Race, Genetics and Health Disparities

Editors: Thomas Burcher and Sarah Wallace

What is the Connection Between Ancestry, Race, and Genetics?

Social scientists contend that race is not a valid biological concept, while biologists and population geneticists contend that the human population is structured like a family tree, with separate branches for Africans, Caucasians, East Asians, Pacific Islanders, and American Indians, says Troy Duster, PhD, in his oft-cited 2005 New York Times Editorial.

According to geneticists, our DNA populated the world through major long-range human migrations. Their theory (further explained by Spencer Wells in his book and subsequent filmJourney of Man) suggests that all humans share a common ancestor out of Africa. Scientific studies have backed up this idea; the variation that we see out of Africa is also seen in Africa, according to Feldmen et all (2003), and Africans are as varied genetically within their group as they are to other groups, says Lehrman (2003).

In fact, human beings are 99.9% identical, genetically speaking. Within that 0.1% of DNA are genetic markers that vary greatly among individuals. Recently, researchers have used a public database, the SNP Consortium, to define this 0.1%. They have gathered tens of thousands of single nucleotide polymorphisms (SNPs), separated them by region of origin, and looked for commonalities. Eventually, researchers discovered trends, and we now know that certain patterns of DNA are associated with certain geographic populations. Excoffier (2003) (link not found 2/15/2007) conducted a detailed genetic analysis of more than a thousand human subjects that clustered them into five groups corresponding to major geographical regions.

Because genetic ancestry tests are showing how very admixed the world is, scientists such as Charmaine Royal, PhD, of Howard University, contend that race is no longer a meaningful concept. To her and many of her colleagues, a more correct term to use when referring to groups of people with distinctive phenotypes is “ethnicity” or “ancestral group.”

Can Genetics Be Used to Explain Health Disparities Among the Races?

One word aptly describes the state of contemporary discourse on race, genetics, and health disparities in the United States, says Kreiger (2005): stormy. While it is necessary to take account of the assumptions about race that are generated by our participation in a racially stratified society, it is also necessary to define exactly what we can know about race through the conduct of science, as explained by Holden (2003). Many scientists have asked the question, “Can available statistical adjustment methods lead to valid inferences when race is regarded as an etiologic quantity, rather than a broad indicator of risk factor status?”

Most ethnicity and health research is “black box” epidemiology, says Bhopal (1997)– or epidemiology where the causal mechanism behind an association remains unknown and hidden (“black”) but the inference is that the causal mechanism is within the association (“box”).

As Fine et al contend in their article entitled “The Role of Race and Genetics in Health Research,” genes appear to have no role in existing first-generation health disparities research, which typically relies on self-reported race (defined according to US Census Bureau categories) as collected in retrospective or prospective cohort studies or from administrative databases. Second-generation health disparities research has identified numerous patient, provider, health care system, and environmental factors that are independent of human biology as contributors to health disparities among racial minorities.

The third generation of health disparities research is in the conception phase; to our knowledge, there are no published reports of interventions specifically designed to reduce or eliminate health disparities. Despite the Food and Drug Administration’s approval of race-specific pharmacotherapy to treat heart failure and glaucoma in African Americans, the jury is still out regarding the use of race to individualize medical therapies as a means of reducing health disparities. Cooper and Kaufman (1998) contend that despite the popularity of racial hypotheses, comparative studies based on observations of broad phenotypes—such as high blood pressure, obesity, or glucose intolerance—have little potential to contribute new knowledge.

Should Race Be Used as a Proxy in Medicine?

Investigators agree that among the three types of factors that influence disease prevalence and response to drugs—genetic, environmental, and cultural—genetic factors play the largest role, according to Lagay (2003). However, the specific question many articles debate has to do with the genetic differences that correlate with disease prevalence and drug response distributed across the human population groups we traditionally call “races.” Does knowing a person’s race provide useful information about his or her susceptibility to certain diseases or probable response to drug therapy?

No one disputes that some diseases strike disproportionately in some racial or ethnic groups – thalassemia in people whose ancestors came from the Mediterranean area, sickle cell anemia in people of African origins, for example, argues Constance Holden in her 2003 Science article. Less clear-cut than these single gene disorders – but the subject of increasing research – isthe medical significance of a host of more subtle gene variants that appear in differing frequencies in various populations and that seem to influence a multitude of conditions.

Proponents of using race as a proxy in medicine such as Neil Risch assert that genetic differences and racial classification are strongly associated, and so support the use of race in the design of research and the application of its findings (Risch et al, 2002). Critics cast race as a social construct and counter that putting subjects into racial groups fundamentally misrepresents human genetic variation and hinders research, say Romualdi et al (2002). Several solutions have been offered, such as replacing race with ethnicity or with genetic markers (as detailed in Kevles’ book, The Code of Codes).

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