Aims To determine the frequencies of four thiopurine S-methyltransferase (TPMT) mutant alleles, TPMT*2, *3A, *3B and *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*3C heterozygote was identified (gene frequency 0.3%). TPMT*2,*3A and *3B were not detected. In addition, TPMT*3C was found to have been inherited from the mother and passed on to the son of the propositus.
Conclusions TPMT*3C 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.