The DSM-IV diagnosis of AD requires the manifestation of three or more of the following criteria at any time during the same 12-month period: tolerance, withdrawal, using alcohol more than intended, a persistent desire to cut down or inability to do so, spending a great deal of time obtaining alcohol or recovering from its effects, giving up activities to drink, and continuing alcohol use despite physical or psychological problems (DSM-IV) (AmericanPsychiatricAssociation, 1994). The requirement of any three inherently creates a group of AD individuals that is clinically and likely genetically heterogeneous. Therefore, approaches that focus on potentially more homogeneous subgroups may increase the power to identify novel genetic variants by reducing the clinical (and therefore possibly the genetic) heterogeneity.
