by: Kenneth Blum, Ph.D.

By the beginning of 1989, scientists were generally agreed that genetic anomalies were the primary causative factor in at least some forms of alcoholism. There were those who disagreed, but genetic predisposition toward craving for alcohol was firmly established in both the scientific and treatment communities. Where the predisposition was present, environment could act as a triggering factor. In some cases where there was no predisposition, environment - long-continued stress or persistent heavy drinking - might bring about bodily changes leading to craving. But the genetic factor was coming to be regarded as a major key to alcoholism, thereby strengthening the disease concept.

Animal Genetics

Early support for the genetic factor began to appear as early as 1949, when Korge Mardones found that some rats, when deprived of vitamin B complex, developed a craving for alcohol. When Mardones bred these animals, he found that, seven generations later, their off- spring also preferred alcohol over water. This suggested that both nutrition and genetics might affect alcohol craving.

In 1969, Gerald McClearn set out to develop an animal model of alcoholism. Through selective breeding - without environmental manipulation - he developed several strains with varying degrees of alcohol preference. For ex- ample, the C 57 black mice loved alcohol; the DBA mice hated it. Because they bred true, they became a powerful research tool. By experimenting with alcohol-preferring and alcohol-nonpreferring mice, they could study differences in brain chemistry, metabolism, and alcohol effects.

The success of these animal models led to a tremendous expansion in animal work on alcoholism. In America, Finland, and Italy, for example, rat models were developed. One of the most important was the rat model of T. -K. Li: P (preferring) and Non-P (nonpreferring) rats. His P rats drank as much as 65 percent alcohol by preference and experienced withdrawal symptoms similar to those of humans.

Using alcohol-preferring and non- preferring animals, scientists were able to demonstrate differences in neurochemistry - particularly in the reward areas of the brain - and in the neurochemical effects of alcohol. These Findings led to new insights into the biogenetic causes and progression of alcohol-craving behavior in humans.

Human Genetics

The first strong indications of a genetic factor in humans came in 1972, when M.A. Schuckit and D.W. Goodwin mounted a study in which they found that children of alcoholic parents had the same rate of alcoholism regardless of whether they were brought up in their parents' home or adopted into a nonalcoholic home.

Shortly afterward, Goodwin and George Winokur studied 5,483 adoptees in Denmark and found that sons of alcoholics adopted by other families were more than three times as likely to become alcoholics as the adopted sons of nonalcoholics.

Michael Bowman, in Sweden, studied 2,324 adoptees and their biological parents, and found that adopted sons of alcoholic fathers were three times more likely to become alcoholics than adopted sons of nonalcoholic fathers. Adopted sons of alcoholic mothers were twice as likely to become alcoholics as those whose mothers were nonalcoholics.

Many attempts have been made to describe alcoholic types, beginning with J.M. Jellinek, but the disease is so complex that such categorization is difficult. The most recent is by Robert Cloninger: milieu-limited, which requires both a genetic predisposition and environmental influences as a trigger, and male-limited, which occurs only in men and is primarily genetic in origin. Like the other attempts, this effort at classification has met with mixed reactions among scientists and therapists. My colleagues and I believe that these efforts to characterize the phenotype need to be strengthened by information characterizing the genotype before definitive typing can take place.

Further clarification of the role of genetics came from the effort to find electrophysiological markers indicating a predisposition to alcoholism. Henri Begleiter measured P300 wave activity evoked by specific stimuli in young sons of alcoholic fathers and compared this to P300 wave responses in sons of nonaicoholic fathers. He found a markedly reduced amplitude in the waves of sons of alcoholic fathers, which he considered were genetic antecedents of alcohol abuse. He raised the question, however as to whether this deficit had beer transferred from father to son, and thi further question as to whether this defi cit in the son would lead to future drug or alcohol abuse.

Ernest Noble addressed both questions in experiments carried out in the las four years and found affirmative an swers to both questions. The alcoholif fathers had the same P300 wave deficit as their sons, and the sons showed increased alcohol-, cigarette-, and marijuana-seeking behavior compared to sons of nonalcoholic fathers. Noble also found that these same sons of alcoholic fathers had an atypical neurocognitive profile.

The Cascade Theory of Reward: A Blueprint for Mapping Alcogenes

In my laboratory we have been investigating the role ofneurotransmitters in craving behavior and now integrated our findings and those of others into a coherent pattern: the Cascade Theory of Reward. In normal individuals, neurotransmitters - the messengers of the brain - work together in patterns of stimulation or inhibition, the effects spreading downward from complex stimuli to complex patterns of response like a cascade, leading to feelings of well-being and reward.

