[25] The large interindividual variability in intracellular erythrocyte folate levels in our pediatric ALL patients are in line with the variability reported in the healthy population and might be partly explained by 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. The gene discussed is MTHFR; the disease is acute lymphoblastic leukemia.