The problem of alcoholism in American Indians has been comprehensively addressed in three family linkage datasets: 1] SW tribe; 2] Eastern Oklahoma tribe with low prevalence of alcoholism; 3] Plains Indian tribe with neuropsychological data [EEG] - analytical studies in progress; and also in a large cross-population study in progress - the Ten Tribes Study which systematically compares 1800 randomly sampled subjects from seven tribes. In addition, LNG is the genetics collaborating laboratory on the first pharmacogenetic study on alcoholism treatment response [to naltrexone and sertraline]. This study, on Alaska Natives, is led by S. O'Malley [Yale]. We are assessing genetic linkage to alcoholism and associated psychiatric disorders in a Southeastern Oklahoma.North American Indian tribe with over 30,000 enrolled members living within tribal boundaries in Oklahoma. Psychiatric assessment was with the SSAGA semi-structured interview. By contrast to neighboring American Indian tribes that have high prevalences of alcoholism, this tribe stands out because alcoholism has a low prevalence, about 1% and 10% of females and males, respectively. By studying American Indians in the context of low alcoholism, we can expect to reveal differences in the roles of genetic and/or environmental determinants of alcoholism. Genetic analysis is being conducted using two samples from the tribe: a small random sample (N=100) and large extended families (N=200 tested subjects). The sampling design accommodates case-control association analyses and non-parametric two- and multi-point linkage methods. In order to perform the analyses outlined above, individual psychiatric interviews and blood samples have been collected. Research diagnoses are made from the psychiatric interviews and DNA for genotyping is being extracted from the blood samples. We are also examining individual differences in cultural experience and how they relate to vulnerability to alcohol related problems. This year we have begun collection of EEG, ERP and heart rate variability data on the individuals we previously interviewed. This project includes population genetics analysis of numbers of alleles, allele frequencies, and haplotype differences among American Indian tribes. This includes studies focused on genes involved in behavior [e.g. COMT] and gene cluster regions [e.g. chr 5 GABAA cluster]. This information is important to genetic linkage and disease association studies on American Indians because failure to account for population diversity can result in false evidence for linkage, and allelic heterogeneity among groups can create spurious associations with disease. The genetic systems being typed are the same as those being used currently in our genetic linkage analyses. We are also able to study comparison populations, including Asians. Some of this work is being carried out in collaboration with Kenneth Kidd, at Yale. Various tests for allele frequency differences between tribal groupings based on cultural and linguistic affinities are being performed. In order to more fully quantify isolate structure, and exploit such populations for linkage analyses, we have developed a maximum likelihood method to characterize populations by their levels of gene identity. We have applied this method to microsatellite typings for three American Indian and three European populations. Low gene identity was observed in Europeans, approximately 28%. By contrast, gene identity was higher in all American Indian populations, about 39%. We have studied local patterns of gene diversity in 7 samples from populations in the Southwest and Alaska. These populations all speak closely related Athabascan languages, despite their dispersed geographic locations. When compared to non-Athabascan speaking neighbors, we do not find a strong tendency for these populations to comprise a unified gene pool. Rather, geographic proximity is the best predictor of the genetic relationship. In American Indians, reduced haplotype diversity was observed at several loci, including DRD2 and ADH. Large differences in the frequencies of several functional alleles as compared to Caucasian populations were detected. These include DRD2 Ser311Cys, COMT Val158Met, and HTTLPR. The whole genome scan for the SW tribe detected two potential new loci for alcoholism: the DRD4 region at the chromosome 11p telomere, and the region of the GABAA cluster near the chromosome 4p centromere. The SW Indian sample is a large family (N=582) comprising a sizeable fraction of a Southwestern tribe with a high rate of alcoholism (85% of males, greater than 50% of females). This family was systematically interviewed, substantial evidence for familial transmission of alcoholism was found, and then it was evaluated for genetic linkage in collaboration with investigators from NIDDK and, using a large (N=517) panel of DNA markers that covered the genome. A similar whole-genome scan is underway in the Plains Indian tribe, where EEG intermediate phenotypes were also collected. Candidate gene linkage findings include two that are anxiety-related: serotonin transporter/anxiety and a sex-specific association of COMT Val158Met to anxiety. The HTR1B gene appears to be linked to antisocial alcoholism. The SW tribe studies were informative for the meaning and consequences of alcohol-related diagnoses in American Indians. The results are representative because 1] the very large family was ascertained solely on the basis of structure and availability, 2] the family is representative of the tribe in coefficient of relationship and demography, and 3] CAGE scores do not differ from a random sample of 3112 individuals studied collaboratively by NIDDK [Hanson et al]. The evidence from the SW tribe is that binge drinking is neither benign nor beneficial, that alcoholism is familial, and that the same patterns of psychiatric comorbidity seen in the general U.S. population [National Comorbidity Survey] are seen in Indian alcoholics. Almost all of the large fraction of the population who were binge drinkers were also alcoholics, and binge drinkers tended to become alcoholic at a younger age. Regardless of whether binge drinkers met criteria for alcoholism, they were dramatically worse off in each of the four symptom categories evaluated in the SADS-L: social, work, violence/lawlessness and physical. We found the same heavy clusterings of psychiatric disorders with alcoholism as previously observed in the general population of the U.S. These results may help lay to rest the misconception that drinking, particularly binge drinking, is other than deleterious to American Indians and regardless of whether binge drinking is culturally determined or congruent.
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