Background: Information on the heritability of the development of alcohol dependence could provide a better understanding of the importance of genetic components in disease transition. Objective: To examine the genetic and nongenetic contributions to the age at onset of regular alcohol use, the age at diagnosis of alcohol dependence, and the transition from regular alcohol use to alcohol dependence. Design: Classic twin study. Setting: General community. Participants: This study included 3372 twin pairs of known zygosity from the Vietnam Era Twin Registry. The diagnosis of DSM-III-R-defined alcohol dependence and related information were obtained through telephone-administered interviews conducted in 1992. Main Outcome Measures: Standardized proportions due to genetic vs nongenetic factors of the total variation in twin resemblance on the age at onset of regular alcohol use, the age at meeting criteria for a diagnosis of alcohol dependence, and the transition period from regular alcohol use to a diagnosis of alcohol dependence. Results: Genetic influence accounted for 49% of the variation in the age at diagnosis of alcohol dependence. After adjusting for co-occurring psychiatric diseases, additive genetic factors still explained more than 37% of the variance in age at onset of alcohol dependence and at least 25% of the variance in the transition period between regular drinking and the diagnosis of alcohol dependence. Additionally, after grouping participants as early and late regular users of alcohol, the genetic effects on the transition period for early regular users were statistically significantly greater than those for late regular users. Conclusion: Our results demonstrate a substantial heritable basis for alcohol dependence according to its developmental sequence, including age at onset of regular use, age at diagnosis, and the transition period between regular use and diagnosis.
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