Thiopurine S-methyltransferase genetic polymorphism in the Thai population

Aims To determine the incidence of the thiopurine S-methyltransferase (TPMT) genetic polymorphism in the Thai population. Methods Genomic DNAs were isolated from peripheral blood leucocytes of 200 healthy Thais. The frequencies of five allelic variants of the TPMT gene, TPMT*2, *3A, *3B, *3C and *6 were determined using allele specific polymerase chain reaction (PCR) or PCR-Restriction fragment length polymorphism technique. Results Of the 200 Thai subjects participating in this study, 181 subjects (90.5%) were homozygous for TPMT*1, 18 subjects (9.0%) were heterozygous for TPMT*1/*3C. Only one subject (0.5%) was homozygous for TPMT*3C. The frequency of TPMT*3C mutant allele was 0.050. Conclusions Although the TPMT*3C is the most prevalent mutant allele in Asian populations, the frequency of this defective allele is significantly higher in Thais than has been reported in other Asian populations.