Allelic variants of the thiopurine methyltransferase (TPMT) gene in the Colombian population

Thiopurine methyltransferase (TPMT) catalyzes the inactivation of thiopurine drugs (mercaptopurine, thioguanine and azathioprine) used to treat acute lymphoblastic leukemia, autoimmune diseases and recipients of transplanted organs. No endogenous substrates for this enzyme are known. The TPMT polymorphism is a major determinant of individual differences in the toxicity or therapeutic efficacy of these drugs. The molecular basis of this polymorphism has been established in Caucasians, Africans, African-Americans and Asians, but not yet in the heterogeneous Latin American groups, including the Colombian population. 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 140 Colombian volunteers of Mestizo origin, using allele-specific PCR and PCR-RFLP assays. The *3A allele was found in 10 samples and the *2 allele in one, all heterozygotes; neither homozygous mutant genotypes nor the *3B and *3C alleles were detected. In agreement with these results, 92.1% and 7.9% of the Colombian population correspond to the phenotypes high and intermediate methylators, respectively. These results show that the frequency of mutations and the allelic distribution of the TPMT gene in the Colombian population are similar to the genetic profile found among US and European Caucasian populations, where the *3A allele is prevalent and the *2 allele is currently present.