Genetics: Ethnicity

Ethnicity is a term used for categorizing the highly diverse human populations into more homogeneous and distinct ethnic groups, based on their common ancestry and cultural characteristics. An ethnic group is defined as a category of people that, in a larger population, is set apart (to some extent) and bound together (through preferential intermarriage) by common ties of race, language, nationality, or culture. Commonly recognized American ethnic groups include American Indians; Latinos; Chinese; African Americans ("blacks"); and Italians, Irish, and other European Americans ("whites"). Ethnic classifications are rather arbitrary—they change over time ("today's ethnicities are yesterday's races"), and they are different in different countries. For example, a person of Pakistani origin is considered black or colored in the United Kingdom, but would be classified as white or Asian in the United States. Despite obvious limitations, ethnic classification is useful in aging studies because it allows researchers to explore ethnic differences in aging, longevity, and age-related diseases, as well as the possible role of genetic factors in those differences.

Ethnic groups differ significantly in terms of incidence rates and mortality rates from age-related degenerative diseases, including different types of cancer. For example, black Americans have a three-times higher risk of developing esophageal cancer; twice the risk of developing multiple myeloma, liver, cervical, and stomach cancer; and a 50 percent higher risk for cancers of the oral cavity and pharynx, larynx, lung, prostate, and pancreas. In contrast, white Americans have higher incidence rates for melanoma, leukemia, lymphoma, and cancers of the endometrium, thyroid, bladder (in males), ovary, testes, and brain, as well as postmenopausal breast cancer. These ethnic differences are attributed to interactions between genetic and lifestyle factors, such as genetic susceptibility to carcinogens (different in different ethnic groups) and ethnic variations in exposure to certain pollutants. In the case of Ashkenazi Jews, a specific mutation (185delAG) has been found in this ethnic group that increases twenty-seven-fold the risk of early-onset breast cancer in females (1 percent of this ethnic group carries the mutation).

Significant ethnic differences are found for apolipoprotein-E genetic polymorphisms, which are important determinants of blood-lipid levels, atherosclerosis, and longevity. Specifically, the epsilon 4 allele for this apolipoprotein (ApoE4) is more prevalent in African Americans (21 percent) than in non-Hispanic whites (12 percent) or Hispanics (14 percent). The frequency of this allele is inversely correlated with human longevity, and persons with ApoE4 have a doubled risk of Alzheimer's disease.

Sensational reports have often been published in newspapers and magazines claiming an unusually high percentage of centenarians in some exotic ethnic group, remote geographic area, or isolated religious community. The most famous claims of unusual longevity were made for the Vilcabamba population in Ecuador; for remote Caucasus and Altay populations in the former Soviet Union; and for the Old Order Amish religious communities. Later studies found that these claims were either unsubstantiated or even incorrect because of systematic age exaggeration. Thus, the relationship between ethnicity and exceptional longevity remains to be thoroughly studied. It is interesting to note that the highest scientifically validated longevity world records (122 years and 117 years) belong to women of French ethnicity.