Reduced activity of a thermolabile form of methylenetetrahydrofolate reductase, caused by a C677T polymorphism in the MTHFR gene (rs1801133, alanine to valine amino-acid change), is the most common genetic factor for moderate hyperhomocysteinemia, and a higher prevalence of C677T has been found in patients with POAG [18]. This evidence concerns the gene MTHFR and open-angle glaucoma.