Allele frequencies of thiopurine S-methyltransferase (TPMT) variants in the Nigerian population

Introduction Thiopurine S-methyltransferase (TPMT) methylates clinically relevant thiopurine drugs most of which are noted for adverse reactions in certain users, largely due to polymorphisms in the TPMT gene. Aim This study investigated the prevalence of functionally relevant TPMT alleles in the Nigerian population. Material and methods One hundred eighty unrelated subjects consisting of 123 males and 57 females from the main Nigerian ethnicities (44 Igbo, 101 Yoruba, 23 Hausa and 12 from other minor ethnic groups) were genotyped for TPMT*2, *3B, *3C and *4 alleles using the iPLEX genotyping assay technique. The genotype calls were validated with Sanger sequencing in a random set of samples and the acquired data were assessed for Hardy–Weinberg equilibrium using the Fisher's exact test. Results and discussion Defective TMPT alleles were found in individuals representing 10% of the study population. TPMT*3C constituted 9.4% (95% CI, 5.6–14.7) of all alleles detected, with one homozygote and 17 heterozygotes recorded. The prevalence of the TPMT*3C allele in the population conformed with Hardy–Weinberg equilibrium. TPMT*2, 3B and *4 were, however, not detected in the population. Conclusions TPMT*3C was the only defective allele identified in Nigerians and may hence be the major underlying genetic contributor to adverse reactions due to thiopurine drugs in the population.