Family environmental factors are important contributors to risk for alcohol abuse disorders in youngsters with increased genetic risk for alcoholism, according to an article in the December issue of The Archives of General Psychiatry.

According to the article, although considerable evidence suggests that genetics plays a role in the development of alcohol dependence, the offspring-of-twins design has been used infrequently to assess these effects. This design allows researchers to look at both genetic and environmental risk factors based on a twin's history of alcoholism.

For example, children raised by an alcoholic monozygotic or dizygotic twin parent are at high risk for psychiatric disorders including alcoholism because they have both high genetic and environmental risk factors. Previous studies have shown that children raised by alcoholics are more likely to become alcoholics themselves.

In contrast, children raised by the non-alcoholic monozygotic twin of an alcoholic are at a low environmental risk because the children did not grow up in an alcoholic household. However, these children have the same high genetic risk because the parent siblings have the same genotype. Children raised by the non-alcoholic dizygotic twin of an alcoholic are also at a lower environmental risk for alcohol dependence, but they are at an intermediate genetic risk because dizygotic twins share half of their genes.

Theodore Jacob, PhD, and his American colleagues used the offspring-of-twins design to study the effects of genetics and environment on the risk of developing alcohol dependence. They conducted telephone interviews with 1,213 male monozygotic and dizygotic twins who had been enrolled in the Vietnam Era Twin Registry, which is composed of male-male twins born between January 1, 1939 and December 31, 1957 who served in the U.S. military.

The current study included registry members who had completed an interview in 1992 and reported having children born between 1974 and 1988. The researchers also interviewed 1,270 children of the twins and 862 mothers of these children. The interviews consisted of detailed information about psychiatric disorders including alcohol abuse and alcohol dependence. The average ages of the fathers and mothers were 50 years and 47 years old.

The study design focused on the diagnosis of alcohol abuse or alcohol dependence among children of the twins. Children ranged in age from 12 to 26 years old. Among the children, 276 had twin fathers who had no diagnoses of alcohol abuse or alcohol dependence. In the rest of the children, either their twin father, their twin father's brother, or both had a diagnosis of alcohol abuse or alcohol dependence.

The researchers found that children of monozygotic and dizygotic twins with a history of alcohol dependence were significantly more likely to have alcohol abuse or alcohol dependence themselves than were children of non-alcoholic fathers. Children of an alcohol-abusing monozygotic twin whose co-twin was alcohol dependent were more likely to be alcohol dependent than children of non-alcoholic twins. Children of a monozygotic twin with no history of alcohol abuse or dependence whose co-twin was alcohol dependent were no more likely to be alcohol abusers or alcohol dependent than the children of non-alcoholic twins.

The researchers concluded, "These findings support the hypothesis that family environment effects do make a difference in accounting for offspring outcomes, in particular, that a low-risk environment (that is, the absence of parental alcoholism) can moderate the impact of high genetic risk regarding offspring for the development of alcohol-use disorders."