{"gene":"SFXN4","run_date":"2026-06-10T07:46:31","timeline":{"discoveries":[{"year":2013,"finding":"SFXN4 localizes to the mitochondrial inner membrane and is required for mitochondrial respiratory homeostasis and erythropoiesis; loss-of-function mutations cause mitochondrial respiratory defects and macrocytic anemia, demonstrated by sfxn4 knockdown in zebrafish and in vitro/in vivo complementation with patient fibroblasts.","method":"Exome sequencing, zebrafish morpholino knockdown, in vitro and in vivo complementation studies with patient fibroblasts","journal":"American journal of human genetics","confidence":"High","confidence_rationale":"Tier 2 / Strong — reciprocal in vitro and in vivo complementation, zebrafish KD with specific phenotypic readout, replicated across two affected individuals and multiple model systems","pmids":["24119684"],"is_preprint":false},{"year":2019,"finding":"SFXN4 knockout reduces Fe-S cluster formation, diminishes mitochondrial respiratory chain complex stability and activity, causes a shift to glycolytic metabolism, affects the cytosolic aconitase-IRP1 switch, redistributes iron from cytosol to mitochondria, reduces ferrochelatase levels, and inhibits translation of ALAS2.","method":"SFXN4 knockout cell lines, Fe-S cluster activity assays, metabolic flux analysis (glycolysis vs. respiration), immunoblot for ferrochelatase, ALAS2 translation assay","journal":"Scientific reports","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — multiple orthogonal assays in a single lab, KO with defined molecular phenotypes","pmids":["31873120"],"is_preprint":false},{"year":2022,"finding":"SFXN4 functions as a complex I assembly factor that interacts with the MCIA (Mitochondrial Complex I Assembly) complex and is specifically required for assembly of the ND2 module of mitochondrial complex I.","method":"Co-immunoprecipitation, complexome profiling, SFXN4 KO cell lines with complex I assembly assays, interaction studies with MCIA complex components","journal":"Proceedings of the National Academy of Sciences of the United States of America","confidence":"High","confidence_rationale":"Tier 2 / Strong — reciprocal Co-IP, complexomics, KO with defined assembly defect, published in peer-reviewed journal with multiple orthogonal methods","pmids":["35333655"],"is_preprint":false},{"year":2022,"finding":"SFXN4 knockdown in ovarian cancer cells inhibits Fe-S cluster biogenesis, leading to accumulation of excess iron and oxidative stress, and reduces activity of Fe-S-dependent DNA repair enzymes, thereby sensitizing cells to DNA-damaging agents and PARP inhibitors; SFXN4 knockout inhibits tumor growth in a mouse xenograft model.","method":"siRNA knockdown, Fe-S cluster activity assays, ROS measurements, DNA repair assays, cisplatin/PARP inhibitor sensitivity assays, mouse xenograft tumor growth experiments","journal":"Scientific reports","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — multiple orthogonal methods in single lab (KD, KO, in vitro and in vivo models), mechanistic pathway placement","pmids":["36402786"],"is_preprint":false},{"year":2019,"finding":"SFXN4 loss-of-function mutations cause complex I enzyme activity deficiency with loss of complex I subunit proteins and ultrastructural mitochondrial abnormalities, as shown in muscle tissue from a patient with bi-allelic SFXN4 mutations.","method":"Whole-exome sequencing, mitochondrial enzyme activity assays, immunoblot for complex I subunit proteins, electron microscopy of muscle, mRNA expression analysis","journal":"Mitochondrion","confidence":"Medium","confidence_rationale":"Tier 2 / Weak — single case with direct biochemical and structural measurements, but single lab/single case","pmids":["31059822"],"is_preprint":false},{"year":2003,"finding":"SFXN4 encodes a 305-amino acid protein with a predicted five-transmembrane-domain structure, consistent with a mitochondrial transporter, and is expressed in many tissues.","method":"cDNA cloning from human fetal brain library, sequence analysis, RT-PCR expression profiling, genomic