If a genetic deficiency blocks or distorts this cascade, the result is a tendency toward anxiety, anger, low self-esteem Or other "bad feeling," or toward craving for a substance that will make the bad feeling go away - alcohol, for example. An earlier version of this theory was published in this magazine in 1988; the current version is presented in Figure 1. This schematic became the blueprint for our search for the alcogene.

Animal-model support for the cascade theory can be derived from a series of experiments carried out by T. -K. Li and associates on their alcohol-preferring (P) and nonpreferring (NP) rat lines. They found that the P rats had:

• lower serotonin neurons in the hypothalamus;
• higher levels of enkephalin in the hypothalamus;
• increased serotonin receptors;
• more GABA neurons in the nucleus accumbens;
• reduced dopamine supply at the nucleus accumbens.

This suggests a four-part cascade sequence leading to a net reduction of dopamine release in a key reward area. This was further confirmed when they found that, by administering substances that increase the serotonin supply at the synapse or by stimulating dopamine D2 receptors directly, they could reduce craving for alcohol. Both dopaminergic agonists as well as serotonin receptor inhibitors significantly facilitate abstinence in alcoholics. Human support for the cascade theory also can be derived from a series of experiments involving clinical trials with neuronutrients (pre- cursor amino acid loading techniques and enkephalinase inhibition) indicating reduced drug hunger, reduced stress, reduced AMA rates, and facilitated recovery with less relapse.

The problem faced by Dr. Ernest P. Noble, Pike Professor of Alcohol Studies at the University of California at Los Angeles, and I, as we approached the design of our experiment, was the sheer complexity of the genetic patterns of the brain. There are billions of neurons and a hundred thousand genes in 46 packages called chromosomes. These chromosomal packages act in pairs, so there are 23 pairs in each cell. Half of the chromosomes come from the mother and half from the father. Together, the genes contain the information necessary to control the generation of all proteins and enzymes necessary for life and function. Obviously, if there is a defect in a gene, the structure or function of the body will be affected. The question we faced was how could we find the gene or genes responsible for alcoholism? It was like looking for the proverbial needle in a haystack.

The cascade theory simplified the problem by suggesting genes known to control enzymes and receptors involved in reward, and whose irregularities had been associated with alcoholism. Some of the possible candidates were genes that control the enzymes involved in production or breakdown of serotonin, dop amine, and norep inephrine and their receptors; and protein precursors in- volved in the production ofenkephalins and endorphins. This reduced the mag- nitude of the problem from a hundred thousand possibilities to less than 100, but it was still too formidable. Even if we knew the exact gene, how could it be identified in the complexity of the DNA structure - the human genome?

The RFLP Technique

A new technique called "restriction fragment length polymorphism" (RFLP) gave us the tool we needed. This makes it possible to identify variations in the DNA of human chromosomes that can act as genetic landmarks for defective genes responsible for a given disease. Our colleague. Dr. Peter Sheridan, a molecular biologist in the University of Texas Health Science Center at San Antonio, had worked with the technique, and he confirmed our belief that it would be useful in identifying the gene or genes responsible for alcoholism.

To understand how the RFLP technique works, consider the structure of the DNA. As shown in Figure 2, DNA is a twisted ladder, each side rail a DNA strand, and each rung a pair of chemical bases. Each of the four bases - adenine, guanine, cytosine, and thymine - can pair only with one of the other bases; that is, G with C, and T with A.

Two special terms must also be understood:

• "Restriction enzymes" are special enzymes that act only at certain base pairs in a specific sequence of genes in a DNA stand. They act to cut the DNA at those sites only.
• "Probes" are short lengths of DNA, obtained from natural sources or made synthetically, that are complementary to the candidate gene in the genome.

Finding a Suspect Alcogene

In applying the technique, shown in Figure 3, the DNA is cut by the enzyme, and the probe is made radioactive and inserted into a gel containing the DNA fragments. The probe binds to the complementary DNA fragment containing the target gene and, because it is radioactive, identifies the site by "lighting up" a photographic film.

Before we could begin our exp eriment, we needed a road map of DNA that would identify likely sites for the suspect gene or genes; a source ofDNA specimens from a good sample of known alcoholics; and DNA probes that could be sent in like ferrets to locate the abnormal gene or genes.

We had the roadmap in the cascade theory; we had the DNA samples in a five-year collection of 35 alcoholic and 35 nonalcoholic brains assembled at UCLA; and we were fortunate in having access to some 40 candidate gene probes from sources all over the world. The brain samples were particularly usefu because alcoholism is a very complex disease that appears in multiple forms, and good genetic research requires good phenotyping. The alcoholic brains in our sample were all identified with a particularly "virulent" form of alcoholism causing multiple relapses and eventual death. All of the brains, both alcoholic and nonalcoholic, had been rigorously diaggnosed by two independent psychiatrists using DSM III criteria.

