Background: Human mitochondrial aldehyde dehydrogenase (ALDH2) is a major enzyme responsible for the oxidation of acetaldehyde derived from ethanol metabolism. The human ALDH2 gene shows genetic polymorphism at position 1510 with a G to A transition in exon 12. This mutation leads to ALDH2 enzyme deficiency and protection against alcoholism. As yet, no polymorphism for the promoter region of the ALDH2 gene has been reported.
Methods: We analyzed 600 nucleotides of the promoter region in addition to exon 12 from 571 Japanese, 68 Chinese, 80 Myanmar, 60 Mongolians, and 82 North-American Caucasians using single-strand conformational change polymorphism (SSCP) analysis and the polymerase chain reaction (PCR). PCR products that showed an aberrant banding pattern detected by the SSCP analysis were subjected to PCR direct sequencing.
Results: A novel polymorphism at -357 with a G to A substitution was found in all the population groups, including North-American Caucasians. In addition, the polymorphic status in the promoter and exon 12 suggested linkage disequilibrium between the two loci, which indicated that among Japanese, the ALDH2*2 allele is linked to the G promoter allele, and theALDH2*1 allele is linked to the A allele. A total of 206 healthy male controls and 185 alcoholic male patients with the homozygous ALDH2*1 genotype were analyzed for the polymorphism in the promoter. Genotypic frequencies of GG, GA, and AA for alcoholics were 54.1%, 44.3%, and 1.6%, and those for controls were 52.9%, 40.3%, and 6.8%, respectively. The A allele frequencies for alcoholics and controls were 0.24 and 0.27, respectively. A chi2 test for the entire 3 x 2 table indicated significant variations in the three genotypes (chi2 = 6.40, p < 0.05). However, no significant difference in allelic frequencies between the two groups was observed.
Conclusion: This new polymorphism in the ALDH2 promoter is present in all populations studied. Further analysis in other ethnic groups is necessary to establish this as an additional risk factor for alcoholism.