Alcohol dependence was the first behavioral disorder to have validated genetic findings. In 1972, subjects of Asian descent were noted to have facial flushing and decreased alcohol tolerance compared with subjects of European origin.10 This was hypothesized to be genetic rather than cultural, based on observations that infants of Asian descent who were exposed to a small amount of alcohol were more likely to flush than infants of European descent.10 The flushing reaction to ingestion of alcohol was found to be secondary to a deficiency of aldehyde dehydrogenase (specifically ALDH2), an enzyme involved in the metabolism of ethanol.11 The prevalence of ALDH2 deficiency was then examined in the Japanese population and found to be 41% in the general population and 2% in alcoholics, suggesting a protective role for the deficiency of ALDH2 in alcoholism.12
