Alcoholism: The Genetic Puzzle (Cont.)

Type 1s and Type 2s

The alcoholics in the Cloninger-Bohman studies fell into two distinct categories. Type 1, the more common form, developed gradually, later in life, and did not necessarily require structured intervention. Type 1 alcoholic men did not always experience the dramatic declines in health and personal circumstances so characteristic of acute alcoholism. These people sometimes straddled the line between alcoholism and “problem drinking.” For Type 1 alcoholics, the genetic inheritance was more like a latent tendency; a propensity that did not automatically show up in every case. It was as if some environmental triggering mechanism, some outside set of circumstances, was required for the inheritance to express itself.

Type 2 alcoholism was a different story altogether. It was bad business from the start; a very unlucky roll of the dice indeed. Type 2 alcoholics were in serious trouble starting with their first taste of liquor during adolescence. Their condition worsened with horrifying speed. They frequently had a history of violent and antisocial behavior, and they often ended up in prison. They were rarely able to hold down normal jobs or sustain workable marriages for long. Type 2s, also known as “familial” or “violent” alcoholics, were even more likely to have had an alcoholic parent. They were, in short, severely addicted to alcohol.

Almost 20 per cent of children born to Type 2 alcoholics became alcoholics themselves. At first glance, this rate does not seem particularly high. The numbers are not as neat and clean as classic Mendelian genetics would have it. But recessive traits are like that. In the case of a recessive gene, inheritance rates are much lower. “Most behaviors,” writes Tabitha Powledge in Bioscience, “do not wend their way through generations in the manner of Mendel’s smooth and wrinkled peas.”  Viewed in that light, 20 per cent is a very high number, and the Stockholm Adoption Study constituted strong evidence for the inheritability of the condition known as alcoholism.

Goodwin’s Danish studies and the Cloninger-Bohman studies were not the only evidence for a genetic connection in at least some cases of alcoholism. In the United States, Remi Cadoret and a team at the University of Iowa studied Iowa adoptees, and came up with similar results. In fact, more than a dozen major studies of twins pointed to the same conclusion:  In alcoholic families, there is a marked difference in alcoholism rates when identical twins (who share the same genes) are compared with fraternal twins (whose genetic makeup differs). If one identical twin is alcoholic, the likelihood that the other identical twin is also alcoholic turns out to be nearly twice as high as it is with fraternal twins. Alcoholism begets alcoholism, even when the alcoholic parent is nowhere on the scene.

Adapted from The Chemical Carousel: What Science Tells Us About Beating Addiction by Dirk Hanson © 2008.

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