Aside from elevated Hcy plasma levels found in patients with homocystinuria, various vitamin deficiencies (vitamins B6, B9, and B12), renal failure, hypothyroidism, methylenetetrahydrofolate reductase (MTHFR) deficiency, and diabetes [27], Hcy plasma levels are also associated with physical inactivity, medication, such as anticonvulsant agents, tobacco use, male gender, and age [28]. Here, MTHFR is linked to homocystinuria.