Genetic analysis of thiopurine methyltransferase polymorphism in a Japanese population

Thiopurine methyltransferase (TPMT) catalyses the S-methylation of thiopurine drugs such as 6-mercaptopurine, 6-thioguanine, and azathiopurine. Several mutations in the TPMT gene have been identified which correlate with a low activity phenotype. The molecular basis for the genetic polymorphism of TPMT has been established for European Caucasians, African-Americans, Southwest Asians and Chinese, but it remains to be elucidated in Japanese populations. The frequency of the four allelic variants of the TPMT gene, TPMT* 2 (G238C), TPMT* 3A (G460A and A719G), TPMT* 3B (G460A) and TPMT* 3C (A719G) were determined in Japanese samples (n = 192) using polymerase chain reaction (PCR)-RFLP and allele-specific PCR-based assays. TPMT* 3C was found in 0.8% of the samples (three heterozygotes). The TPMT* 2, TPMT* 3A and TPMT* 3B alleles were not detected in any of the samples analyzed. This study provides the first analysis of TPMT mutant allele frequency in a sample of Japanese population and indicates that TPMT* 3C is the most common allele in Japanese subjects. (C) 2000 Published by Elsevier Science B.V.