TPMT*43 is assigned no function based on limited evidence. TPMT*43 results in a splicing defect and the loss of exon 5, producing a non-functional enzyme (31005613, 32865889). Erythrocytes from an individual genotyped TPMT*1/*43 exhibited intermediate enzymatic activity (31005613, 32865889). Ten out of ten variant effect predictors tested by CPIC staff predict that the TPMT*43-defining SNVs, c.234G>T (p.W78C) and c.262G>A (p.G88S), impair protein function.