TPMT*4 is assigned no function based on strong evidence. The SNV characteristic of TPMT*4 (c.626-1G>A) is located in the splice junction between intron 9 and exon 10 and disrupts the canonical splice site, resulting in production of a truncated protein. Erythrocytes from individuals heterozygous for TPMT*4 exhibited intermediate TPMT enzymatic activity (9486974, 12880540), while erythrocytes from individuals carrying TPMT*4 in combination with another no function allele had very low TPMT enzymatic activity (9246020, 9486974). The in silico variant effect predictors, CADD and PhD-SNPg, predict that the TPMT*4-deifning SNV, c. 626-1G>A, impairs protein function. Additionally, c.626-1G>A is predicted to result in the loss of the acceptor splice site by SpliceAI.