Subgroup analyses by leukemia types again demonstrated the protective role of MTHFR 677 TT polymorphism against ALL in American children (RR = 0.71, 95% CI [.51, 0.99], p = .0405) while MTHFR 677 CC and CT genotypes increased risk of ALL in American children (RR = 1.05, 95% CI [1.00, 1.09], p = .0388). This evidence concerns the gene MTHFR and acute lymphoblastic leukemia.