Relationship between metabolic phenotypes and genotypes of CYP1A2 and CYP2A6 in the Nigerian population

CYP1A2 and CYP2A6 are polymorphic drug-metabolising enzymes that are also implicated in the activation of procarcinogens in humans. Some of their alleles and haplotypes, often varied in prevalence across populations, are thought to influence activity despite the known contribution of environmental factors. This study assessed the potential influence of some genetic variants of CYP1A2 and CYP2A6 on metabolic phenotypes in Nigerians. Genomic DNA was extracted from blood samples of 100 healthy, unrelated subjects for whom CYP1A2 and CYP2A6 phenotypes had previously been determined, alongside an additional 80 other individuals for whom phenotype data were unavailable. The samples were screened for CYP1A2 (∗1C,∗1D,∗1E,∗1F, ∗3,∗4,∗6,∗7) and CYP2A6 (∗9,∗11,∗17) alleles using the Sequenom MassARRAY platform for some alleles and direct Sanger sequencing for others. The genetic data acquired were subsequently analysed for haplotypes and assessed for concordance with phenotypes. All five CYP1A2 haplotypes (CYP1A2∗1F, 1J, 1N, 1L, 1W) identified in the Nigerian population were not significantly predictive of metabolic phenotypes. Heterozygous CYP1A2∗1J carriers and homozygous CYP1A2∗1W carriers showed statistically insignificant decrease in CYP1A2 activity. The CYP2A6∗9/∗17 genotype was, however, significantly associated with the CYP2A6-poor metabolic phenotype, whereas CYP2A6∗9 or CYP2A6∗17 alone did not show any such association. CYP2A6∗11 was not detected in the population. Our findings suggest that CYP1A2 alleles or haplotypes were not predictive of metabolic phenotypes in the Nigerian population. Carriers of CYP2A6∗9/∗17 genotype are likely to be poor metabolisers of CYP2A6 substrates and may experience adverse reactions or poor efficacy while using drugs metabolised mainly by CYP2A6.