Inheritance of Alcoholism

Inheritance of vulnerability to substance use disorders has been an issue provoking controversy in the past, at times sparking sharp "nature vs. nurture" debates. Clarifying the matter is of much more than just academic interest because of the effect on prevention and treatment strategies as well as on attitudes. As new studies are completed, they tend to support the existence of a genetic factor. The evidence is stronger for alcohol, which is easier to study than other drugs

The most consistent and least controversial finding is that alcoholism tends to run in families. Furthermore, as the closeness and number of alcoholic relatives increase, so does the risk that the individual will become alcoholic. If a parent is alcoholic, his or her child is four times more likely to become alcoholic than is the child of a non-alcoholic parent.

More specific to the genetic issue are twin and adoption studies. Identical twins are more likely to both be alcoholic than are fraternal twins. Children of alcoholic parents who are adopted away at birth show the same fourfold increased risk of alcoholism. Adoption of a child of a non-alcoholic into an alcoholic home does not create increased risk. Thus the increased risk is clearly determined by the biological parent.

Many questions regarding the inheritance of substance use disorders are best addressed through "prospective" rather than "retrospective" studies. Such a study has been conducted by Dr. Marc Schuckit, who has been following a group of 453 men since 1975. First seen at age 20, those with a positive family history (PFH) of alcoholism were matched with controls who were without such a history (NFH).

In the initial evaluation, no differences were found between the two groups in personality tests or in their blood alcohol levels following the ingestion of alcohol. A significant difference, however, was found in their response to alcohol as determined by subjective reports of intoxicated feelings, objective measurements of unsteadiness, and determination of blood hormone levels. An abnormally low response was found in 40% of those with PFH, but in only 5% of those with NFH.

Re-evaluation of the men after 15 years has revealed that a high incidence of alcoholism is developing among those with low responsivity to alcohol, whether they had PFH or NFH. There has been, however, no increased risk of depression, anxiety, or problems with other drugs. These findings would suggest that persons with unusually high tolerance for alcohol, especially if they have a positive family history, should be alerted to their greater risk of developing alcohol problems.

A genetic or biological vulnerability to alcohol problems is a statistical possibility, not a certainty. A pertinent question is why some individuals develop the actual clinical syndrome, while others do not. One answer lies in the interaction with psychological and social factors. While no pre-existing "addictive personality" has been documented, three psychological and social features were found to amplify the biological vulnerability. Those men in the study who had low responsivity to alcohol and who also were impulsive or easily bored had an increased likelihood of becoming alcoholic. High levels of work stress had the same effect.

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