MTHFR and stroke disorder: Previous Mendelian randomization studies involving homocysteine metabolism concluded that people who were homozygous for the wild-type allele (CC) of the MTHFR gene, compared to homozygous for the mutant allele (TT), had 1.93-2.7mol/L [6-7] or 25% higher homocysteine concentrations [6-8], a 26% higher risk of stroke [6-8], and a 16% higher risk of coronary heart disease (CHD) [7]. Homocysteine can build up in the arteries, which may increase the risk of blood clots, heart attack, and stroke.