MTHFR and homocystinuria: In this study, we identified a novel gene variant of c.602 A > C (p.His201Pro) in the family with homocystinuria due to MTHFR deficiency, which results in a missense mutation on exon 5 of the MTHFR gene, and the 201 His is one of the FAD-binding sites of the MTHFR protein.