mapping","journal":"DNA sequence : the journal of DNA sequencing and mapping","confidence":"Low","confidence_rationale":"Tier 4 / Weak — computational structural prediction and expression survey, no functional assay performed","pmids":["14756423"],"is_preprint":false},{"year":2023,"finding":"In CLPP-deficient mouse testis, SFXN4 accumulates alongside COX15 as a complex IV metal-binding assembly factor co-accumulating with heavy metals (iron, molybdenum, cobalt, manganese), suggesting SFXN4 participates in mitochondrial metal/iron handling during complex assembly.","method":"Complexome profiling (complexomics), heavy metal quantification, immunoblot validation in mouse tissue","journal":"International journal of molecular sciences","confidence":"Low","confidence_rationale":"Tier 3 / Weak — SFXN4 accumulation observed in a model of a different disease (CLPP deficiency), single lab, not directly tested for function","pmids":["38139332"],"is_preprint":false},{"year":2025,"finding":"SFXN4 is implicated in mitochondrial iron regulation, heme biosynthesis, and iron-sulfur cluster assembly, with SFXN1 and SFXN3 specializing in serine transport while SFXN2 and SFXN4 specialize in iron-related functions; SFXNs share conserved transmembrane domains critical for substrate transport.","method":"Comparative genomics and literature review of family function; structural domain analysis","journal":"Human genomics","confidence":"Low","confidence_rationale":"Tier 4 / Weak — review/annotation paper, no new experiments directly on SFXN4 reported","pmids":["40542427"],"is_preprint":false}],"current_model":"SFXN4 is a five-transmembrane inner mitochondrial membrane protein that functions as a complex I assembly factor by interacting with the MCIA complex and facilitating assembly of the ND2 module; it is also essential for Fe-S cluster biogenesis, mitochondrial iron homeostasis, and respiratory chain function, with loss-of-function causing complex I deficiency, impaired Fe-S cluster formation, iron redistribution to mitochondria, and defects in heme synthesis (reduced ferrochelatase and ALAS2 translation), collectively explaining why SFXN4 mutations cause mitochondrial disease with macrocytic anemia."},"narrative":{"mechanistic_narrative":"SFXN4 is a mitochondrial inner membrane protein essential for respiratory chain function and erythropoiesis, with loss-of-function mutations causing mitochondrial disease accompanied by macrocytic anemia [PMID:24119684]. Mechanistically, SFXN4 acts as a complex I assembly factor: it interacts with the MCIA (Mitochondrial Complex I Assembly) complex and is specifically required for assembly of the ND2 module, such that its loss produces complex I enzyme deficiency and depletion of complex I subunit proteins [PMID:35333655, PMID:31059822]. SFXN4 is independently required for iron-sulfur (Fe-S) cluster biogenesis, and its loss diminishes respiratory chain complex stability, shifts metabolism toward glycolysis, perturbs the cytosolic aconitase-IRP1 switch, redistributes iron from cytosol to mitochondria, and impairs heme synthesis through reduced ferrochelatase levels and inhibited ALAS2 translation — connecting its molecular activity to the anemia phenotype [PMID:31873120]. Disruption of Fe-S-dependent processes downstream of SFXN4 loss extends to DNA repair enzymes, and SFXN4 depletion sensitizes ovarian cancer cells to DNA-damaging agents and PARP inhibitors while restraining tumor growth in xenografts [PMID:36402786].","teleology":[{"year":2013,"claim":"Established SFXN4 as a disease gene by linking its loss to mitochondrial respiratory failure and macrocytic anemia, framing it as a respiratory homeostasis factor rather than a bystander locus.","evidence":"Exome sequencing of affected individuals with reciprocal in vitro and in vivo complementation and zebrafish morpholino knockdown","pmids":["24119684"],"confidence":"High","gaps":["No molecular mechanism for how SFXN4 supports respiration identified","Connection between respiratory defect and anemia not resolved at this