal membrane-spanning domain anchors a large hydrophilic catalytic domain on the cytosolic face of the ER, defining where this reduction occurs [PMID:15328338, PMID:19141869]. Loss-of-function mutations abolish or reduce reductase activity and lower ceramide levels in skin, causing defective acylceramide synthesis and keratinization disorders including progressive symmetric erythrokeratoderma [PMID:28774589, PMID:28575652]; KDSR deficiency also impairs proplatelet formation from megakaryocytes, with patient megakaryocytes showing hyperproliferation and reduced proplatelet output that is rescued by re-expression of functional KDSR, and is accompanied by thrombocytopenia [PMID:30467204]. When KDSR is non-functional, its accumulated substrate is shunted through ceramide synthases to generate novel keto-type ceramide species in the stratum corneum, revealing a bypass pathway that partially compensates downstream lipid levels [PMID:30467204, PMID:34686882].","teleology":[{"year":2004,"claim":"Established the molecular identity and enzymatic activity of human FVT1/KDSR, answering whether it served as the mammalian counterpart to yeast Tsc10p in sphingolipid synthesis.","evidence":"In vitro NADPH-dependent reductase assay with recombinant protein and TSC10-null yeast complementation","pmids":["15328338"],"confidence":"High","gaps":["Did not establish in vivo contribution relative to other reductases","No structural model of the catalytic site"]},{"year":2004,"claim":"Defined the subcellular localization and membrane topology, showing the reaction occurs on the cytosolic face of the ER.","evidence":"Immunofluorescence ER colocalization and proteinase K protection topology assay","pmids":["15328338"],"confidence":"High","gaps":["Topology assignment refined in later work (lumenal vs cytosolic active-site orientation)","Membrane insertion mechanism not addressed"]},{"year":2007,"claim":"Linked a specific missense substitution to disease by showing it abolishes in vitro activity while retaining residual in vivo function, explaining a tissue-restricted degenerative phenotype.","evidence":"In vitro activity comparison of bovine Ala-175 vs Thr-175 variants and yeast complementation","pmids":["17420465"],"confidence":"High","gaps":["Mechanism of neuron-specific vulnerability not resolved","Human relevance of bovine variant not directly tested"]},{"year":2009,"claim":"Demonstrated KDSR is the principal cellular 3-ketosphinganine reductase and mapped the N-terminal ER-targeting domain, clarifying mechanistic divergence from yeast Tsc10p.","evidence":"siRNA knockdown with activity measurement, GFP-fusion targeting, protease domain removal, and catalytic-residue mutagenesis","pmids":["19141869"],"confidence":"High","gaps":["Functional consequence of distinct topology not fully defined","No structural basis for catalytic-residue differences"]},{"year":2017,"claim":"Connected biallelic KDSR loss of function to human keratinization disease through reduced enzymatic activity, lowered skin ceramide, and concurrent thrombocytopenia.","evidence":"Whole-exome sequencing, patient-sample reductase activity, skin ceramide quantification, and splicing/yeast complementation assays","pmids":["28774589","28575652"],"confidence":"Medium","gaps":["No reconstitution of mutant enzymes in defined system","Genotype-phenotype severity relationship incompletely mapped"]},{"year":2018,"claim":"Established a cell-autonomous role for KDSR in megakaryocyte proplatelet formation and validated causality through rescue and an animal model.","evidence":"Patient CD34+/iPSC-derived megakaryocyte culture with functional KDSR re-expression, zebrafish kdsr morpholino knockdown, and metabolomics","pmids":["30467204"],"confidence":"High","gaps":["Identity of the compensatory in vivo pathway not defined","Molecular link between ceramide deficit and proplatelet defect unresolved"]},{"year":2022,"claim":"Revealed a substrate-shunting bypass in which accumulated 3-ketodihydrosphingosine is converted into novel keto-type ceramides, explaining altered skin ceramide composition under KDSR loss.","evidence":"Mass spectrometry lipidomics and structural identification of keto-ceramides in patient stratum corneum","pmids":["34686882"],"confidence":"Medium","gaps":["Enzymes responsible for keto-ceramide production not directly identified","Functional impact of