TPMT*45 is assigned no function based on limited evidence. A patient genotyped TPMT*1/*45 exhibited low TPMT enzymatic activity and a plasma 6-TGN concentration above the therapeutic range (33273844). Following reduction of the thiopurine dosage, the patient's 6-TGN plasma concentration decreased and was within the therapeutic range (33273844). However, another patient genotyped TPMT*1/*45 tolerated a 6-MP dose of 73.1 mg/m2 (34412101). TPMT*45 results in the generation of a premature stop codon at residue 226 and the production of a truncated protein. The premature stop occurs upstream of the known "no function" variant (c.719A>G, defining TPMT*3C), suggesting that loss of this region of the protein alters function. Two out of four variant effect predictors tested by CPIC staff predict that the TPMT*45-defining SNV, c.676C>T (p.R226X), impairs protein function. In a study of variant abundance by massively parallel sequencing, the TPMT*45 variant was found to have low protein abundance (29785012).