The most often studied genetic variant, showing the strongest association with increased tHcy, is the cytosine (C) to thymine (T) substitution at position 677 of the methylene tetrahydrofolate reductase (MTHFR) gene (rs1801133).12–14 Case–control studies that investigated the association of the MTHFR C677T variant with stroke yielded inconsistent results, which is likely because of small sample sizes and the varying stroke phenotypes studied. This evidence concerns the gene MTHFR and Stroke.