Age of alcohol initiation and personality disorders as predictors of alcohol problems in early adulthood: A twin study

Background: Research indicates that early alcohol initiation results in an increased risk for later alcoholism. It is, however, not known whether early alcohol exposure is a causal factor for alcoholism, or if early alcohol initiation indicates a genetic predisposition for alcoholism, as well as other behavior and substance use problems. Two forms of alcoholism have been postulated; an early onset type associated with disinhibited behavior, and a late onset type associated with anxiety. Objective: We aim to study the genetic and environmental contribution to the development of binge drinking during early adulthood. Furthermore, we aim to examine if there is a direct effect of early alcohol initiation on binge drinking, cannabis use and alcoholism, or if these relations are explained by common genetic and environmental factors. We seek to identify common and unique genetic and environmental risk factors for DSM-IV externalizing personality disorders (PDs) and early alcohol initiation on one side, and inte rnalizing PDs and late initiation on the other side. Lastly, we aim to estimate to what extent the etiological factors influencing cannabis use and alcoholism are the same as those for DSM-IV PDs. Method: 2,801 twins have been examined with structured ps ychiatric interviews measuring DSM-IV axis I and axis II diagnoses. Both epidemiological statistical analyses and uni- or multivariate twin models will be used. Scientific importance: This study will increase our knowledge of alcoholism, cannabis use and the relating psychiatric comorbidity in the Norwegian population. The results will provide new insight on whether early alcohol initiation is best viewed as a direct causal factor for cannabis use and alcoholism. Furthermore, the results will contribute to the understanding of common genetic and environmental factors influencing variation in age of alcohol initiation, alcoholism, cannabis use and PDs.