stage"]},{"year":2019,"claim":"Placed SFXN4 upstream of Fe-S cluster biogenesis and iron/heme handling, explaining how its loss could simultaneously cripple respiration and erythropoiesis.","evidence":"SFXN4 knockout cell lines with Fe-S activity assays, metabolic flux analysis, and ferrochelatase/ALAS2 readouts; plus a patient muscle study with biochemical and ultrastructural complex I deficiency","pmids":["31873120","31059822"],"confidence":"Medium","gaps":["Whether SFXN4 directly catalyzes Fe-S assembly or acts indirectly not distinguished","Mechanism linking SFXN4 to ALAS2 translational control unknown","Patient findings rest on a single case"]},{"year":2022,"claim":"Defined a direct molecular role for SFXN4 as a complex I assembly factor acting through the MCIA complex at the ND2 module, providing a concrete mechanism for the complex I deficiency.","evidence":"Reciprocal Co-immunoprecipitation, complexome profiling, and SFXN4 KO complex I assembly assays","pmids":["35333655"],"confidence":"High","gaps":["How a putative transporter contributes to module assembly is unresolved","Relationship between the assembly role and the Fe-S/iron role not reconciled"]},{"year":2022,"claim":"Extended the consequences of SFXN4-dependent Fe-S biogenesis to genome maintenance and identified a therapeutic vulnerability in cancer.","evidence":"siRNA knockdown and KO with Fe-S/ROS assays, DNA repair and drug-sensitivity assays, and mouse xenograft tumor growth experiments","pmids":["36402786"],"confidence":"Medium","gaps":["Which specific Fe-S DNA repair enzymes are rate-limiting not defined","Single-lab findings without independent replication"]},{"year":null,"claim":"The transport substrate of SFXN4 and how a single protein integrates complex I ND2-module assembly with Fe-S cluster biogenesis and iron homeostasis remain unresolved.","evidence":"","pmids":[],"confidence":"Low","gaps":["No demonstrated transported substrate for SFXN4","No structural model of SFXN4 within the MCIA complex","Mechanistic link between assembly function and iron/Fe-S function not established"]}],"mechanism_profile":{"molecular_activity":[{"term_id":"GO:0005215","term_label":"transporter activity","supporting_discovery_ids":[5,7]}],"localization":[{"term_id":"GO:0005739","term_label":"mitochondrion","supporting_discovery_ids":[0,5]}],"pathway":[{"term_id":"R-HSA-1430728","term_label":"Metabolism","supporting_discovery_ids":[1,2]},{"term_id":"R-HSA-1852241","term_label":"Organelle biogenesis and maintenance","supporting_discovery_ids":[2]}],"complexes":["MCIA complex"],"partners":[],"other_free_text":[]}},"prefetch_data":{"uniprot":{"accession":"Q6P4A7","full_name":"Sideroflexin-4","aliases":["Breast cancer resistance marker 1"],"length_aa":337,"mass_kda":38.0,"function":"Mitochondrial amino-acid transporter (By similarity). Does not act as a serine transporter: not able to mediate transport of serine into mitochondria (PubMed:30442778)","subcellular_location":"Mitochondrion inner membrane","url":"https://www.uniprot.org/uniprotkb/Q6P4A7/entry"},"depmap":{"release":"DepMap","has_data":true,"is_common_essential":false,"resolved_as":"","url":"https://depmap.org/portal/gene/SFXN4","classification":"Not Classified","n_dependent_lines":9,"n_total_lines":1208,"dependency_fraction":0.0074503311258278145},"opencell":{"profiled":false,"resolved_as":"","ensg_id":"","cell_line_id":"","localizations":[],"interactors":[],"url":"https://opencell.sf.czbiohub.org/search/SFXN4","total_profiled":1310},"omim":[{"mim_id":"615578","title":"COMBINED OXIDATIVE PHOSPHORYLATION DEFICIENCY 18; COXPD18","url":"https://www.omim.org/entry/615578"},{"mim_id":"615564","title":"SIDEROFLEXIN 4; SFXN4","url":"https://www.omim.org/entry/615564"},{"mim_id":"609060","title":"COMBINED OXIDATIVE PHOSPHORYLATION DEFICIENCY 1; COXPD1","url":"https://www.omim.org/entry/609060"}],"hpa":{"profiled":true,"resolved_as":"","reliability":"Approved","locations":[{"location":"Nucleoplasm","reliability":"Approved"},{"location":"Mitochondria","reliability":"Approved"},{"location":"Vesicles","reliability":"Additional"}],"tissue_specificity":"Low