keto-ceramides on skin barrier not established"]},{"year":null,"claim":"The structural basis of catalysis and the molecular mechanism linking ceramide deficiency to tissue-specific phenotypes (skin, platelets, neurons) remain unresolved.","evidence":"","pmids":[],"confidence":"Medium","gaps":["No high-resolution structure of human KDSR","Compensatory bypass pathway and its regulators uncharacterized","Mechanistic basis for tissue selectivity of phenotypes unknown"]}],"mechanism_profile":{"molecular_activity":[{"term_id":"GO:0016491","term_label":"oxidoreductase activity","supporting_discovery_ids":[0,2,3]}],"localization":[{"term_id":"GO:0005783","term_label":"endoplasmic reticulum","supporting_discovery_ids":[1,2]}],"pathway":[{"term_id":"R-HSA-1430728","term_label":"Metabolism","supporting_discovery_ids":[0,4,7]}],"complexes":[],"partners":[],"other_free_text":[]}},"prefetch_data":{"uniprot":{"accession":"Q06136","full_name":"3-ketodihydrosphingosine reductase","aliases":["3-dehydrosphinganine reductase","Follicular variant translocation protein 1","FVT-1","Short chain dehydrogenase/reductase family 35C member 1"],"length_aa":332,"mass_kda":36.2,"function":"Catalyzes the reduction of 3'-oxosphinganine (3-ketodihydrosphingosine/KDS) to sphinganine (dihydrosphingosine/DHS), the second step of de novo sphingolipid biosynthesis","subcellular_location":"Endoplasmic reticulum membrane","url":"https://www.uniprot.org/uniprotkb/Q06136/entry"},"depmap":{"release":"DepMap","has_data":true,"is_common_essential":false,"resolved_as":"","url":"https://depmap.org/portal/gene/KDSR","classification":"Not Classified","n_dependent_lines":287,"n_total_lines":1208,"dependency_fraction":0.23758278145695363},"opencell":{"profiled":true,"resolved_as":"","ensg_id":"ENSG00000119537","cell_line_id":"CID000294","localizations":[{"compartment":"er","grade":3},{"compartment":"vesicles","grade":3}],"interactors":[{"gene":"COPB2","stoichiometry":0.2},{"gene":"ARAF","stoichiometry":0.2},{"gene":"PGAM1","stoichiometry":0.2}],"url":"https://opencell.sf.czbiohub.org/target/CID000294","total_profiled":1310},"omim":[{"mim_id":"617526","title":"ERYTHROKERATODERMIA VARIABILIS ET PROGRESSIVA 4; EKVP4","url":"https://www.omim.org/entry/617526"},{"mim_id":"136440","title":"3-@KETODIHYDROSPHINGOSINE REDUCTASE; KDSR","url":"https://www.omim.org/entry/136440"},{"mim_id":"133200","title":"ERYTHROKERATODERMIA VARIABILIS ET PROGRESSIVA 1; EKVP1","url":"https://www.omim.org/entry/133200"}],"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/KDSR"},"hgnc":{"alias_symbol":["DHSR","SDR35C1"],"prev_symbol":["FVT1"]},"alphafold":{"accession":"Q06136","domains":[{"cath_id":"3.40.50.720","chopping":"28-296","consensus_level":"medium","plddt":96.7512,"start":28,"end":296}],"viewer_url":"https://alphafold.ebi.ac.uk/entry/Q06136","model_url":"https://alphafold.ebi.ac.uk/files/AF-Q06136-F1-model_v6.cif","pae_url":"https://alphafold.ebi.ac.uk/files/AF-Q06136-F1-predicted_aligned_error_v6.png","plddt_mean":95.38},"mouse_models":{"mgi_url":"https://www.informatics.jax.org/marker/summary?nomen=KDSR","jax_strain_url":"https://www.jax.org/strain/search?query=KDSR"},"sequence":{"accession":"Q06136","fasta_url":"https://rest.uniprot.org/uniprotkb/Q06136.fasta","uniprot_url":"https://www.uniprot.org/uniprotkb/Q06136/entry","alphafold_viewer_url":"https://alphafold.ebi.ac.uk/entry/Q06136"}},"corpus_meta":[{"pmid":"15328338","id":"PMC_15328338","title":"FVT-1 is a mammalian 3-ketodihydrosphingosine reductase with an active site that faces the cytosolic side of the endoplasmic reticulum membrane.","date":"2004","source":"The Journal of biological chemistry","url":"https://pubmed.ncbi.nlm.nih.gov/15328338","citation_count":80,"is_preprint":false},{"pmid":"28575652","id":"PMC_28575652","title":"Mutations in KDSR Cause Recessive Progressive Symmetric Erythrokeratoderma.","date":"2017","source":"American journal of human genetics","url":"https://pubmed.ncbi.nlm.nih.gov/28575652","citation_count":69,"is_preprint":false},{"pmid":"28774589","id":"PMC_28774589","title":"Biallelic Mutations in KDSR Disrupt Ceramide Synthesis and Result in a Spectrum of Keratinization Disorders Associated with Thrombocytopenia.","date":"2017","source":"The Journal of investigative dermatology","url":"https://pubmed.ncbi.nlm.nih.gov/28774589","citation_count":52,"is_preprint":false},{"pmid":"17420465","id":"PMC_17420465","title":"A