Alcohol and Genetics: Nature vs. Nurture
written by: Melissa Jessup
When it comes to behavioral patterns, there has been a long-
going controversy as to whether a variety of complex behaviors
exhibited in animals are more dependent upon nature or nurture.
Addiction is one such behavior that falls under the controversy.
Although alcohol addiction has traditionally been viewed as a vector of
environment, studies in more recent years have indicated that
alcoholism also has a strong genetic component. The question remains
which factor, if either, has a stronger contribution to alcohol
dependence.
There are four main points that need to be considered for
environmental influences. The first point is that alcoholics generally
make bad parents. An alcoholic is not going to be a stable role model
in a child's life, and is likely to inflict severe emotional damage,
causing the child to then turn to alcohol themselves. Another point is
that an individual who is frustrated in life, insecure, and generally
unhappy may continuously turn to alcohol to escape the reality of life.
A third point is that children learn from their parents. If a child is
exposed to alcoholism at an early age, he or she will learn that it is
acceptable. Likewise, if a child sees that his or her parents use
alcohol as a means to deal with life's obstacles, then that child will
learn the same behavior. Finally, the most obvious environmental
factor is that alcoholism cannot occur with out alcohol. If a person
does not have access to alcohol, he or she will not become dependent on
the substance, (Goodwin, 1988).
While genetic factors alone cannot account for a person's risk,
they have been shown to be a strong predictor for alcoholism.
Biological family studies have revealed that children of alcoholics
often exhibit a wide range of characteristics associated with their
parents' addiction. It was found that children of alcoholics are more
likely to be alcoholic themselves (Cotton, 1979). and to have other
behavioral and psychiatric problems such as anxiety and depression,
(West and Prinz, 1987; Sher and Trull, 1994). A review of several
studies by Goodwin (1979), showed that about twenty- five percent of
fathers, as well as brothers, of an alcoholic are also alcohol abusers.
Another study reported that eighty percent of a sample of treated
alcoholics had at least one biological first or second degree relative
who was also alcoholic, (Hesselbrock, et al., 1992). Compared with
children of non- alcoholics, children of alcoholics have a higher
tolerance for alcohol, and they are more often hyperactive. Children
of alcoholics also generate more alpha activity on
electroencephalograms (EEGs), and under respond to certain stimuli
recorded on EEGs (Goodwin, 1988).
Due to the fact that adopted children presumably share genetic
factors with only their biological parents and environmental factors
only with their adoptive parents, adoption studies have given a direct
approach to looking at the respective contributions of genetic and
environmental factors in alcoholism. Among several adoption studies,
the most significant finding is the strong correlation between
alcoholism between male adoptees and their biological parents. The
rate of alcoholism in adoptees has been found to be two to three times
higher in sons of alcoholics than the adopted- away sons of
nonalcoholics, (McGue, 1995). The Stockholm Adoption Study
(Sigvardsson et al., 1996), studied 862 men who had been adopted in
infancy, along with their biological and adoptive parents. Results
showed that among the adoptees, the rate of alcohol abuse was 14.7
percent if neither biological parent was alcoholic, 22.4 percent if
only the biological father abused alcohol, 26.0 percent if only the
biological mother abused alcohol, and 33.3 percent if both biological
parents were alcoholics. Among female adoptees with alcoholic mothers
the rate of alcoholism was 9.8 percent, while the rate of alcohol abuse
among female adoptees of nonalcoholic mothers was 2.8 percent.
Studies on monozygotic and dizygotic twins also have relevance in
finding the genetic evidence for alcoholism. In one study of 86 pairs
of male twins, the concordance rate for alcohol dependence was fifty-
nine percent among monozygotic twins, and only thirty- six percent
among dizygotic twins, (Pickens et. al., 1991). Earlier twin studies
of diagnosed alcohol dependence have showed similar, although weaker
correlations. In 1981, Gurling el. al. showed a thirty- three percent
alcoholic concordance between fifteen monozygotic male twins, and a
twenty- five percent concordance between twenty- eight dizygotic male
twins. Female twins showed an eight- percent concordance among
thirteen monozygotic twins and thirteen percent for eight dizygotic
twins.
