NUDT15*19 is assigned no function based on limited evidence. One patient genotyped NUDT15*1/*19 received 150 mg of azathiopurine daily and experienced pancytopenia after 1 week of treatment. However, this patient was also heterozygous for an inactivating TPMT allele (30728528). Four out of seven variant effect predictors tested by CPIC staff predict that the NUDT15*19-defining SNV (c.3G>C (p.M1I)) impairs protein function. c.3G>C is predicted to disrupt protein translation due to the loss of the canonical start codon, and there is no alternative start codon available.