Two SNPs in the ITPA gene, namely a non-synonymous C94A transition and the intronic IVS2+21A>C variant, with a frequency of approximately 6% and 13%, respectively, in Caucasians [25], have been correlated with defective enzyme activity [14], [26] leading to a higher risk of myelotoxicity and hepatotoxicity in pediatric ALL patients [7], [22], [27]. The gene discussed is ITPA; the disease is acute lymphoblastic leukemia.