Polymorphism of the rat liver mitochondrial aldehyde dehydrogenase cDNA

In humans, a deficiency in mitochondrial aldehyde dehydrogenase (Class 2 ALDH) activity due to a single base-pair exchange in its structural gene serves as a deterrent to excessive alcohol consumption. Differences in Class 2 ALDH isozyme patterns on isoelectric focusing gels have been observed in the selectively bred, alcohol-preferring (P) and alcohol-nonpreferring (NP) lines of rats. To determine whether the differences are the result of sequence variation in the structural gene, we sequenced the cDNAs for Class 2 ALDH from P and NP rats. A synonymous exchange was seen in the codon for amino acid 473 in both lines, when compared with published sequences. Additionally, when the cDNA from P rats was used as reference, a substitution (G for A) was identified in the cDNA of NP rats which changes amino acid 67 from Gln (CAG codon; ALDH2Q allele) to Arg (CGG codon; ALDH2R allele). The Arg for Gln substitution makes the enzyme more basic and could account for the different electrophoretic mobilities. To determine whether the polymorphism was associated with drinking behavior, we genotyped the ALDH2 locus by amplifying rat genomic DNA encompassing the nucleotide exchange followed by probing with allele-specific oligonucleotides. There are highly significant differences in the frequencies of the two alleles in the P and NP rat lines. The frequency of the ALDH2R allele is 63% in the NP line and only 18% in the P line, whereas the frequency of the ALDH2Q allele is 82% in the P line and 37% in the NP line.