Article Abstract:
A study by Blum et al. in the May 1990 issue of The Journal of the American Medical Association reported that the prevalence of a variant of the gene for the D2 dopamine receptor, the A1 allele, was significantly greater among alcoholics than among nonalcoholics. This finding ignited much controversy and skepticism, and studies since that time have produced conflicting results. One problem with all of these studies has been a small sample size. In the October 2, 1991 issue of The Journal of the American Medical Association, two more studies on this issue are reported. The study by Comings et al. reported findings from several large populations, that the A1 allele was more prevalent among alcoholics than normal subjects. However, the prevalence rate was less than 50 percent in alcoholics and they concluded that the presence of this allele was not a cause of alcoholism, but rather a modifier of the expression of alcoholism. In the study by Gelernter et al., no significant difference was found in the prevalence of the A1 allele between alcoholics and nonalcoholics. When results from the six studies on this issue are combined, the prevalence of the A1 allele in alcoholics is seen to be certainly higher than that in control subjects. It would thus appear that the A1 allele contributes to alcoholic behavior, but does not cause it. This is the first instance that a genetic link to a common psychiatric disorder has been discovered. Further studies with larger populations are needed to find the exact prevalence of the allele and the clinical use of such knowledge. (Consumer Summary produced by Reliance Medical Information, Inc.)
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Article Abstract:
Dopamine is a chemical substance that plays an important role in the transmission of certain nerve signals to and from the brain. Abnormalities of the D2 dopamine receptors have been suggested as a cause or a partial cause of some neurological and psychiatric disorders. Previous researchers have reported that a variation of the D2 dopamine receptor gene (DRD2) known as the A1 allele was present at a significantly higher rate in alcoholics than in nonalcoholics. Other studies have reported similar findings, while yet others have reported no association between the A1 allele and alcoholism. To further examine this issue, the allele at the DRD2 gene locus was determined in 44 alcoholics and 68 control subjects. All subjects were white and none were biologically related. The A1 allele was found in 35 percent of the control subjects and in 45 percent of the alcoholic subjects. Differences between alcoholics and controls in overall frequencies of the A1 and A2 alleles at DRD2 were not considered statistically significant. When the subjects in the alcoholic group were further subdivided into groups based on family history of alcoholism, age at onset, and consumption, the prevalence of the A1 allele was not significantly different for any of these subgroups compared with that of the control group. It is concluded that there is no association between the A1 allele of the DRD2 and alcoholism. (Consumer Summary produced by Reliance Medical Information, Inc.)
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Article Abstract:
Accumulated evidence on the relation between the A1 allele at the D2 dopamine receptor (DRD2) gene and alcoholism remains inconclusive. A 1990 study found that carriers of the A1 allele at DRD2 had a significant risk of alcoholism. Since then, several studies on the A1 allele at DRD2 have been conducted, some of which support an association with alcoholism and some of which refute it. In a review of data from all studies on the A1 allele at DRD2 and alcoholism, there was no significant difference in the frequency of A1 between alcoholics and non-alcoholics. Furthermore, heterogeneity was greater within the groups of alcoholics and non-alcoholics than between the groups. Frequency of the A1 allele varies among different ethnic groups. All studies that limited participants - alcoholics and non-alcoholics - to one ethnic group found no differences in A1 frequency between the two groups. These findings suggest that heterogeneity within the groups and ethnicity may explain the association between the A1 allele and alcoholism found in some studies.
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