It involved 2,685 pairs of twins, all participants in an adult twin study started in Australia in 1978 and maintained by the Australian National Health and Medical Research Council. The two members of each pair were raised in the same home environment. Through telephone interviews with the twins, researchers assessed whether the participants had lost control over their drinking, were unable to cut back on drinking or had similar problems with alcohol. More surprisingly, men who had an alcoholic twin sister had very high rates of alcoholism. That wasn't the case.
Monozygotic twins share the same genetic makeup.
Dizygotic, or nonidentical, twins are not more alike genetically than ordinary siblings. In the study, a dizygotic twin was only three times more likely to be alcohol dependent if her twin had a drinking problem. The study also examined whether psychiatric disorders that commonly precede or coexist with alcoholism, for example, childhood behavior problems such as lying and stealing or depression, were as strongly associated with risk of alcoholism in women as in men. We found that depression is a potent predictor for alcohol dependence in both men and women. The researchers acknowledge there still is much to learn about how and why alcoholism manifests itself.