Understanding genetic risk for substance use and addiction: A guide for non-geneticists

There is considerable enthusiasm for the potential of genetics research for prevention and treatment of addiction and other mental disorders. As a result, clinicians are increasingly exposed to issues of genetics that are fairly complex, and for which they may not have been adequately prepared by their training. Studies suggest that the heritability of substance use disorders is approximately 0.5. Others report that family members of affected individuals experience a 4- to 8-fold increased risk of disorder themselves. Statements that addiction is “50% genetic” in origin may be taken by some to imply one's chances of developing the disorder, or that a lack of a positive family history confers immunity. In fact, such conclusions are inaccurate, their implications unwarranted given the true meaning of heritability. Through a review of basic concepts in genetic epidemiology, we attempt to demystify these estimates of risk and situate them within the broader context of addiction. Methods of inferring population genetic variance and individual familial risk are examined, with a focus on their practical application and limitations. An accurate conceptualization of addiction necessitates an approach that transcends specific disciplines, making a basic awareness of the perspectives of disparate specialties key to furthering progress in the field.

► Heritability is the proportion of population variance in a characteristic that is caused by genetic variation.
► Heritability does not represent an individual's risk of disorder.
► An individual's risk of disorder can be estimated from family studies.
► A positive family history is not necessary for disorder development.
► A largely heritable disorder may still be responsive to environmental changes.