MTHFR and acute lymphoblastic leukemia: The large interindividual variability in RBC folate levels in our pediatric ALL patients are in line with the variability reported in the healthy population and may be partly explained by small differences in pre-analytical conditions, genetic variation in genes of folate transporters and metabolizing enzymes, such as the MTHFR c.677 C > T genotype, as well as differences in dietary folate intake and supplementation [22].