missense mutation in the 3-ketodihydrosphingosine reductase FVT1 as candidate causal mutation for bovine spinal muscular atrophy.","date":"2007","source":"Proceedings of the National Academy of Sciences of the United States of America","url":"https://pubmed.ncbi.nlm.nih.gov/17420465","citation_count":41,"is_preprint":false},{"pmid":"8417785","id":"PMC_8417785","title":"FVT-1, a novel human transcription unit affected by variant translocation t(2;18)(p11;q21) of follicular lymphoma.","date":"1993","source":"Blood","url":"https://pubmed.ncbi.nlm.nih.gov/8417785","citation_count":40,"is_preprint":false},{"pmid":"30467204","id":"PMC_30467204","title":"Sphingolipid dysregulation due to lack of functional KDSR impairs proplatelet formation causing thrombocytopenia.","date":"2018","source":"Haematologica","url":"https://pubmed.ncbi.nlm.nih.gov/30467204","citation_count":33,"is_preprint":false},{"pmid":"19141869","id":"PMC_19141869","title":"Tsc10p and FVT1: topologically distinct short-chain reductases required for long-chain base synthesis in yeast and mammals.","date":"2009","source":"Journal of lipid research","url":"https://pubmed.ncbi.nlm.nih.gov/19141869","citation_count":23,"is_preprint":false},{"pmid":"34686882","id":"PMC_34686882","title":"Formation of keto-type ceramides in palmoplantar keratoderma based on biallelic KDSR mutations in patients.","date":"2022","source":"Human molecular genetics","url":"https://pubmed.ncbi.nlm.nih.gov/34686882","citation_count":14,"is_preprint":false},{"pmid":"32972506","id":"PMC_32972506","title":"A Homozygotic Mutation in KDSR may Cause Keratinization Disorders and Thrombocytopenia: A Case Report.","date":"2020","source":"Chinese medical sciences journal = Chung-kuo i hsueh k'o hsueh tsa chih","url":"https://pubmed.ncbi.nlm.nih.gov/32972506","citation_count":6,"is_preprint":false},{"pmid":"35958175","id":"PMC_35958175","title":"Case report: Compound heterozygous mutations in the KDSR gene cause progressive keratodermia and thrombocytopenia.","date":"2022","source":"Frontiers in pediatrics","url":"https://pubmed.ncbi.nlm.nih.gov/35958175","citation_count":2,"is_preprint":false},{"pmid":"36263748","id":"PMC_36263748","title":"Variable skin findings in two siblings with KDSR mutations manifesting in PERIOPTER syndrome.","date":"2022","source":"Pediatric dermatology","url":"https://pubmed.ncbi.nlm.nih.gov/36263748","citation_count":1,"is_preprint":false},{"pmid":"32714947","id":"PMC_32714947","title":"Spinal Muscular Atrophy in Blonde D'Aquitaine Calves Is Not Associated With FVT1 Gene Mutation.","date":"2020","source":"Frontiers in veterinary science","url":"https://pubmed.ncbi.nlm.nih.gov/32714947","citation_count":0,"is_preprint":false},{"pmid":"42105149","id":"PMC_42105149","title":"Vitamin D remodels the tumor microenvironment to suppress gastric cancer progression through cancer-associated fibroblasts-secreted exosomal miR-378c targeting KDSR.","date":"2026","source":"Archives of pharmacal research","url":"https://pubmed.ncbi.nlm.nih.gov/42105149","citation_count":0,"is_preprint":false}],"cost":{"stage1":{"model":"claude-sonnet-4-6","input_tokens":8322,"output_tokens":2157,"usd":0.02866,"stage1_stop_reason":"end_turn"},"stage2":{"model":"claude-opus-4-8","input_tokens":9192,"output_tokens":2324,"usd":0.05203,"stage2_stop_reason":"end_turn"},"total_usd":0.08069,"stage1_batch_id":"msgbatch_01BbTCMyrRPyhtEq6b1MdwCN","stage2_batch_id":"msgbatch_011dEed5bbxYvTAaQWKJevxu","note":"batch pricing = 50% of standard"},"stage1_raw":"```json\n{\n  \"discoveries\": [\n    {\n      \"year\": 2004,\n      \"finding\": \"Human FVT-1 (KDSR) functions as a 3-ketodihydrosphingosine (KDS) reductase: recombinant hFVT-1 exhibits NADPH-dependent KDS reductase activity in vitro, and forced expression in TSC10-null yeast suppresses growth defects, establishing it as the mammalian KDS reductase.\",\n      \"method\": \"In vitro enzyme assay with purified recombinant protein, yeast complementation (TSC10-null rescue), overexpression in cultured cells\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Strong — purified recombinant protein in vitro assay with NADPH dependence, plus yeast complementation as orthogonal functional validation, both in the same study\",\n      \"pmids\": [\"15328338\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2004,\n      \"finding\": \"hFVT-1 (KDSR) localizes to the endoplasmic reticulum, and the large hydrophilic domain containing putative active-site residues faces the cytosolic side of the ER membrane, indicating that KDS is reduced to dihydrosphingosine on the cytosolic face of the ER.