Alcohol Dependence
            Heredity and Environment in Alcoholism
    

The Harvard Mental Health Letter, Vol. 9, No.1, July 1992

 
According to a recent twin study, the popular view that susceptibility to 
alcoholism is inherited may be correct only for a small group of men who begin 
to abuse alcohol at an early age in connection with criminal and delinquent 
activity. Three hundred fifty-six clients of various private alcohol and drug 
abuse treatment programs participated in the study, along with their twins -- 
121 pairs of genetically identical and 235 pairs of fraternal twins in all. Of 
these pairs 181 were male, 87 female, and 88 mixed. All the twins answered 
questionnaires on their personal and family histories of psychiatric disorders 
and alcohol and drug use. 
A male alcoholic's identical twin was more likely than his fraternal twin to be 
alcoholic, to have alcohol-related symptoms, to use other drugs, or to have been 
in trouble as an adolescent for antisocial behavior. This difference between 
identical and fraternal twins was significant only if alcohol abuse began before 
the age of 20. In women there was no correlation for alcohol and drug abuse even 
among identical twins. So the heritability of alcoholism was fairly high for men 
who began heavy drinking early, but low for other men and for women. As further 
confirmation of this sex difference in genetic susceptibility, the researchers 
found that when both of two male identical twins were alcoholic, there was also 
a high rate of alcoholism in their families. When both of two female identical 
twins were alcoholic, their families did not have an especially high rate of 
alcoholism. 
But identical twins of female alcoholics did have a high rate of treatment for 
depression and a high rate of illicit drug use (mainly prescription sedatives 
and stimulants). These women may have been using alcohol or other drugs to 
medicate themselves for depression and anxiety, to which they may have been 
genetically vulnerable. 
The lifetime rate of alcohol dependence or alcohol abuse in female twins of male 
alcoholics was nearly five times as high as it was among women in general, and 
the rate among male twins of female alcoholics was three times the average male 
rate. Since the lack of any correlation between female identical twins indicated 
a low hereditary influence on alcoholism in women, the authors conclude that 
something in the environment shared by twins of opposite sex must be associated 
with susceptibility to alcohol abuse. 
Matt McGue, Roy W. Pickens, and Dace S. Svikis. Sex and age effects on the 
inheritance of alcohol problems: a twin study. Journal of Abnormal Psychology, 
101:3-17 (January 1992).



© President and Fellows of Harvard College, 1992. 
Reprinted with permission. 


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