Allele frequencies of the preproenkephalin A (PENK) gene CA repeat in Asians, African-Americans, and Caucasians: lack of evidence for different allele frequencies in alcoholics.
Evidence from animal models and from recent reports on the efficacy of the opioid antagonist naltrexone in the treatment of alcoholism suggests that the endogenous opioid systems may play a role in alcohol seeking behavior. The gene encoding preproenkephalin A (PENK) is flanked at its 3' end by a polymorphic (CA)n repeat. We determined the allele frequencies for this locus in samples of Chinese and Atayal living in Taiwan, Caucasians living in the United States and Byelorussia, and African-Americans living in the United States. We compared the allele frequencies of nonalcoholics in each population with those of alcoholics with or without alcohol-induced organ pathology. There was no difference in allele frequencies within any racial group when alcoholics with or without organ pathology were compared; there was also no difference in allele frequency between nonalcoholics and alcoholics within the two Asian populations, Caucasians, or African-Americans. There were highly significant differences in the frequency of the various length polymorphisms between the Asian, Caucasian, and African-American samples.