\",\n      \"method\": \"Immunofluorescence microscopy (ER colocalization) and proteinase K digestion topology assay\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — two orthogonal methods (immunofluorescence + protease protection assay) in one rigorous study establishing ER localization and active-site topology\",\n      \"pmids\": [\"15328338\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2009,\n      \"finding\": \"FVT1 (KDSR) is the principal 3-ketosphinganine reductase in mammalian cells: siRNA silencing of FVT1 directly reduced cellular reductase activity in proportion to FVT1 levels. The N-terminal membrane-spanning domain of FVT1 (absent in yeast Tsc10p) targets it to the ER lumen and confers distinct topology relative to yeast Tsc10p. Mutation of conserved catalytic residues differentially affected FVT1 vs. Tsc10p activity, revealing mechanistic differences between the two orthologs.\",\n      \"method\": \"siRNA knockdown with enzymatic activity measurement; N-terminal GFP fusion for ER-targeting domain mapping; factor Xa protease domain removal; active-site mutagenesis\",\n      \"journal\": \"Journal of lipid research\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1–2 / Strong — multiple orthogonal methods (knockdown + activity assay, GFP fusion targeting, protease digestion, mutagenesis) in one study establishing principal reductase role and mechanistic details\",\n      \"pmids\": [\"19141869\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2007,\n      \"finding\": \"A missense mutation (Ala-175→Thr) in bovine FVT1 (KDSR) abolishes 3-ketodihydrosphingosine reductase activity in vitro, yet the mutant protein retains sufficient residual in vivo activity to complement a yeast knockout, explaining why SMA-affected calves are viable but develop neuron-specific degeneration.\",\n      \"method\": \"In vitro enzyme assay comparing Ala-175 vs. Thr-175 variants; yeast complementation assay\",\n      \"journal\": \"Proceedings of the National Academy of Sciences of the United States of America\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Moderate — in vitro enzymatic activity assay with defined mutation plus orthogonal yeast complementation, single lab but rigorous biochemical controls\",\n      \"pmids\": [\"17420465\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2017,\n      \"finding\": \"Loss-of-function mutations in KDSR reduce ceramide levels in skin and impair KDSR enzymatic activity, causing defective acylceramide synthesis and leading to skin hyperkeratosis; thrombocytopenia is also present, indicating KDSR activity is required for normal platelet function.\",\n      \"method\": \"Whole-exome sequencing identifying mutations; KDSR enzymatic activity measurement in patient samples; ceramide level quantification in skin\",\n      \"journal\": \"The Journal of investigative dermatology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — enzymatic activity measured in patient-derived material, ceramide metabolite profiling, but no reconstitution experiment; single lab\",\n      \"pmids\": [\"28774589\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2017,\n      \"finding\": \"KDSR mutations causing exon skipping (including a recurrent silent third-base change) disrupt KDSR function as demonstrated by yeast complementation failure, establishing that loss of KDSR enzymatic activity underlies progressive symmetric erythrokeratoderma.\",\n      \"method\": \"Splicing assay (cDNA sequencing), yeast complementation, immunohistochemistry\",\n      \"journal\": \"American journal of human genetics\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — yeast complementation as functional readout plus splicing assay; multiple orthogonal approaches in one study but patient-based rather than reconstituted\",\n      \"pmids\": [\"28575652\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2018,\n      \"finding\": \"KDSR insufficiency impairs proplatelet formation from megakaryocytes: CD34+-derived megakaryocytes from KDSR-deficient patients showed hyperproliferation and reduced proplatelet formation, reversed by re-expression of functional KDSR in iPSC-derived megakaryocytes. Kdsr depletion in zebrafish recapitulated thrombocytopenia. A compensatory in vivo pathway partially normalizes downstream ceramide levels.