Fetal alcohol syndrome---where the developing fetus is exposed to high levels of ethanol in the womb---has far-reaching negative effects on neural development. Now environmental and biological factors of parental alcohol abuse might also retard brain growth, according to a new study published in Biological Psychiatry.

Many studies have shown that alcohol-dependent men and women have smaller brain volumes than non-alcohol-dependent individuals. It is widely believed that this is due to the toxic effects of ethanol, which causes the alcoholic's brain to shrink with aging to a greater extent than the non-alcoholic's.

Children of alcoholics are known to have a greater risk for alcohol dependence than individuals without a parental history of alcohol dependence. In addition to inheriting genes that predispose them to alcoholism, children of alcoholics may experience adverse biological and psychological effects from poor diets, unstable parental relationships, and alcohol exposure before birth, all of which could contribute to their increased risk for alcoholism.

In a search for direct physical evidence of these assumed genetic and environmental mediators of family-transmitted alcoholism, the NIAAA researchers used magnetic resonance imaging (MRI) techniques to measure the volume of the cranium -- the part of the skull that encloses the brain -- in a group of individuals being treated for alcohol dependence. The intracranial volume (ICV), they note, is determined by skull growth, which occurs as the brain expands to its maximum size around puberty. Because ICV does not change as the brain shrinks with age, it provides a good estimate of the lifetime maximum volume of the brain.

The researchers found that the average ICV of adult alcoholic children of alcoholic parents was about 4% smaller than the average ICV of adult alcoholics without family histories of alcoholism or heavy drinking. Family history did not affect the frequency, quantity, or other aspects of drinking behavior of the alcoholics themselves, suggesting that differences in ICV between family history positive and negative alcoholics are not the result of different drinking patterns. The researchers also found that adult alcoholic children of alcoholic parents had IQ scores that averaged 5.7 points lower than IQs of alcohol dependent individuals with no parental drinking, but that were still within the range of normal intelligence.

The authors report that ICV of women, but not men, in the study appeared to be affected more by their mothers' drinking than their fathers', perhaps due to a greater maternal influence on a child's nutritional, social, and intellectual environment. None of the participants in the study were diagnosed with fetal alcohol syndrome (FAS).