Twin Studies of Alcoholism

That risk-related behaviors are evident early in life, remain stable into adolescence, and are associated with a family history of alcoholism suggests that those behaviors are, at least in part, of genetic origin. To establish that, researchers must use genetically informative study designs.

One approach is to study child or adolescent twins and their parents. Several such studies, which specifically assess the initiation of alcohol use and the transition to alcohol abuse, are being conducted throughout the world. We illustrate with two ongoing studies from Finland.

One, "FinnTwin12," is a study of approximately 2,800 twin pairs and their parents. The twins represent all pairs from five consecutive twin-birth cohorts (1983-1987) who were entered into the study as they reached age twelve (1995-1999), when behavioral ratings by teachers and parents were obtained on all participating pairs.

The ratings include multidimensional scales (i.e., scales that rate various characteristics) of behaviors associated with increased alcoholism risk. Two years later, at age fourteen, the twins were followed up, and, while most reported abstinence, about one-third were then using alcohol.

What predicts drinking or abstaining at age fourteen? Genetic factors played a role only among twin sisters, perhaps reflecting their more accelerated pubertal maturation, and environmental effects shared by twin siblings accounted for most of the variation in drinking or abstaining at this age. Differences that twins attributed to their home environments (e.g., in parental monitoring, support, and understanding) and differences in teachers' ratings of twins' behavior at age twelve (in problem behaviors of aggressiveness, impulsivity, and inattention) differentiated those who were drinking from those still abstaining at fourteen.

But once drinking is initiated, genetic effects become evident in individual differences in frequency and quantity of consumption and in behavioral problems that then result. "FinnTwin16," another study of five consecutive, complete birth cohorts of Finnish twins, illustrates. These twins were first studied as they reached age 16, with follow-up twelve and thirty months later, at ages 17 and 18V2. At age 16, about 25 percent had remained abstinent.

Of 2,810 twin pairs, both twins in 459 pairs (16.3%) were abstaining, co-twins in 1,964 pairs (69.9%) had concordantly begun drinking by age sixteen, and only 387 pairs were discordant, with one twin drinking and the

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