It is important to note that this was a "blind" experiment, in that the experimenters in the San Antonio laboratory did not know which of the samples were from alcoholic brains and which were from normal brains. This information was held only by the experimenters in the UCLA labratory.

In the experiments, after cutting the DNA into fragments with particular enzymes, applying the probes, and exposing the sample to a phtographic film, we were looking for three possible out-comes:

• The DNA patterns would all be the same, indicating no variation or "poly-morphism";
• The patterns would be different but not linked to alcoholics or nonalcoholics in the sample;
• The patterns would be different and linked to alcoholics or non-alcoholics.

For example, when we probed for the gene that cdontrols the breakdown of enkephalin, the patterns were all the same - no polymorphism.

When we probed for the gene that regulates the production of alcohol dehydrogenase - the enzyme involved in the breakdown of alcohol - we found a pattern variation, but there was no association with alcoholism.

After a frustrating year of failure, we succeeded in obtaining a probe for the dopamine D2 receptor gene from Olivier Civelli at the Oregon health Sciences University in Portland. Thiswas an exciting moment because the cascade theory indicated a strong correlation between the D2 receptors and reward. When we ran the experiement and inspected the photographic film, we were delighted to find a polymorphism that was strongly associated with alcoholism.

As shown in Figure 4, the DNA sample on the left, showing two bands, represents one individual from the sample; the one on the right, showing three bands, represents another. In the total sample:

• Twenty-seven of 70 brains showed the 10.5 kb band, the 6.6 kb band, and the 3.7kb band;
• Four showed the 10.5 kb band and the 6.6 kb band;
• Thirty-nine showed the 10.5 kb band and the 3.7 kb band.

The important difference was the presence or absence of the 6.6 kb band, termed the Al allele, and the 3.7 kb band, termed the A2 allele. The 10.5 kb band was constant. The Al allele and the A2 allele were polymorphisms, representing anomalies in the gene. When the UCLA experimenters matched the data to the actual brains, they found that 69 percent of the alcoholics in the sample had the Al allele, and 80 percent of the nonalcoholics did not.

When they lined up all of the A1 alleles and all of the A2 alleles, as shown in Figures 5 and 6, the San Antonio team found they had correctly classified 72 percent of the alcoholics and 77 percent of the nonalcoholics. In other words, there was a high probability that we had found an unusual pattern or defect in the dopamine D2 receptor gene, or an- other gene close to it on the chromosome. associated with a virulent form of alco- holism.

However, these findings also sup- ported the idea that there may be several types of alcoholism. Thirty-one percent of the alcoholics in the sample did not associate with the allele, suggesting there may be more than one gene involved and that in some cases environment may be the causative as well as the triggering factor. Furthermore, 20 percent of the nonalcoholics had the Al allele, sug- gesting the possibility that this gene may cause anomalies other than alcoholism.

The Dopamine D2 Receptor Gene and Reward

As shown in Figure 7, chromosome 11, the site of the dopamine D2 receptor gene, has been implicated not only in alcoholism but also in other aberrant behaviors. For example, the gene that controls the enzyme tyrosine hydroxylases, which is involved in the synthesis of dopamine and norepinephrine, has been implicated in manic-depressive illness. In numerous studies, the dopamine D2 receptor has been implicated

in various compulsive pleasure-seeking behaviors including drug abuse, exces- sive sex, and eating disorders. This sug- gests the possibility that, as well as find- ing an alcogene, we have found a gene associated with aberrant pleasure- and reward-seeking behavior. A Word of Caution

In the paper published in the Journal of the American Medical Association on April 18,1990, we pointed out that this initial finding was based on a limited sample; that other genes and such other factors as environment must be consid- ered; and that future work must include DNA obtained from large groups of living alcoholics and their relatives.

We now realize that there is another problem that will be faced by other researchers seeking to replicate or extend our findings: The alcoholics in our sample were all representatives of a particularly virulent form of the disease, characterized by repeated relapses and eventual death due to alcohol-related problems. In addition, they were all 50 years of age or older, which meant they had years of opportunity to break the habit. These two factors make phenotype determination more difficult, particularly when living alcoholics are involved. It may prove that, insofar as alcoholism is concerned, the Al allele is specific for this virulent form.

Another interesting question was: Is it possible that these genetic anomalies were consequences of alcohol abuse, rather than causes of alcoholism?

