TPMT*14 is assigned no function based on moderate evidence. Erythrocytes from individuals genotyped TPMT*3A/*14 and TPMT*1/*14 exhibited very low and intermediate enzymatic activity, respectively (15083071, 31005613). An in vitro study using a mammalian cell expression system found that TPMT.14 protein expression and enzymatic activity are undetectable in cells (18708949). Four out of eight variant effect predictors tested by CPIC staff predict that the TPMT*14-defining SNV, c.1A>G (p.M1V), impairs protein function. c.1A>G (p.M1V) is predicted to disrupt protein translation due to the loss of the canonical start codon, and there is no alternative start codon available