Genetics have even been shown to play a role in metabolizing
alcohol, (Li, 1999). Alcohol dehydrogenase (ADH) and aldehyde
degydrogenase (ALDH2), the mitochondrial form of ADH, are the two liver
enzymes that are most responsible for the metabolism of alcohol. When
alcohol is consumed, ADH serves to oxidize ethanol into acetaldehyde.
ALDH2 then oxidizes acetaldehyde into acetate, with is metabolized into
carbon dioxide and water in other tissues throughout the body. The
ADH2 gene is responsible for encoding the beta subunit of alcohol
deydrogenase, while polymorphic forms of the enzyme are encoded by
different gene alleles, namely ALDH2*1, ALDH2*2, and ALDH2*3. There
are variants of these enzymes, all of which differ in catalytic
properties. While some of the enzymes have a low activity and high
affinity for ethanol alcohol, others have a high activity and lower
affinity for ethanol, and are therefore not restricted in activity by
higher alcohol concentrations. The enzyme encoded by the ALDH allele
called ALDH*2 degrades acetaldehyde more slowly than normal, resulting
in the prolongation of certain unpleasant alcohol effects, such as
facial flushing, palpitations, and nausea, This particular enzyme
varies in ethnic populations throughout the world, and it has been
found that people who carry the allele are less likely to consume
alcohol and to develop alcoholism than people without the allele,
(Crabb, Edenberg, Thomasson, and Li, 1995).
Very recently, a study by Nernberger, et. al., (2001) found
evidence that a locus on chromosome 1 is responsible in influencing the
vulnerability to alcoholism. The same locus also appears to influence
the risk for phenotypic depression in individuals. The correlation
between affective disorder and alcoholism has long been noted.
Although it could be a side effect of alcoholism, major depression has
been found to be more prevalent in alcoholic than in nonalcoholic
individuals in families with multiple alcoholics, (Nernberger, et. al.,
2001). As noted in data from the National Institute of Mental Health,
bipolar male subjects have almost a twofold risk of alcoholism, while
the alcohol abuse risk of bipolar women was nearly sevenfold,
(Nernberger, et al., 1996). For the past ten years, investigators
across the United States within the Collaborative Study of the Genetics
of Alcoholism have gathered clinical information and biological data
from families with multiple (3 or more) alcoholic individuals. A
nonparametric linkage analysis on sibling pairs was performed in order
to identify chromosomal regions linked to the three phenotypes of
alcoholism, depression, and comorbid alcoholism and depression. An
analysis for all possible pairs of affected siblings showed that the
highest logorithm of the odds ratio for linkage (lod) score was found
on chromosome 1.
In the case of nature versus nurture, it seems that both factors
could be equally important. As evidence has shown, genes play a large
role in a person's potential behavior and habits. Environmental
factors and situations, however, are what allow seemingly predisposed
behaviors to emerge. Alcohol addiction is a good candidate for the
continuing study of genetic and environmental factors, and how they
affect individuals. The more we continue to understand about
alcoholism, the more can be done to help control it.
References
Crabb, D., Edenberg, H., Thomasson, H, and Li, T. (1995). Genetic
factors that reduce risk for developing alcoholism in animals and
humans. The Genetics of Alcoholism, Oxford University Press, New York,
202-220.
Li, T. (1999). Pharmacogenetics of responses to alcohol and genes that
influence alcohol drinking. Journal of Studies on Alcohol, 5-11.
Goodwin, D. (1988). Is Alcoholism Hereditary? Ballantine Books, New
York.
Martin, N. (1987). Genetic differences in drinking habits, alcohol
metabolism and sensitivity in unselected samples of twins. Progress in
Clinical and Biological Research, 241, Alan R. Liss, Inc., New York,
109-119.
McGue, M. (1997). A behavioral- genetic perspective on children of
alcoholics. Alcohol, Health, and Research World, 21 (3), 210-217.
Nurnberger, J., Foroud, T., Flury, L., Su, J., Meyer, E., Hu, K.,
Crowe, R., Edenberg, H., Goate, A., Bierut, L., Reich, T., Schuckit,
M., and Reich, W. (2001). Evidence for a locus on chromosome 1 that
influences vulneralbility to alcoholism and affective disorder.
American Journal of Psychiatry, 158, 718-724.
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Copyright © 2001, Dr. John M. Morgan, All rights reserved -
This page last edited 8 May, 2001
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