Friday, March 21, 2008

Genetics' Role in Health Disparities

Continued from page 1

By Emily Singer

TR: Are existing genomic studies biased?

CR: Yes. The overwhelming number of major genetic studies done have been done in Europeans. But a center like this will help us change that dynamic by helping to set up a large cohort of African-American and African populations.

TR: Why is it so important to study genetic variations and disease in different populations?

CR: In the context of common complex diseases such as hypertension, diabetes, and heart disease, genes are usually not enough, and environmental factors [are] also not enough to cause disease. It is the combination of both. Gene-environment interaction is particularly important when making comparisons between populations. The underlying genetic variant might be the same in both groups, but environmental factors [may change its impact]. For example, let's say gene A is related to hypertension because it responds to a high-salt diet. If the frequency of this genetic variant is about the same in both African Americans and European Americans, but African Americans eat more salt, they will be more likely to develop hypertension and therefore have higher rates of the disease.

TR: One area of great controversy in race-based medicine was over Bidil, a heart-failure drug and the first pharmaceutical targeted exclusively at a specific racial group--in this case, African Americans. What do you see as the problem with Bidil?

CR: The irony of Bidil is that it was not based on genetic studies. The study did not look at any specific gene in this group called African Americans. It's important for us to be able to understand the genetics behind these issues. Then we can ask, who among the African-American and the European populations has this variation, and thus the ability to respond to a particular drug, or the potential to suffer an adverse side effect? It would no longer be an issue of group identity.

Part of the point I have been trying to make is that we can get jaded in our own thinking and in the ways we design scientific studies. For example, it's important when comparing African Americans to their European-American counterparts that we take a critical look at what is going on in West Africa--the ancestral source populations of African Americans. Most African Americans share a considerable proportion of their gene pool with West Africans--greater than 80 percent. So before ascribing a genetic explanation to group differences, it is important to understand what is going on in the source population. For example, the rate of hypertension is about 7 percent in most of rural West Africa, about 16 percent in the urban centers, about 26 percent in the black nations of the Caribbean, and 35 percent among African Americans. This data clearly shows the importance of current environment in the prevalence of hypertension in these populations that share very recent ancestry.

TR: What are you working on now?

CR: One of the most exciting things we're working on is using the Affymetrix 6.0 chip [a gene chip that can simultaneously detect close to one million specific genetic variations] to study more than 2,000 African Americans from the Washington, DC, area. We've collected the data and will begin the analysis soon; if no one beats us to it, this will be the first genome-wide association study in an African-American cohort. We are searching for genes linked to hypertension and obesity, and may look for diabetes-linked genes in the future.

We have also been studying the genetics of diabetes in Nigeria, Kenya, and Ghana, and are planning to expand that cohort to have a sufficient number of participants to do genome-wide association studies.