Fortunately, that question had already been answered by Olivier Civelli and his group. They found the presence of the Al allele of the dopamine D2 receptor gene in 39 children who had not been exposed to alcohol. This indicates that this polymorphism is genetically trans- mitted, not the result of alcohol intake. Implications for Now and the Future

If our findings are correct, they constitute a powerful argument in favor of the disease concept of alcoholism and the importance of the genetic factor. This controversy is still raging, and in many quarters alcoholism is still considered a product of weak moral character and lack of will power. Even the U.S. Supreme Court seemedto side with this viewpoint in a much-publicized 1988 decision. We hope that our findings will remove much of the stigma, enable more individuals to accept their craving as a symptom of an illness, and make it easier for them to seek treatment and affiliation with self-help Twelve Step programs.

For the future, the first step we can envision is the development of a diagnostic tool - a blood test, for example - that will identify children at risk in alcoholic families. We used brain tissues for our experiments, but using DNA derived from lymphocytes will enable us to test living subjects and large pedigrees.

As more is learned about genetic anomalies and their effect on the brain's neurochemistry, we may be able to design more effective adjuncts to treatment; in other words, fine-tune our pharma- cological intervention in terms of genotype as well as phenotype.

Several questions growing out of the experiments also need to be answered. Is the D2 receptor gene itself the direct cause of the alcohol syndrome? Or is it another gene nearby on the chromosome? Or is it two or more genes working together? Does the fact that one-third o the alcoholics in the sample did not show the Al allele indicate that other, as yet undetected, genes may be involved? Or that some forms of alcoholism develop from environmental rather than genetic causes?

Furthermore, the question of privacy and labelling of individuals who test positive for this or other putative alcogenes is cause for concern. With blood tests plausible within the next five years, will children who test positive be branded "alcoholic?" Will they be discriminated against because of this label? What if an employer or insurance company finds out that a person has alcogenes? What about entrance to health professions as well as other critical societal professions for individuals testing positive for these genes? These are disturbing questions with no simple answers, but progress in the genetics of alcoholism and other compulsive dis- eases must be pursued with great vigor if we want to truly understand their root causes.

These questions would have been pointless only a few years ago. We did not have the insights, the knowledge base, the technology, or the techniques to seek the answers. We had not yet made the leap to the concept of somatopsychic disease in which neurochemical imbalances or deficiencies - often resulting from genetic anomalies - lead not only to physical disabilities but to behavioral aberrations as well. But now we have the concepts and, increasingly, the tools to research and understand many diseases that once were cloaked in mystery. It is our hope that out of this research will come knowledge that will enable us to prevent, treat, and cure a wide variety of diseases, including such compulsive diseases as alcoholism and drug addiction.

Acknowledgements
We wish to acknowledge the contribution of James E. Payne, executive director of the National Foundation for Addictive Diseases, to the writing of this paper; the work of Charles Whitehead in graphic design; and that of Al Julian and Phred Peterson in photography.

Suggested Reading

1. Blum, K. A commentary on neuro-
transmitter restoration as a common
mode of treatment for alcohol, co-
caine, and opiate abuse. Integrative
Psychiatry 6:199-104, 1989.

2. Blum, K. and Koriowski, G.P. Etha-
nol and neuromodulator interactions:

A cascade model of reward. In: Prog.
Alcohol Res. 2, Ollat et al. (eds) VSP,
Utrecht, pp 131-149, 1990.

3. Blum, K.; Noble, E.P.; Sheridan, P.J.;<
Montgomery, A.; Ritchie, T.;
Jagadeeswaran, P.; Nogami, H.; Briggs,
A.H.; and Cohn, J.B. Allelic association
of human dopamine D2 receptor
gene in alcoholism. JAMA 263:2055-2060,1990.

4. Brown, R.J.; Blum, K.; and
Trachtenberg, M.C. Neurody-namics
of relapse prevention: aneuronutrient
approach to outpatient DUI offend-
ers, Journal of Psychoactive Drugs
22:173-187, 1990.

5. Cloninger, C. R., and Li, T. -K. Alco-
holism: an inherited disease, DHHS
Publication No. ADM 88-14 26,1988.

6. Noble, E.P. Alcoholic fathers and
their sons. In: Banbury Report 33:

Molecular Genetics and Biology of
Alcoholism. Cold Spring Harbor, NY.
Laboratory Press (In Press) 1990.

7. Seventh Special Report to the U.S.
Congress on Alcohol and Health.
DHHS Publication No. ADM 90-1656,
1990.

8. Whipple, S.C.; Parker, E.S.; Noble,
E.P. An atypical neurocognitive pro-
file in alcoholic fathers and their sons,
Journal of Studies on Alcohol 49:240-
244,1986.

Return to Articles Catalog

Articles Library
Article Catalog
Product Overview
Academic Doping of America
Addictions
The Pursuit of Normalcy