Genetic Polymorphisms In Alcohol And Xenobiotic Metabolizing Enzymes As Risk Factors Of Oesophageal Cancer In Sudan

Abstract

Genetic differences in sensitivity to environmental carcinogens are the most important factors in the estimate risk of human cancer. Individual susceptibility to oesophageal cancer may be partly due to genetic differences in genes controlling the metabolic balance between the oxidation (activation) and conjugation (detoxification) of procarcinogens. The objectives of this prospective case-control study were to investigate genetic differences among Sudanese patients with oesophageal cancer in comparison with healthy controls using single nucleotide polymorphisms (SNPs) as genetic markers and polymerase chain reaction based restriction fragment length polymorphism as genotyping method and to correlate between those polymorphisms and the risk of oesophageal cancer in Sudan. Alcohol-metabolizing genes (ADH and ALDH2) and xenobiotic-metabolizing genes (CYP3A5, GSTM1, GSTT1 and SULT1A1) have been studied for this purpose. One hundred and thirty four (134) oesophageal cancer patients who underwent oesophagoscopy at the National Centre of Gastrointestinal and Liver Diseases, Ibn Sina Hospital and Khartoum Teaching Hospital and 233 healthy Sudanese volunteers were studied during the period (2001-2005). Blood samples were collected from all subjects in EDTA coated tubes. Genomic DNA was isolated and assessed for genetiC variations using eight differEnt polymorphic loci of the respective genes. Eight primer pairs were designed according to published sequence data for exon 3 and exon 9 in ADH2, exon 8 in ADH3, exon12 in ALDH2, intron 3 in CYP3A5, exon 7 in SULT1A1 and in the regions containing the d%letion in both GSTTM1 and GSTT1 genes. DNA was amplified using polymerase chain reaction and the PCR products were inves4igated for SNP, using RFLP procedures. The different genotypes were scored for each locus and data were analyzed using computer software SPSS for Windows. Allelic frequencies for each gene in patients and controls were computed using the genotype data and the results were used for further analysis. The odd-ratios were estimated by the logistic regression model, assuming 95% as the confidence interval (CI). All loci were polymorphic and two alleles per locus were detected. Our findings showed that there are no significant differences in the frequency distribution of ADH2, ALDH2, CYP3A5 and SULT1A1 Alleles between oesophageal cancer p`tients and healthy controls (P>0.05). The study did indicate a significant VI difference in GSTM1 and GSTT1 null-genotypes between patients and controls (P<0.05). In conclusion, our results cnnfirmed the usefulness of SNPs for research on genetic variations and relationships to cancer suscepTibility. The present study showed for the first time the alleLic frequencies of ADH, ALDH2, CYP3A5, GSTM1, GSTT1 and SUL1A1 in Sudanese populations. Key words: Oesophageal cancer, Genetic polymorphism, SNPs, PCR-RFLP, Alcoholmetabolizing enzymes, Xenobiotic-metabolizing enzymes.