Human aldehyde dehydrogenase isozymes and alcohol sensitivity

The metabolism of acetaldehyde has received considerable attention in the past owing to its acute and chronic toxic effects in humans. Two major hepatic ALDH isozymes, ALDH I and ALDH II, differing in their structural and functional properties, have been characterized in humans. ALDH I has a low Km for acetaldehyde and is primarily a mitochondrial enzyme, while ALDH II has a higher Km and is of cytosolic origin. An inherited deficiency of ALDH I isozyme found only among Oriental populations is primarily responsible for producing acute alcohol sensitivity symptoms (flushing response) after consumption of small doses of alcohol. Biochemical, immunochemical, and molecular genetics data indicate a structural mutation in the ALDH I isozyme gene responsible for the loss in catalytic activity. Population genetic studies have revealed the prevalence of ALDH polymorphism among individuals of the Mongoloid race. Flushing response to alcohol is a familial trait, and preliminary family data from Japan, China, and Korea suggest an autosomal codominant inheritance for ALDH I isozyme deficiency. The ALDH polymorphism is apparently responsible for the low incidence of alcoholism in Japanese, Chinese, and Koreans. Alcohol sensitivity due to ALDH I isozyme deficiency may inhibit excessive alcohol drinking.