MTHFR and myeloid sarcoma: MTHFR is an enzyme involved in the conversion of 5,10-methylenetetrahydrofolate to 5-methyltetrahydrofolate and the missense variant rs1801131 (E429A) has been shown to cause decreased MTHFR enzymatic function and is associated with impaired folate metabolism and mild increases in homocysteine levels (hyperhomocysteinemia) that is reported to occur in MS patients24,25.