The most significant PACSIN2 SNP in the HapMap analysis for TPMT activity, rs2413739, was also significantly associated with TPMT activity in patients with ALL, independently from TPMT genotype: the CC genotype for the rs2413739 SNP displayed a higher TPMT activity in comparison to the TT genotype. Here, TPMT is linked to acute lymphoblastic leukemia.