Comparative genotype and allele frequency analysis of CYP1A1 polymorphisms (rs4646903 and rs1048943) in Bangladeshi shipyard workers with occupational heavy metal exposure

Abstract

Workers in the ship-breaking and metal-scrapping yards of Bangladesh are chronically exposed to a mixture of heavy metals that includes the Group 1 human carcinogens arsenic, cadmium, and chromium. Susceptibility to the genotoxic consequences of such exposure is modulated by inherited variation in xenobiotic-metabolizing enzyme genes, among which CYP1A1 is central: it is induced through the aryl hydrocarbon receptor by both polycyclic aromatic hydrocarbons and several of these metals, and it bioactivates pro-carcinogens into DNA-reactive intermediates. The study determined and compared the first CYP1A1 genotype and allele frequency data for a Bangladeshi ship-breaking and metal-scrapping workforce. Allele frequencies of two functional CYP1A1 polymorphisms, rs4646903 and rs1048943, were compared between 55 workers with ten years of occupational heavy metal exposure and 55 healthy unexposed controls. Genomic DNA was extracted from peripheral blood by spin column and genotyped by two-tube allele-specific Amplification Refractory Mutation System PCR (ARMS-PCR) with agarose gel electrophoresis, using two allele-specific forward primers and one common reverse primer per locus. Allele distributions were compared by chi-square, and the association between genotype and group membership was estimated by multivariable logistic regression adjusted for age and sex under codominant, dominant, recessive, over-dominant, and additive models. Allele distributions differed significantly between the two groups at both loci (rs4646903: OR 0.492, 95% CI 0.282-0.859, P = 0.0121; rs1048943: OR 0.446, 95% CI 0.253-0.786, P = 0.0048). At rs4646903 the G-containing genotypes were associated with higher odds of worker status (additive OR 2.855, P = 0.0048), whereas at rs1048943 the C-containing genotypes were associated with lower odds (additive OR 0.302, P = 0.0037). No worker carried the rs1048943 CC genotype, rendering the recessive and CC-versus-TT contrasts inestimable. Age, but not sex, was an independent predictor of group membership in every model. Because both polymorphisms are germline variants that cannot be induced by adult exposure, and because no clinical outcome was measured, these findings are interpreted as associations with exposure-group membership within this sample.