MTHFR and acute lymphoblastic leukemia: Most of these studies indicated that the MTHFR C677T gene polymorphism causes oral mucositis, myelosuppressive effects, and liver, intestinal, and skin toxicities, and also leads to an increased relapse rate in children with ALL [6,7,8,9,10,11,12,13,14,15,16,17,18,19,22].