Origins of racial health disparities can involve both genes and environment and the interactions between them

Jan 17 2005

New understanding of the dynamic interplay between genes and environment, made possible by technologies arising from the Human Genome Project, helps support the individualization of medicine and makes focusing on racial or ethnic group differences in disease less relevant, say Penn State researchers.

"Technology has given us the ability to make a much more comprehensive picture of health outcomes," says Dr. Keith Whitfield, associate professor of biobehavioral health. "We now see, for example, that the origins of racial health disparities can involve both genes and environment and the interactions between them. The crux of the matter is the individual, with her or his unique genetic constitution and history of environmental influences."

Whitfield and Dr. Gerald McClearn, Evan Pugh professor of health and human development, are the authors of a paper, "Genes, Environment, and Race," published in the current issue of American Psychologist. The January issue is a special issue devoted to race in health and social science research.

The researchers write, "Investigations of the origins of health disparities across ethnic groups have traditionally emphasized environmental hypotheses that concentrate on social and economic inequities related to differential health outcomes. The recent explosion of genetic research clearly shows how genes affect individual variation in many aspects of health and illness."

They point out that some diseases, such as phenylketonuria or Huntington's chorea, have been found to be associated with a single major gene. However, they note, that one gene/one disease scenarios are typically not the case. Rather, because of gene/gene and gene/environment interactions, a particular genetic input or particular environmental input may have quite different consequences in different individuals. In addition, although one gene might be regarded as "the" gene for a condition, it is not necessarily "the only" gene for the condition.

In addition, Whitfield and McClearn offer the case of African American high blood pressure as an example of how the relative inputs of genetics and the environment to a disease state can vary across cultures. High blood pressure affects about 65 percent of African American elders between the ages of 65 and 74. When the Penn State researchers analyzed data from a recent twin study, the Carolina African American Twin Study of Aging, they found a large proportion of the individual variability in blood pressure for African American adults arose from environmental sources. Previous studies on other populations had shown that, although environment does impact blood pressure, genetic factors played a larger role in determining the individual differences in blood pressure.

In addition, they note that population differences can and do exist with respect not only between majority and minority populations but also among groups of different European origin. As an example, they describe research conducted by McClearn, Whitfield and colleagues with Swedish and Russian twins that showed that the proportion of variance for one particular condition attributable to genetic factors was greater for the Swedish than for the Russian sample. In addition, shared environmental influences were not important in the Swedish sample but accounted for nearly half of the variance in the Russian sample.

Whitfield notes that thanks to progress in genetics, the focus in medicine may return to treating each person as a unique individual. He says, "When doctors knew you and your family and your work and home environment, they were able to treat and prescribe for you based on their awareness of those unique characteristics. Advances in genetics can help return to a more individualized approach to medicine."

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