Subgroup analyses by regions showed that MTHFR 677 polymorphisms were protective against leukemia in children from Europe, East Asia, and America (Europe–CT type: RR = 0.94, 95% CI [0.89, 0.99], p = .0316; TT+CT types: RR = 0.94, 95% CI [0.90, 0.99], p = .0187; East Asia–CT type: RR = 0.93, 95% CI [0.86, 1.00], p = .0491; America – TT type: RR = 0.70, 95% CI [0.52, 0.95], p = .0212; TT+CT types: RR = 0.83, 95% CI [0.68, 0.99], p = .0449) (Table 1A, Table 2). This evidence concerns the gene MTHFR and leukemia.