Ancestry Mix May Be One Key To Obesity

"Studies show that women with European-American ancestry have a higher occurrence of osteoporosis than African-American women," says Dr. Mark D. Shriver, assistant professor of anthropology at Penn State. "African-American women have a higher prevalence of obesity, but it appears not to be as dangerous to their health as it is for European-American women."

Although socially many Americans identify with only one racial/ethnic group, U.S. residents are actually highly mixed. All human populations are closely related and there are very few genes that are different between any two populations. Despite this, there are significant health disparities in the United States with historically disadvantaged populations generally suffering higher prevalences of chronic diseases.

Although it is clear to most biomedical researchers that the primary reason for this difference is differences in wealth, power and privilege, there may be some genetic basis for part of the difference and finding these genes might help researchers to better understand the progression of these diseases and potentially lead to new diagnoses and treatments, according to Shriver.

The Penn State scientist has developed a method to estimate the ancestral proportions of individuals, the percentage of genes that are West African, Native American or European. Researchers can then use this information to investigate the relationships between admixture and various diseases.

In the study, the researchers looked at body mass index – a measure of weight and height, resting metabolic rate, fat mass, fat-free mass and bone mineral density in 145 African-American women from Birmingham, Ala., Baltimore and New York City. They also determined West African ancestry proportion for these women. Determination of West African ancestry was done at Penn State, using 18 ancestry-informative genetic markers.

In the July issue of Obesity Research, the researchers report their analysis of the physical traits and the measure of West African ancestry using two statistical methods. The results showed that there is an association between body mass index -- a measure of obesity -- and West African ancestry. One analytical approach suggests there is also an association between fat mass and fat-free mass and West African ancestry, while the association with bone mineral density is less clear.

"These results support the use of ancestry informative markers when studying differences among admixed populations in complex biomedical traits, particularly when exploring genetic factors influencing these differences," says Dr. Jose Fernandez, assistant professor of nutrition, University of Alabama at Birmingham, and lead author of the published study. "The differences in the prevalence of obesity-related phenotypes among African American females and European American Females could be partly due to genetic factors."

The comparison of resting metabolic rate did not show a significant association, but the researchers believe that the sample size was too small to make this an accurate measure.

Previous studies have explored the relationships of risk for systemic lupus erythematosus and genetic admixture and diabetes and genetic admixture.

"This study supports two things. First, that we are a very mixed country and proportional ancestry is a much more realistic and scientific means to study human variation than is categorical race," says Shriver. "Second, that admixture mapping can and should be an important tool to study both the genetic and environmental causes of obesity."

Beside Shriver and Fernandez, the team included T. Mark Basle, Nashua Rafla-Demetrious, Jeanine Albu, Roland L. Weinsier, David B. Allison, University of Alabama at Birmingham; Esteban Parra, Penn State; Barbara Nicklas, Wake Forest University and University of Maryland; Alice S. Ryan, University of Maryland and Paul M McKeigue and Clive L. Hoggart, London School of Hygiene and Tropical Medicine.

The researchers suggest that expanding the study to larger samples, including environmental measures, increasing the number of markers and looking at other admixed populations like the African Caribbeans is necessary.