A large multinational team of genetic researchers has identified three unique genetic variations that influence body size and obesity in men and women of African ancestry.

Obesity is a worldwide health epidemic, associated with higher cardiovascular disease, diabetes and mortality, and lower quality of life. Nearly 50 percent of African-American adults in the United States are clinically obese, compared to 35 percent of non-Hispanic white adults.

The new study, reported in Nature Genetics, is a meta-analysis of 3.2 million genetic variants in over 30,000 people with African heritage for links to body-mass index (BMI). It is the largest study ever done on this population to date.

The study shows that people from different populations share similar genetic traits that impact body size – people with African ancestry shared 32 gene variants previously associated with BMI in European and Asian populations. The study also reveals that people with African ancestry possess three genetic variations (GALNT10, MIR148A-NFE2L3 and KLHL32) that work in concert with environmental factors to impact BMI.

“I would love to stress that this paper is really just a start or a foundation for understanding the role of genetic variation in obesity. We expect obesity to be influenced by hundreds, if not thousands of genes and many, many environmental factors. While some genetic variants are likely to increase or decrease weight in all people, most are likely to influence weight in specific people depending on their genetic background and their unique environmental history including diet, toxic metal exposure, exercise, etc. We will not fully understand the genetics of obesity until we can fully investigate these context-dependent genetic effects,” said co-author Prof Jason Moore from Dartmouth College.

“In African-Americans, genes played a greater role in causing increased BMI than in Caucasians,” said co-author Prof Christopher Amos from the University of Texas MD Anderson Cancer Center. “To date, the effects in both African-American and Caucasian participants are too small to explain much of the genetic variability in obesity rates, and this may be because the variation reflects both genetic and environmental contributions. Since the environmental factors have not been studied, the actual contribution from genetic factors may be greatly underestimated.”

Subsequent research may clarify how much of a role genes play in promoting obesity, and what might be done to reduce its incidence in vulnerable populations.

Unfortunately, obesity is common not only among African-Americans but among Africans as well.

“In Africa, the World Health Organization has predicted several hundred million new cases of obesity by 2020 (from mid 2000s). In our cohort in Ghana, roughly 25-30 percent of women were obese by U.S. criteria. In South Africa it is even worse,” said co-author Prof Scott Williams from Dartmouth College.

“This research has helped to illuminate human evolutionary history and serves to bring disease presentation into an evolutionary perspective,” Prof Williams concluded.

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Bibliographic information: Keri L Monda et al. A meta-analysis identifies new loci associated with body mass index in individuals of African ancestry. Nature Genetics, published online April 14, 2013; doi: 10.1038/ng.2608