\",\n      \"method\": \"CD34+ stem cell-derived megakaryocyte culture, iPSC differentiation with KDSR rescue, zebrafish kdsr morpholino knockdown, broad metabolomics screen\",\n      \"journal\": \"Haematologica\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — rescue experiment (iPSC + functional KDSR re-expression), zebrafish model replication, metabolomics; multiple orthogonal methods across human and animal models\",\n      \"pmids\": [\"30467204\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2022,\n      \"finding\": \"In patients with biallelic KDSR mutations, the KDSR substrate 3-ketodihydrosphingosine accumulates and is processed by ceramide synthases to produce novel keto-type ceramides (up to 10% of ceramide species) in the stratum corneum, revealing a bypass pathway when KDSR is non-functional and demonstrating that tight intermediate regulation during sphingolipid anabolism is required for normal ceramide composition.\",\n      \"method\": \"Stratum corneum lipid analysis by mass spectrometry in KDSR-mutant patients vs. controls; structural identification of keto-type ceramides\",\n      \"journal\": \"Human molecular genetics\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — novel lipid species identified by mass spectrometry in patient tissue; mechanistically informative but patient-based, not reconstituted biochemistry\",\n      \"pmids\": [\"34686882\"],\n      \"is_preprint\": false\n    }\n  ],\n  \"current_model\": \"KDSR (FVT1) encodes an NADPH-dependent 3-ketodihydrosphingosine reductase that is an integral endoplasmic reticulum membrane protein with its catalytic domain facing the cytosol; it is the principal enzyme catalyzing the second step of de novo ceramide/sphingolipid biosynthesis (conversion of 3-ketodihydrosphingosine to dihydrosphingosine/sphinganine), and its loss of function—through missense, splice, or frameshift mutations—disrupts ceramide production, causes accumulation of novel keto-type ceramide species, and leads to keratinization disorders, while also impairing megakaryocyte proplatelet formation and resulting in thrombocytopenia.\"\n}\n```","stage2_raw":"{\n  \"mechanistic_narrative\": \"KDSR (FVT1) is the principal mammalian NADPH-dependent 3-ketodihydrosphingosine reductase, catalyzing the second step of de novo sphingolipid biosynthesis by reducing 3-ketodihydrosphingosine to dihydrosphingosine [#0, #2]. It is an integral endoplasmic reticulum membrane protein in which an N-terminal membrane-spanning domain anchors a large hydrophilic catalytic domain on the cytosolic face of the ER, defining where this reduction occurs [#1, #2]. Loss-of-function mutations abolish or reduce reductase activity and lower ceramide levels in skin, causing defective acylceramide synthesis and keratinization disorders including progressive symmetric erythrokeratoderma [#4, #5]; KDSR deficiency also impairs proplatelet formation from megakaryocytes, with patient megakaryocytes showing hyperproliferation and reduced proplatelet output that is rescued by re-expression of functional KDSR, and is accompanied by thrombocytopenia [#6]. When KDSR is non-functional, its accumulated substrate is shunted through ceramide synthases to generate novel keto-type ceramide species in the stratum corneum, revealing a bypass pathway that partially compensates downstream lipid levels [#6, #7].\",\n  \"teleology\": [\n    {\n      \"year\": 2004,\n      \"claim\": \"Established the molecular identity and enzymatic activity of human FVT1/KDSR, answering whether it served as the mammalian counterpart to yeast Tsc10p in sphingolipid synthesis.\",\n      \"evidence\": \"In vitro NADPH-dependent reductase assay with recombinant protein and TSC10-null yeast complementation\",\n      \"pmids\": [\"15328338\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Did not establish in vivo contribution relative to other reductases\", \"No structural model of the catalytic site\"]\n    },\n    {\n      \"year\": 2004,\n      \"claim\": \"Defined the subcellular localization and membrane topology, showing the reaction occurs on the cytosolic face of the ER.