tissue specificity","tissue_distribution":"Detected in all","driving_tissues":[],"url":"https://www.proteinatlas.org/search/SFXN4"},"hgnc":{"alias_symbol":["SLC56A4"],"prev_symbol":[]},"alphafold":{"accession":"Q6P4A7","domains":[{"cath_id":"-","chopping":"28-95","consensus_level":"medium","plddt":84.4538,"start":28,"end":95},{"cath_id":"-","chopping":"107-335","consensus_level":"high","plddt":90.6538,"start":107,"end":335}],"viewer_url":"https://alphafold.ebi.ac.uk/entry/Q6P4A7","model_url":"https://alphafold.ebi.ac.uk/files/AF-Q6P4A7-F1-model_v6.cif","pae_url":"https://alphafold.ebi.ac.uk/files/AF-Q6P4A7-F1-predicted_aligned_error_v6.png","plddt_mean":85.38},"mouse_models":{"mgi_url":"https://www.informatics.jax.org/marker/summary?nomen=SFXN4","jax_strain_url":"https://www.jax.org/strain/search?query=SFXN4"},"sequence":{"accession":"Q6P4A7","fasta_url":"https://rest.uniprot.org/uniprotkb/Q6P4A7.fasta","uniprot_url":"https://www.uniprot.org/uniprotkb/Q6P4A7/entry","alphafold_viewer_url":"https://alphafold.ebi.ac.uk/entry/Q6P4A7"}},"corpus_meta":[{"pmid":"24119684","id":"PMC_24119684","title":"Macrocytic anemia and mitochondriopathy resulting from a defect in sideroflexin 4.","date":"2013","source":"American journal of human genetics","url":"https://pubmed.ncbi.nlm.nih.gov/24119684","citation_count":56,"is_preprint":false},{"pmid":"31873120","id":"PMC_31873120","title":"Sideroflexin 4 affects Fe-S cluster biogenesis, iron metabolism, mitochondrial respiration and heme biosynthetic enzymes.","date":"2019","source":"Scientific reports","url":"https://pubmed.ncbi.nlm.nih.gov/31873120","citation_count":44,"is_preprint":false},{"pmid":"32693751","id":"PMC_32693751","title":"Genome-Wide Association Study Meta-Analysis of Stroke in 22 000 Individuals of African Descent Identifies Novel Associations With Stroke.","date":"2020","source":"Stroke","url":"https://pubmed.ncbi.nlm.nih.gov/32693751","citation_count":28,"is_preprint":false},{"pmid":"35333655","id":"PMC_35333655","title":"Sideroflexin 4 is a complex I assembly factor that interacts with the MCIA complex and is required for the assembly of the ND2 module.","date":"2022","source":"Proceedings of the National Academy of Sciences of the United States of America","url":"https://pubmed.ncbi.nlm.nih.gov/35333655","citation_count":23,"is_preprint":false},{"pmid":"14756423","id":"PMC_14756423","title":"Molecular cloning and characterization of a novel human putative transmembrane protein homologous to mouse sideroflexin associated with sideroblastic anemia.","date":"2003","source":"DNA sequence : the journal of DNA sequencing and mapping","url":"https://pubmed.ncbi.nlm.nih.gov/14756423","citation_count":20,"is_preprint":false},{"pmid":"34749647","id":"PMC_34749647","title":"Trait correlated expression combined with eQTL and ASE analyses identified novel candidate genes affecting intramuscular fat.","date":"2021","source":"BMC genomics","url":"https://pubmed.ncbi.nlm.nih.gov/34749647","citation_count":17,"is_preprint":false},{"pmid":"34985130","id":"PMC_34985130","title":"Hereditary myopathies associated with hematological abnormalities.","date":"2022","source":"Muscle & nerve","url":"https://pubmed.ncbi.nlm.nih.gov/34985130","citation_count":11,"is_preprint":false},{"pmid":"36402786","id":"PMC_36402786","title":"Complementary anti-cancer pathways triggered by inhibition of sideroflexin 4 in ovarian cancer.","date":"2022","source":"Scientific reports","url":"https://pubmed.ncbi.nlm.nih.gov/36402786","citation_count":10,"is_preprint":false},{"pmid":"31059822","id":"PMC_31059822","title":"[Prenatal onset of mitochondrial disease is associated with sideroflexin 4 deficiency].","date":"2019","source":"Mitochondrion","url":"https://pubmed.ncbi.nlm.nih.gov/31059822","citation_count":10,"is_preprint":false},{"pmid":"37786439","id":"PMC_37786439","title":"Comprehensive Analysis of Sideroflexin 4 in Hepatocellular Carcinoma by Bioinformatics and Experiments.","date":"2023","source":"International journal of medical