Evidence for specificity of transmission of alcohol and nicotine dependence in an offspring of twins design.

Alcohol dependence (AD) and nicotine dependence (ND) have been shown to co-occur. Results from twin studies implicate the role of genetics in the etiology of both ND and AD with substantial, yet incomplete, overlap. To test for specificity of transmission of AD and ND in an offspring of twins sample we analyzed data from a study of adolescent and adult offspring of twin fathers ascertained from the Vietnam Era Twin Registry. This sample consists of 1213 twin fathers, 862 biologic or rearing mothers, and 1270 offspring. Offspring were allocated to one of four risk groups for AD based on twin fathers' zygosity and father's and cotwins AD history. Offspring DSM-IV AD and ND were measured by structured diagnostic interview. Paternal AD and ND were significantly associated with offspring AD and ND, respectively. Bivariate probit regression results suggest specificity for transmission of AD and ND. This remained constant after controlling for offspring demographics and psychopathology and maternal AD and ND. Despite the substantial genetic overlap between the two disorders, there is evidence for genetic effects specific for AD and ND.