The association of rs1801133 with MS was uncovered in the combined analysis of the three Nordic sample sets and is a missense variant is in exon 5 of the MTHFR gene, encoding 5,10-methylenetetrahydrofolate reductase, a key enzyme in the intracellular folate (vitamin B9) metabolism and homeostasis. The gene discussed is MTHFR; the disease is myeloid sarcoma.