The regulation of homocysteine requires several co-factors (including folic acid, vitamin-B6 and B12) and enzymes, such as methionine synthase (MS), methylenetetrahydrofolate reductase (MTHFR), and cystathionine beta-synthase (CBS).6 Vitamin-B12 and folic acid are essential for cell metabolism and any deficiency of these vitamins may cause interference in DNA synthesis and homocysteine metabolism.6,7 Disturbances in any step of the homocysteine metabolic pathway, caused by either vitamin deficiencies or enzymatic errors, can result in the accumulation of plasma homocysteine. The gene discussed is MTR; the disease is vitamin deficiency.