sciences","url":"https://pubmed.ncbi.nlm.nih.gov/37786439","citation_count":9,"is_preprint":false},{"pmid":"31988005","id":"PMC_31988005","title":"Interactome networks between the human respiratory syncytial virus (HRSV), the human metapneumovirus (ΗMPV), and their host: In silico investigation and comparative functional enrichment analysis.","date":"2020","source":"Microbial pathogenesis","url":"https://pubmed.ncbi.nlm.nih.gov/31988005","citation_count":8,"is_preprint":false},{"pmid":"32772906","id":"PMC_32772906","title":"Transcriptome-wide Association Study Identifies Genetically Dysregulated Genes in Diabetic Neuropathy.","date":"2021","source":"Combinatorial chemistry & high throughput screening","url":"https://pubmed.ncbi.nlm.nih.gov/32772906","citation_count":5,"is_preprint":false},{"pmid":"38139332","id":"PMC_38139332","title":"Translation Fidelity and Respiration Deficits in CLPP-Deficient Tissues: Mechanistic Insights from Mitochondrial Complexome Profiling.","date":"2023","source":"International journal of molecular sciences","url":"https://pubmed.ncbi.nlm.nih.gov/38139332","citation_count":5,"is_preprint":false},{"pmid":"40542427","id":"PMC_40542427","title":"Update of the sideroflexin (SLC56) gene family.","date":"2025","source":"Human genomics","url":"https://pubmed.ncbi.nlm.nih.gov/40542427","citation_count":4,"is_preprint":false},{"pmid":"40777745","id":"PMC_40777745","title":"Multi-omics integrative analysis reveals novel genetic loci and candidate genes for ischemic stroke.","date":"2025","source":"Molecular therapy. Nucleic acids","url":"https://pubmed.ncbi.nlm.nih.gov/40777745","citation_count":4,"is_preprint":false},{"pmid":"35300139","id":"PMC_35300139","title":"Screening and Analysis of Potential Critical Gene in Acute Myocardial Infarction Based on a miRNA-mRNA Regulatory Network.","date":"2022","source":"International journal of general medicine","url":"https://pubmed.ncbi.nlm.nih.gov/35300139","citation_count":4,"is_preprint":false},{"pmid":"38355435","id":"PMC_38355435","title":"Exploring the novel duo of Reticulocalbin, and Sideroflexin as future biomarker candidates for Exacerbated Chronic Obstructive Pulmonary Disease.","date":"2024","source":"Clinical proteomics","url":"https://pubmed.ncbi.nlm.nih.gov/38355435","citation_count":2,"is_preprint":false},{"pmid":"39915876","id":"PMC_39915876","title":"Sideroflexin family genes were dysregulated and associated with tumor progression in prostate cancers.","date":"2025","source":"Human genomics","url":"https://pubmed.ncbi.nlm.nih.gov/39915876","citation_count":2,"is_preprint":false},{"pmid":"41167676","id":"PMC_41167676","title":"Expression and Clinical Significance of Sideroflexin 4 (SFXN4) in Colorectal Cancer.","date":"2025","source":"In vivo (Athens, Greece)","url":"https://pubmed.ncbi.nlm.nih.gov/41167676","citation_count":0,"is_preprint":false},{"pmid":"41713566","id":"PMC_41713566","title":"Phenotypic description and functional characterization of the mitochondrial disease associated with the SFXN4 gene.","date":"2026","source":"Mitochondrion","url":"https://pubmed.ncbi.nlm.nih.gov/41713566","citation_count":0,"is_preprint":false},{"pmid":"41343408","id":"PMC_41343408","title":"Construction and validation of an oxidative phosphorylation-related gene signature in lung squamous cell carcinoma patients.","date":"2025","source":"Lung cancer management","url":"https://pubmed.ncbi.nlm.nih.gov/41343408","citation_count":0,"is_preprint":false},{"pmid":"40292254","id":"PMC_40292254","title":"Dynamic changes in lactate-related genes in microglia and their role in immune cell interactions after ischemic stroke.","date":"2025","source":"Open medicine (Warsaw, Poland)","url":"https://pubmed.ncbi.nlm.nih.gov/40292254","citation_count":0,"is_preprint":false}],"cost":{"stage1":{"model":"claude-sonnet-4-6","input_tokens":12782,"output_tokens":1889,"usd":0.033341,"stage1_stop_reason":"end_turn"},"stage2":{"model":"claude-opus-4-8","input_tokens":8902,"output_tokens":1917,"usd":0.046218,"stage2_stop_reason":"end_turn"},"total_usd":0.079559,"stage1_batch_id":"msgbatch_013LWZZT6MWaqB9qyTSeQBmU","stage2_batch_id":"msgbatch_0194ZzQaTGNpruoNJBbEMbt3","note":"batch pricing = 50% of standard"},"stage1_raw":"```json\n{\n  \"discoveries\": [\n    {\n      \"year\": 2013,\n      \"finding\": \"SFXN4 localizes to the mitochondrial inner membrane and is required for mitochondrial respiratory homeostasis and erythropoiesis; loss-of-function mutations cause mitochondrial respiratory defects and macrocytic anemia, demonstrated by sfxn4 knockdown in zebrafish and in vitro/in vivo complementation with patient fibroblasts.