TPMT*33 is assigned no function based on limited evidence. Erythrocytes from an individual genotyped TPMT*1/*33 exhibited intermediate enzymatic activity and their 6-TGN plasma concentration was 634 pmol/8×108 RBCs after receiving 54 mg/m2 6-MP (23252716). Erythrocytes from individuals genotyped TPMT*8/*33 exhibited intermediate activity (33118454), however the phase was not determined, and it is possible that these individuals are TPMT*1/*46. Eight out of ten variant effect predictors tested by CPIC staff predict that the TPMT*33-defining SNV, c.487C>T (p.R163C), impairs protein function.