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