TPMT*2 is assigned no function based on definitive evidence. Erythrocytes from individuals heterozygous for TPMT*2 exhibited intermediate enzymatic activity, while erythrocytes from individuals homozygous for TPMT*2 or heterozygous for TPMT*2 in combination with another no function allele exhibited low enzymatic activity (7862671, 9246020, 9695718, 15226673, 23252716, 31005613, 12880540, 14508387, 14656901, 9103127, 11372592, 18021342, 9831928, 14985890). Patients carrying TPMT*2 alleles exhibited increased plasma concentrations of TGNs, decreased plasma concentrations of methylated metabolites, and tolerated lower doses of thiopurines (19057372, 18021342, 10580024). In vitro studies found that TPMT.2 protein expression and enzymatic activity was decreased by 75-100% relative to TPMT*1 in yeast (7862671, 9177237) and mammalian cells (16220112, 9177237, 18708949), as well as patient erythrocytes (9177237, 9695718). TPMT.2 decreased protein expression has been attributed to rapid degradation by the proteasome (9177237, 16220112). Ten out of ten variant effect predictors tested by CPIC staff predict that the TPMT*2-defining SNV, c.238G>C (p.A80P), impairs protein function.