{"variant":{"rsid":"rs1801133","gene":"MTHFR","name":"C677T (Ala222Val, exon 4)","alleles":"C>T. CC = wild type, CT = heterozygous, TT = homozygous variant. Some platforms report the minus strand (G/A); interpret G/A as C/T.","effect":"Reduces enzyme thermostability. TT homozygotes have ~30% of normal MTHFR activity; CT heterozygotes ~65%. ClinVar: risk factor with variable penetrance for hyperhomocysteinemia, not a pathogenic disease variant.","frequency_note":"T allele ~30% in Europeans, ~50% in Mexican populations, ~10% in sub-Saharan Africans. Companion blog: TT ~8–12% of Europeans (other blog posts say 10–15%; see INVENTARIO).","sources":[{"label":"ClinVar — MTHFR gene entries","url":"https://www.ncbi.nlm.nih.gov/clinvar/?term=MTHFR%5Bgene%5D"},{"label":"Frosst et al., Nat Genet 1995","url":null}]},"gene":{"symbol":"MTHFR","name":"5,10-Methylenetetrahydrofolate reductase","url":"https://deepdna.ai/api/v1/genes/MTHFR"},"meta":{"disclaimer":"Educational information only, not medical advice or diagnosis. Consult a clinician before acting on genetic information.","api_version":"2026-09-20","docs":"https://deepdna.ai/docs/","status":"live"}}