Frequencies of thiopurine S-methyltransferase mutant alleles (TPMT*2, *3A, *3B and *3C) in 151 healthy Japanese subjects and the inheritance of TPMT*3C in the family of a propositus

Aims To determine the frequencies of four thiopurine S-methyltransferase (TPMT) mutant alleles, TPMT(star)2, (star)3A, (star)3B and (star)3C in a normal Japanese population. Methods Genotypes were determined in 151 Japanese subjects and in six family members of a propositus using polymerase chain reaction (PCR)-restriction fragment length polymorphism and allele-specific PCR assays. Results Only one TPMT(star)3C heterozygote was identified (gene frequency 0.3%). TPMT(star)2, (star)3A and (star)3B were not detected. In addition, TPMT(star)3C was found to have been inherited from the mother and passed on to the son of the propositus. Conclusions (TPMTC)-C-star3 appears to be most prevalent among the known mutant allele of TPMT in a Japanese population which may have some relevance for the treatment of Japanese patients with thiopurine drugs.