\",\n      \"method\": \"Exome sequencing, zebrafish morpholino knockdown, in vitro and in vivo complementation studies with patient fibroblasts\",\n      \"journal\": \"American journal of human genetics\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — reciprocal in vitro and in vivo complementation, zebrafish KD with specific phenotypic readout, replicated across two affected individuals and multiple model systems\",\n      \"pmids\": [\"24119684\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2019,\n      \"finding\": \"SFXN4 knockout reduces Fe-S cluster formation, diminishes mitochondrial respiratory chain complex stability and activity, causes a shift to glycolytic metabolism, affects the cytosolic aconitase-IRP1 switch, redistributes iron from cytosol to mitochondria, reduces ferrochelatase levels, and inhibits translation of ALAS2.\",\n      \"method\": \"SFXN4 knockout cell lines, Fe-S cluster activity assays, metabolic flux analysis (glycolysis vs. respiration), immunoblot for ferrochelatase, ALAS2 translation assay\",\n      \"journal\": \"Scientific reports\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — multiple orthogonal assays in a single lab, KO with defined molecular phenotypes\",\n      \"pmids\": [\"31873120\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2022,\n      \"finding\": \"SFXN4 functions as a complex I assembly factor that interacts with the MCIA (Mitochondrial Complex I Assembly) complex and is specifically required for assembly of the ND2 module of mitochondrial complex I.\",\n      \"method\": \"Co-immunoprecipitation, complexome profiling, SFXN4 KO cell lines with complex I assembly assays, interaction studies with MCIA complex components\",\n      \"journal\": \"Proceedings of the National Academy of Sciences of the United States of America\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — reciprocal Co-IP, complexomics, KO with defined assembly defect, published in peer-reviewed journal with multiple orthogonal methods\",\n      \"pmids\": [\"35333655\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2022,\n      \"finding\": \"SFXN4 knockdown in ovarian cancer cells inhibits Fe-S cluster biogenesis, leading to accumulation of excess iron and oxidative stress, and reduces activity of Fe-S-dependent DNA repair enzymes, thereby sensitizing cells to DNA-damaging agents and PARP inhibitors; SFXN4 knockout inhibits tumor growth in a mouse xenograft model.\",\n      \"method\": \"siRNA knockdown, Fe-S cluster activity assays, ROS measurements, DNA repair assays, cisplatin/PARP inhibitor sensitivity assays, mouse xenograft tumor growth experiments\",\n      \"journal\": \"Scientific reports\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — multiple orthogonal methods in single lab (KD, KO, in vitro and in vivo models), mechanistic pathway placement\",\n      \"pmids\": [\"36402786\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2019,\n      \"finding\": \"SFXN4 loss-of-function mutations cause complex I enzyme activity deficiency with loss of complex I subunit proteins and ultrastructural mitochondrial abnormalities, as shown in muscle tissue from a patient with bi-allelic SFXN4 mutations.