TPMT*30 is assigned uncertain function based on inadequate evidence. An in vitro study using a mammalian cell expression system found that TPMT.30 exhibited decreased affinity for 6-TG and 90% decreased enzymatic activity relative to TPMT.1 (18708949). One out of ten variant effect predictors tested by CPIC staff predicts that the TPMT*30-defining SNV, c.106G>A (p.G36S), impairs protein function. Of note, TPMT*30 was originally designated TPMT*24 (23407052).