Pharmacogenomics of alcohol response and addiction

Alcoholism is a complex psychiatric disorder that has high heritability (50-60%) and is relatively common; in the US the lifetime prevalence of alcohol dependence is 20% in men and 8% in women. Current psychosocial and pharmacological therapies have relatively modest effects. Treatment is complicated by the fact that alcoholism is often co-morbid with other disorders, including anxiety, depression, and antisocial personality disorder. Approximately 80% of alcoholics smoke cigarettes and there is considerable genetic overlap between nicotine and alcohol addiction. Convergent evidence supports the classification of alcoholics into two broad categories: type 1 - later onset with feelings of anxiety, guilt, and high harm avoidance; and type 2 - early age of onset, usually men, impulsive, antisocial, and with low levels of brain serotonin. The pharmacogenomics of alcohol response is well established; genetic variants for the principal enzymes of alcohol metabolism influence drinking behavior and protect against alcoholism. Vulnerability to alcoholism is likely to be due to multiple interacting genetic loci of small to modest effects. First-line therapeutic targets for alcoholism are neurotransmitter pathway genes implicated in alcohol use. Of particular interest are the 'reward pathway' (serotonin, dopamine, GABA, glutamate, and beta endorphin) and the behavioral stress response system (corticotrophin-releasing factor and neuropeptide Y). Common functional polymorphisms in these genes are likely to be predictive (although each with small effect) of individualized pharmacological responses. Genetic studies, including case-control association studies and genome wide linkage studies, have identified associations between alcoholism and common functional polymorphisms in several candidate genes. Meanwhile, the current pharmacological therapies for alcoholism are effective in some alcoholics but not all. Some progress has been made in elucidating the pharmacogenomic responses to these drugs, particularly in the context of the type 1/type 2 classification system for alcoholics.