Chapter 2 The Genetic Basis of Addiction

Addiction is a complex disease infl uenced by genetic, environmental, developmental, and social factors. Once viewed as a moral weakness in character, substance use disorders are now defi ned as maladaptive patterns of substance use leading to inability to control use despite signifi cant consequences in the American Psychiatric Association’s Diagnostic and Statistical Manual of Mental Disorders (DSM-IV) [ 1 ] . Family, adoption, and twin studies support the importance of biologic factors and prompted the search for an inherited link. Because addiction is a heterogeneous and complex disorder without a clear Mendelian pattern, identifi cation of specifi c genes has proved challenging. This chapter reviews the role of genetic factors, molecular mechanisms, and related imaging of the addicted brain. Although drug dependency is commonly associated with illegal substances (e.g., opioids, cocaine, marijuana, and methamphetamine), legal substances such as alcohol and nicotine must also be considered. Because there is a preponderance of data on alcohol and tobacco use, these drugs are emphasized throughout the chapter though the concepts are, in many cases, applicable to other substances.