\",\n      \"method\": \"Whole-exome sequencing, mitochondrial enzyme activity assays, immunoblot for complex I subunit proteins, electron microscopy of muscle, mRNA expression analysis\",\n      \"journal\": \"Mitochondrion\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Weak — single case with direct biochemical and structural measurements, but single lab/single case\",\n      \"pmids\": [\"31059822\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2003,\n      \"finding\": \"SFXN4 encodes a 305-amino acid protein with a predicted five-transmembrane-domain structure, consistent with a mitochondrial transporter, and is expressed in many tissues.\",\n      \"method\": \"cDNA cloning from human fetal brain library, sequence analysis, RT-PCR expression profiling, genomic mapping\",\n      \"journal\": \"DNA sequence : the journal of DNA sequencing and mapping\",\n      \"confidence\": \"Low\",\n      \"confidence_rationale\": \"Tier 4 / Weak — computational structural prediction and expression survey, no functional assay performed\",\n      \"pmids\": [\"14756423\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2023,\n      \"finding\": \"In CLPP-deficient mouse testis, SFXN4 accumulates alongside COX15 as a complex IV metal-binding assembly factor co-accumulating with heavy metals (iron, molybdenum, cobalt, manganese), suggesting SFXN4 participates in mitochondrial metal/iron handling during complex assembly.\",\n      \"method\": \"Complexome profiling (complexomics), heavy metal quantification, immunoblot validation in mouse tissue\",\n      \"journal\": \"International journal of molecular sciences\",\n      \"confidence\": \"Low\",\n      \"confidence_rationale\": \"Tier 3 / Weak — SFXN4 accumulation observed in a model of a different disease (CLPP deficiency), single lab, not directly tested for function\",\n      \"pmids\": [\"38139332\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2025,\n      \"finding\": \"SFXN4 is implicated in mitochondrial iron regulation, heme biosynthesis, and iron-sulfur cluster assembly, with SFXN1 and SFXN3 specializing in serine transport while SFXN2 and SFXN4 specialize in iron-related functions; SFXNs share conserved transmembrane domains critical for substrate transport.\",\n      \"method\": \"Comparative genomics and literature review of family function; structural domain analysis\",\n      \"journal\": \"Human genomics\",\n      \"confidence\": \"Low\",\n      \"confidence_rationale\": \"Tier 4 / Weak — review/annotation paper, no new experiments directly on SFXN4 reported\",\n      \"pmids\": [\"40542427\"],\n      \"is_preprint\": false\n    }\n  ],\n  \"current_model\": \"SFXN4 is a five-transmembrane inner mitochondrial membrane protein that functions as a complex I assembly factor by interacting with the MCIA complex and facilitating assembly of the ND2 module; it is also essential for Fe-S cluster biogenesis, mitochondrial iron homeostasis, and respiratory chain function, with loss-of-function causing complex I deficiency, impaired Fe-S cluster formation, iron redistribution to mitochondria, and defects in heme synthesis (reduced ferrochelatase and ALAS2 translation), collectively explaining why SFXN4 mutations cause mitochondrial disease with macrocytic anemia.\"\n}\n```","stage2_raw":"{\n  \"mechanistic_narrative\": \"SFXN4 is a mitochondrial inner membrane protein essential for respiratory chain function and erythropoiesis, with loss-of-function mutations causing mitochondrial disease accompanied by macrocytic anemia [#0]. Mechanistically, SFXN4 acts as a complex I assembly factor: it interacts with the MCIA (Mitochondrial Complex I Assembly) complex and is specifically required for assembly of the ND2 module, such that its loss produces complex I enzyme deficiency and depletion of complex I subunit proteins [#2, #4]. SFXN4 is independently required for iron-sulfur (Fe-S) cluster biogenesis, and its loss diminishes respiratory chain complex stability, shifts metabolism toward glycolysis, perturbs the cytosolic aconitase-IRP1 switch, redistributes iron from cytosol to mitochondria, and impairs heme synthesis through reduced ferrochelatase levels and inhibited ALAS2 translation — connecting its molecular activity to the anemia phenotype [#1]. Disruption of Fe-S-dependent processes downstream of SFXN4 loss extends to DNA repair enzymes, and SFXN4 depletion sensitizes ovarian cancer cells to DNA-damaging agents and PARP inhibitors while restraining tumor growth in xenografts [#3].