Thiopurine S-methyltransferase (TPMT) catalyses the S-methylation of thiopurine drugs. In Caucasians, four variant TPMT alleles have been detected in over 80% of individuals with low or intermediate TPMT activity. The wild-type allele is designated as TPMT*1 and the mutant alleles are designated TPMT*2 through TPMT*8. The frequency of these alleles in different ethnic groups has not been well defined. In this study, one hundred individuals, from each of the Indonesian, Thai and Philippine populations, together with 249 Taiwanese, were analysed by polymerase chain reaction-restriction fragment length polymorphism and direct sequencing methods. The results showed that the allelic frequencies of TPMT*3C were 0.6% for Taiwanese and 1% for Filipino, Thai and Indonesian populations, respectively. One Filipino with a Caucasian parent was found to be heterozygous for the TPMT*2 allele. This study provides the first analysis of the allele frequency distribution of all known TPMT mutations in South-east Asian populations.
