Variations in ADH and ALDH in Southwest California Indians

Alcohol Research & Health, Wntr, 2007 by Cindy L. Ehlers

Native Americans as a group have the highest rates of alcohol-related deaths of all ethnicities in the United States; however, it remains unclear how and why a greater proportion of individuals in some Native American communities develop alcohol-related problems and alcohol use disorders (AUDs). One potential factor that can influence responses to alcohol are variations in alcohol-metabolizing enzymes. Researchers have analyzed the frequencies of variants in the alcohol-metabolizing enzymes alcohol dehydrogenase (ADH) and aldehyde dehydrogenase (ALDH) in some Native American populations. So far the studies have yielded no evidence that an ALDH2 variant, which has shown protective effects in other populations, is found in either American Indians or Alaska Natives. A variant of the ALDH1 enzyme that is encoded by the ALDH1A1*2 allele, however, was found in a small proportion of a group of Southwest California Indians and had a protective effect against alcoholism in that population. Furthermore, a variant of the ADH1B enzyme that is encoded by the ADH1B*3 allele was found in a similar proportion of Southwest California Indians and also was associated with a protective effect. However, these findings do not explain the high prevalence of alcoholism in the tribes investigated. KEY WORDS: Alcohol use disorder; alcohol and other drug (AOD)-related (AODR) mortality; AOD use, abuse, and dependence; alcoholism; East Indians; Native American; Southwest California Indians; genetic factors; genetic polymorphisms; protective factors; alcohol flush reaction; ethanol metabolism; alcohol dehydrogenase (ADH); aldehyde dehydrogenase (ALDH); acetaldehyde; ALDH1; ALDH2; ALDH2*2; ALDH1A1*2; ADH1B; ADH1B*3

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Native Americans (i.e., American Indians and Alaska Natives) historically have experienced numerous alcohol-related problems since the drug's introduction into their culture by European settlers. When investigating alcohol use and related problems among Native Americans, however, it is important to recognize the wide diversity among this population's subgroups. Although Native American people comprise less than 1 percent of the U.S. population, there are more than 300 Federally recognized tribes distributed throughout the country. Consistent with this cultural and geographic diversity, policies regarding alcohol use and the prevalence of drinking differ among tribal nations. Some tribes have disallowed alcohol use on their reservations, others are geographically isolated from sources of alcohol, and still others have no formal policy.

Although tribes differ with regard to alcohol use, Native Americans as a group have the highest rates of alcohol-related deaths of all ethnicities in the United States. Indian Health Service reports of age-adjusted death rates attributed to alcohol are more than five times higher than those for the general U.S. population (Shalala et al. 1999). Moreover, although alcohol consumption has taken a greater toll on Native American men than on women, alcohol-related death rates in Native American women still are 3 to 10 times higher, depending on age, than in women in the general population. Despite the devastating impact that alcohol has had on some tribes, however, it remains unclear how and why a greater proportion of individuals in some Native American communities develop alcohol-related problems and alcohol use disorders (AUDs).

Over the years, several popular theories and myths have arisen concerning alcohol use and its consequences in Native American communities. One of these is the "firewater" myth--a common stereotype suggesting that "Indians can't hold their liquor" because their bodies metabolize alcohol differently. Despite the perpetuation of this myth, few studies have tested this hypothesis experimentally. This article explores to what extent the presence of certain variants of alcohol-metabolizing enzymes may, or may not, account for the high rates of alcohol use and AUDs in a select group of Indians residing in southwestern California (Mission Indians), for whom high rates of alcohol dependence have been reported (i.e., up to 72 percent for men and 53 percent for women) (Ehlers et al. 2004a,b; Wall et al. 2003) and who have been studied intensively.

ALCOHOL-METABOLIZING ENZYMES IN NATIVE AMERICANS

As described in other articles in this issue, genetically influenced metabolic factors have been implicated in the etiology of alcoholism not only in Native Americans but also in other ethnic groups. The two main enzymes involved in alcohol metabolism are alcohol dehydrogenase (ADH) and aldehyde dehydrogenase (ALDH). ADH breaks down alcohol to the toxic metabolite acetaldehyde, which is then broken down further by ALDH into the less toxic acetate. There are two main types of ALDH:

* ALDH1, which is found in the fluid filling the cells (i.e., the cytosol), is produced in both the central nervous system and other tissues; in addition to participating in acetaldehyde metabolism, this enzyme is involved in the synthesis of retinoic acid, a precursor of vitamin A.