Teasing Out the Genetic Links in Alcoholism

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The search for the genes underlying alcohol addiction continues, and a report to be published in Alcoholism: Clinical & Experimental Research gives more evidence for a cannabinoid receptor making a key difference. The study was released in preview (abstract here) for inclusion in the February, 2012 issue.

Cannabinoid receptors in the brain have been suspected as critical in many addictions. What this study shows is a link between certain forms of the receptor (from differences in DNA) and whether people will become alcohol dependent. The distinction is important. Those who abuse alcohol may not be addicted to it, even though they are frequent users. This work separated out two categories of subjects – those who are actually dependent on alcohol and those who simply abuse alcohol (both types are referred to commonly as alcoholics). In a sense, there are two different problems and we’d like to know the genetic basis for the difference.

At issue is the Cannabinoid receptor 1(CNR1). The name comes from historical research that found the active ingredient in marijuana bound to this location. Since then, it has been determined that the site isn’t specific to cannabinoid, but the name remains. Instead, it seems this receptor site is involved with other substances of abuse as well. The “site” is actually a protein, and this can come in many forms, depending on the gene sequence a particular individual is born with.

To get an idea of the complexity involved, the CNR1 gene comes in at least 10 different variants, and any particular person may have a mix of these (one type from their mother and one from their father). This study looked at three different haplotypes. A haplotype is a combination of genes that usually appears together. Still, this is just one gene among many that may be involved in alcoholism and addiction in general.

The work is significant because it did find that haplotypes seem to predict whether a patient would be diagnosed as dependent or an abuser – a first in alcoholism diagnosis. Further progress in this area might allow medical professionals to predict whether someone will be prone to alcoholism, perhaps allowing intervention even before they are exposed to their first drink. It also hardens the position of treating alcoholism as a disease. With the advent of cheap genetic testing, markers that can warn us, even in childhood, about dangerous possibilities are becoming more common. Even now, you can get your genome tested for $100 dollars from private gene testing companies. While they do not offer to test for this trait yet, they do test for a hundred others.

Identifying specific receptors also gives drug companies a target for medications. Along with testing, we can expect further advances from this type of research that will have real world applications.

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