The genetic basis of addiction and relevant cellular mechanisms.

Classical genetic research approaches to determining the genetic contribution to a multifactorial condition have been used to quantify the proportion of addiction and substance abuse that is a result of heritable genetic factors versus environmental factors. Family studies, twin studies, and adoption studies have all been applied for individuals and families with a history of addiction and substance dependence. As a whole these studies estimate that there is a 40% to 60% heritability for addiction and alcoholism. Family studies are used to assess the heritability of addiction by examining the risk of addiction in relatives of a known affected individual. Studies of alcoholism and other drugs have showed that first-degree relatives of individuals with addiction are at an increased risk to develop an addiction problem, compared with individuals without a family history. Family studies are often limited in the ability to exclude common environment factors shared in families such as living environment, socioeconomic status, and stressor events. Adoption studies serve as a tool to limit the shared environmental factors that arise in family studies by investigating individuals raised by nonrelated adoptive parents. Numerous studies of alcoholism have suggested that children with a biological family history of alcoholism raised by nonalcoholic parents are at an increased risk for developing