NUDT15*12 is assigned uncertain function based on inadequate evidence. An in vitro study expressed NUDT15*12 in HEK293 cells and found there was no effect on thiopurine sensitivity (32094176). An additional in vitro study found that NUDT15.12 exhibits decreased protein thermostability compared to NUDT15.1 (29519865). Patients carrying the NUDT15*12 allele had a 20% reduction in thiopurine dosing after the occurrence of adverse reactions (29519865). Seven out of nine variant effect predictors tested by CPIC staff predict that the NUDT15*12-defining SNV (c.156C>G (p.F52L)) impairs protein function.