Evidence for a Genetic Component for Substance Dependence in Native Americans

Objective

Although tribes differ with regard to the use of alcohol and drugs, substance dependence is one of the primary sources of health problems facing Native Americans. General population studies have demonstrated that substance dependence has a substantially heritable component (approximately 50% of the risk resulting from genetic influences); however, fewer studies have investigated the role of genetics in the risk for substance dependence in Native Americans.

Method

The authors present a literature review of the evidence for a genetic component in the etiology of substance dependence in Native Americans, including studies of heritability, linkage analyses, and candidate genes.

Results

Evidence for the heritability of alcohol and drug dependence was found. Linkage analyses revealed that genes influencing risk for substance dependence and related phenotypes, such as body mass index (BMI), drug tolerance, EEG patterns, and externalizing traits, reside on several chromosome regions identified in other population samples. Overlap in the gene locations for substance dependence and BMI suggests that a common genetic substrate may exist for disorders of consumption. Studies of the genes that code for alcohol-metabolizing enzymes have not revealed any risk variants specific to Native American populations, although most Native Americans lack protective variants seen in other populations. Other candidate genes associated with substance dependence phenotypes in Native Americans include OPRM1, CRN1, COMT, GABRA2, MAOA, and HTR3-B.

Conclusions

Substance dependence has a substantial genetic component in Native Americans, similar in magnitude to that reported for other populations. The high rates of substance dependence seen in some tribes is likely a combination of a lack of genetic protective factors (metabolizing enzyme variants) combined with genetically mediated risk factors (externalizing traits, consumption drive, and drug sensitivity or tolerance) that combine with key environmental factors (trauma exposure, early age at onset of use, and environmental hardship) to produce an elevated risk for the disorder.