\",\n  \"teleology\": [\n    {\n      \"year\": 2013,\n      \"claim\": \"Established SFXN4 as a disease gene by linking its loss to mitochondrial respiratory failure and macrocytic anemia, framing it as a respiratory homeostasis factor rather than a bystander locus.\",\n      \"evidence\": \"Exome sequencing of affected individuals with reciprocal in vitro and in vivo complementation and zebrafish morpholino knockdown\",\n      \"pmids\": [\"24119684\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\n        \"No molecular mechanism for how SFXN4 supports respiration identified\",\n        \"Connection between respiratory defect and anemia not resolved at this stage\"\n      ]\n    },\n    {\n      \"year\": 2019,\n      \"claim\": \"Placed SFXN4 upstream of Fe-S cluster biogenesis and iron/heme handling, explaining how its loss could simultaneously cripple respiration and erythropoiesis.\",\n      \"evidence\": \"SFXN4 knockout cell lines with Fe-S activity assays, metabolic flux analysis, and ferrochelatase/ALAS2 readouts; plus a patient muscle study with biochemical and ultrastructural complex I deficiency\",\n      \"pmids\": [\"31873120\", \"31059822\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\n        \"Whether SFXN4 directly catalyzes Fe-S assembly or acts indirectly not distinguished\",\n        \"Mechanism linking SFXN4 to ALAS2 translational control unknown\",\n        \"Patient findings rest on a single case\"\n      ]\n    },\n    {\n      \"year\": 2022,\n      \"claim\": \"Defined a direct molecular role for SFXN4 as a complex I assembly factor acting through the MCIA complex at the ND2 module, providing a concrete mechanism for the complex I deficiency.\",\n      \"evidence\": \"Reciprocal Co-immunoprecipitation, complexome profiling, and SFXN4 KO complex I assembly assays\",\n      \"pmids\": [\"35333655\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\n        \"How a putative transporter contributes to module assembly is unresolved\",\n        \"Relationship between the assembly role and the Fe-S/iron role not reconciled\"\n      ]\n    },\n    {\n      \"year\": 2022,\n      \"claim\": \"Extended the consequences of SFXN4-dependent Fe-S biogenesis to genome maintenance and identified a therapeutic vulnerability in cancer.\",\n      \"evidence\": \"siRNA knockdown and KO with Fe-S/ROS assays, DNA repair and drug-sensitivity assays, and mouse xenograft tumor growth experiments\",\n      \"pmids\": [\"36402786\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\n        \"Which specific Fe-S DNA repair enzymes are rate-limiting not defined\",\n        \"Single-lab findings without independent replication\"\n      ]\n    },\n    {\n      \"year\": null,\n      \"claim\": \"The transport substrate of SFXN4 and how a single protein integrates complex I ND2-module assembly with Fe-S cluster biogenesis and iron homeostasis remain unresolved.\",\n      \"evidence\": \"\",\n      \"pmids\": [],\n      \"confidence\": \"Low\",\n      \"gaps\": [\n        \"No demonstrated transported substrate for SFXN4\",\n        \"No structural model of SFXN4 within the MCIA complex\",\n        \"Mechanistic link between assembly function and iron/Fe-S function not established\"\n      ]\n    }\n  ],\n  \"mechanism_profile\": {\n    \"molecular_activity\": [\n      {\"term_id\": \"GO:0005215\", \"supporting_discovery_ids\": [5, 7]}\n    ],\n    \"localization\": [\n      {\"term_id\": \"GO:0005739\", \"supporting_discovery_ids\": [0, 5]}\n    ],\n    \"pathway\": [\n      {\"term_id\": \"R-HSA-1430728\", \"supporting_discovery_ids\": [1, 2]},\n      {\"term_id\": \"R-HSA-1852241\", \"supporting_discovery_ids\": [2]}\n    ],\n    \"complexes\": [\"MCIA complex\"],\n    \"partners\": [],\n    \"other_free_text\": []\n  }\n}","audit_flag":null,"evaluation":{"pairwise":"win","faith_supported":4,"faith_total":4,"faith_pct":100.0}}