\",\n      \"evidence\": \"Immunofluorescence ER colocalization and proteinase K protection topology assay\",\n      \"pmids\": [\"15328338\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Topology assignment refined in later work (lumenal vs cytosolic active-site orientation)\", \"Membrane insertion mechanism not addressed\"]\n    },\n    {\n      \"year\": 2007,\n      \"claim\": \"Linked a specific missense substitution to disease by showing it abolishes in vitro activity while retaining residual in vivo function, explaining a tissue-restricted degenerative phenotype.\",\n      \"evidence\": \"In vitro activity comparison of bovine Ala-175 vs Thr-175 variants and yeast complementation\",\n      \"pmids\": [\"17420465\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Mechanism of neuron-specific vulnerability not resolved\", \"Human relevance of bovine variant not directly tested\"]\n    },\n    {\n      \"year\": 2009,\n      \"claim\": \"Demonstrated KDSR is the principal cellular 3-ketosphinganine reductase and mapped the N-terminal ER-targeting domain, clarifying mechanistic divergence from yeast Tsc10p.\",\n      \"evidence\": \"siRNA knockdown with activity measurement, GFP-fusion targeting, protease domain removal, and catalytic-residue mutagenesis\",\n      \"pmids\": [\"19141869\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Functional consequence of distinct topology not fully defined\", \"No structural basis for catalytic-residue differences\"]\n    },\n    {\n      \"year\": 2017,\n      \"claim\": \"Connected biallelic KDSR loss of function to human keratinization disease through reduced enzymatic activity, lowered skin ceramide, and concurrent thrombocytopenia.\",\n      \"evidence\": \"Whole-exome sequencing, patient-sample reductase activity, skin ceramide quantification, and splicing/yeast complementation assays\",\n      \"pmids\": [\"28774589\", \"28575652\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"No reconstitution of mutant enzymes in defined system\", \"Genotype-phenotype severity relationship incompletely mapped\"]\n    },\n    {\n      \"year\": 2018,\n      \"claim\": \"Established a cell-autonomous role for KDSR in megakaryocyte proplatelet formation and validated causality through rescue and an animal model.\",\n      \"evidence\": \"Patient CD34+/iPSC-derived megakaryocyte culture with functional KDSR re-expression, zebrafish kdsr morpholino knockdown, and metabolomics\",\n      \"pmids\": [\"30467204\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Identity of the compensatory in vivo pathway not defined\", \"Molecular link between ceramide deficit and proplatelet defect unresolved\"]\n    },\n    {\n      \"year\": 2022,\n      \"claim\": \"Revealed a substrate-shunting bypass in which accumulated 3-ketodihydrosphingosine is converted into novel keto-type ceramides, explaining altered skin ceramide composition under KDSR loss.\",\n      \"evidence\": \"Mass spectrometry lipidomics and structural identification of keto-ceramides in patient stratum corneum\",\n      \"pmids\": [\"34686882\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Enzymes responsible for keto-ceramide production not directly identified\", \"Functional impact of keto-ceramides on skin barrier not established\"]\n    },\n    {\n      \"year\": null,\n      \"claim\": \"The structural basis of catalysis and the molecular mechanism linking ceramide deficiency to tissue-specific phenotypes (skin, platelets, neurons) remain unresolved.\",\n      \"evidence\": \"\",\n      \"pmids\": [],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"No high-resolution structure of human KDSR\", \"Compensatory bypass pathway and its regulators uncharacterized\", \"Mechanistic basis for tissue selectivity of phenotypes unknown\"]\n    }\n  ],\n  \"mechanism_profile\": {\n    \"molecular_activity\": [\n      {\"term_id\": \"GO:0016491\", \"supporting_discovery_ids\": [0, 2, 3]}\n    ],\n    \"localization\": [\n      {\"term_id\": \"GO:0005783\", \"supporting_discovery_ids\": [1, 2]}\n    ],\n    \"pathway\": [\n      {\"term_id\": \"R-HSA-1430728\", \"supporting_discovery_ids\": [0, 4, 7]}\n    ],\n    \"complexes\": [],\n    \"partners\": [],\n    \"other_free_text\": []\n  }\n}","audit_flag":null,"evaluation":{"pairwise":"win","faith_supported":4,"faith_total":4,"faith_pct":100.0}}