TPMT*31 is assigned no function based on limited evidence. TPMT.31 exhibited decreased protein expression in patient white blood cells (20881512), and erythrocytes from individuals genotyped TPMT*1/*31 exhibited intermediate enzymatic activity (20881512, 31005613). However, there was no difference in enzymatic activity observed in vitro between recombinant TPMT.1 and TPMT.31 (Vmax=11.1 and 11.8 U/mg, respectively) produced in E coli. (20881512). Five out of ten variant effect predictors tested by CPIC staff predict that the TPMT*31-defining SNV, c.611T>C (p.I204T), impairs protein function. Despite conflicting in vitro evidence, the experts agreed to assign no function based on the available clinical data.