Medicine: Out in the Open

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But it was still far from clear how hereditary and environmental factors combine to create an alcoholic. In the early 1980s, Cloninger joined a team of Swedish investigators led by Michael Bohman, a psychiatrist at the University of Umea, to study an even larger group of adoptees. Since Sweden's extensive welfare system keeps thorough records on each citizen, Bohman was able to compile detailed sketches of 1,775 adopted men and women, more than a third of whom had an alcoholic biological parent. As Cloninger studied the health, insurance, work and police records of his subjects, two distinct categories seemed to emerge -- and with them new evidence that alcoholism may have more than one form.

Cloninger's first group of alcoholics, about 25% of the total, tended to drink heavily before the age of 25, had bad work and police records and met with little success in treatment programs. Drinking was a habit they seemed to pick up on their own, with little encouragement from friends or other influences. When Cloninger checked how often alcoholism appeared in the sons of men who fit this description, he found it surfaced nine times as often as in the general population. This variation of the disease, Cloninger concludes, is heavily influenced by heredity. Because it appears primarily in men, he calls this form "male limited" alcoholism.

The second type included both men and women and made up about 75% of the study's alcoholics. They started chronic drinking usually well after the age of 25, rarely had trouble with the law, and often successfully kicked the habit. Their children were only twice as likely to have trouble with alcohol compared with the general population. Cloninger labeled this category of alcoholism "milieu limited," indicating a genetic predisposition to the disease that is triggered by extended heavy drinking.

Cloninger's work added key pieces to the puzzle of alcoholism by suggesting traits that certain types of alcoholics have in common. For example, Cloninger found that his male-limited alcoholics tended to be aggressive, even violent types. He hypothesizes that the nervous system underlying such behavior may react to alcohol in a way that quickly leads to dependence. "It's not proved," says Cloninger. "It's testable." Says Boris Tabakoff of the NIAAA: "For those of us looking for biological markers, Dr. Cloninger's work gives us a road map we can follow to link genetic traits to behavior."