Interestingly, in the discovery cohort, the effects of TPMT, SLCO1B1 and PACSIN2 polymorphisms were independent from each other, both in a multivariate logistic regression model and in a classification and regression tree analysis and could be combined in a multilocus genotype of potential importance to predict the incidence of severe mucositis in children with ALL treated with consolidation therapy comprising the combination of methotrexate and mercaptopurine (Figure 1). The gene discussed is PACSIN2; the disease is acute lymphoblastic leukemia.