DHFR and acute lymphoblastic leukemia: Interestingly, DHFR DD-homozygous children belonging to the whole cohort (n = 235) showed a significant delay in ALL onset (7.5 ± 4.8 years; P = 0.002) when compared to WW-homozygotes (5.2 ± 3.7 years), while WD-heterozygotes showed intermediate mean age (6.7 ± 4.4 years).