The brains of alcohol-dependent individuals are affected not only by their own heavy drinking, but also by genetic or environmental factors associated with their parents- drinking, according to a new study by researchers at the National Institute on Alcohol Abuse and Alcoholism (NIAAA).
Researchers found reduced brain growth among alcohol-dependent individuals with a family history of alcoholism or heavy drinking compared to those with no such family history. Their report has been published online in Biological Psychiatry at http://www.sciencedirect.com/science/journal/00063223 as an article in press.
"This is interesting new information about how biological and environmental factors might interact to affect children of alcoholics," notes George Kunos M.D., Ph.D., Scientific Director, Division of Intramural Clinical and Biological Research, NIAAA.
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.
"Our study is the first to demonstrate that brain size among alcohol-dependent individuals with a family history of alcoholism is reduced even before the onset of alcohol dependence," explains first author Jodi Gilman, B.S., a NIAAA research fellow and Ph.D. candidate at Brown University working with senior author Daniel Hommer, M.D., of the NIAAA Laboratory of Clinical and Translational Studies (LCTS) and co-author James Bjork, Ph.D., also of the NIAAA/LCTS.
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 percent 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 note that a possible implication of their findings is that the increased risk for alcoholism among children of alcoholics may be due to a genetic or environmental effect, or both, related to reduced brain growth.
"Although ICV is known to be influenced primarily by genetic factors," says Dr. Hommer, "many studies have found that living in an enriched environment promotes central nervous system growth and development. It seems likely that alcoholics, in general, are raised in less than optimal environments and thus that genetics and environment both contribute to the smaller ICV observed in family history positive alcoholics."
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).
"It is possible that some participants might have experienced subtle fetal alcohol effects," notes Dr. Hommer. "However, there were no differences between the effects of maternal and paternal drinking on ICV of men in our study. Thus, fetal alcohol effects do not appear to account for the reduced ICV we saw in men with a positive family history for drinking. Future studies should determine more precisely how parental drinking affects brain size among children of alcoholics and whether smaller ICV is a more specific risk factor for the development of alcohol dependence than family history."