TPMT*34 is assigned no function based on moderate evidence. Erythrocytes from individuals genotyped TPMT*1/*34 exhibited intermediate activity (23252716, 33118454). One of these patients received 44 mg/m2 thioguanine and exhibited a plasma TGN concentration of 3006 pmol/8×108 RBCs (23252716). Seven out of ten variant effect predictors tested by CPIC staff predict that the TPMT*34-defining SNV, c.244C>T (p.R82W), impairs protein function.