The TPMT*6 allele has been assigned as a no function allele by the DPWG. Patients with the *6 allele in combination with a normal function allele may have an increased likelihood of toxicity when treated with mercaptopurine as compared to patients with two normal function alleles. However, conflicting evidence has been reported. Note that CPIC assigned TPMT*6 as an uncertain function allele. Other genetic and clinical factors may also influence mercaptopurine toxicity.