Genetic Variant Tied to Greater Obesity Risk in African Americans


A slight change in a person’s genes can predispose them toward obesity, shows a new study from researchers at the National Institutes of Health.

Studying obesity in Africans and African Americans, the researchers found that a “genomic variant” in the semaphorin-4D (SEMA4D) gene, which is likely to occur in families, translates to higher weight gain and greater incidence of obesity.

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The variant in the SEMA4D gene is specific to people of African ancestry and does not appear in European or Asian populations, note the researchers. Despite the fact that African Americans have the “highest age-adjusted rates of obesity” in the U.S., much previous research assessing genetic material has focused on people of European ancestry.

“We wanted to close this unacceptable gap in genomics research,” said Dr. Charles Rotimi, director of the Center for Research on Genomics and Global Health (CRGGH) at the National Institutes of Health.

The new focus opens up additional opportunity for understanding — and perhaps preventing — rates of obesity among African Americans.

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“By studying people of West Africa, the ancestral home of most African Americans, and replicating our results in a large group of African Americans, we are providing new insights into biological pathways for obesity that have not been previously explored,” said study co-author Dr. Ayo P. Doumatey, CRGGH staff scientist. “These findings may also help inform how the African environments have shaped individual genomes in the context of obesity risk.”

Researchers found that people with a variant in the SEMA4D gene were an average of six pounds heavier than people without the variant, according to the study appearing in the journal Obesity.

Obesity Overload: Rates Continue to Rise

The researchers believe that a greater understanding of how genes impact a person’s weight will help stem the tide of surging obesity rates. “Most of the world’s population now lives in countries where death due to overweight and obesity is greater than from underweight,” report the authors.

“Eventually, we hope to learn how to better prevent or treat obesity,” Dr. Rotimi said.

While other factors play a key role in weight and obesity, understanding genetic predisposition can serve a critical function. “Despite the great influence of lifestyle and culture on the prevalence of obesity, it is well documented that obesity clusters in families, with heritability estimates as high as 60 percent,” state the authors.

Credit: Sandra Cohen-Rose and Colin Rose/Flickr, CC BY 2.0

The World Health Organization estimates that some 600 million adults around the world are obese, according to 2014 data. What’s more, nearly 2 billion — or nearly 40 percent of the world’s adult population — are considered overweight. In the U.S., two out of three adults are overweight, according to the National Institutes of Health.

Yet high weight isn’t limited to just adults. About 41 million children under the age of five are considered overweight or obese, says the World Health Organization.

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Dr. Rotimi and his colleagues are conducting ongoing investigations into the role of SEMA4D in obesity among African Americans, and they plan “to conduct larger studies of DNA sequencing” to identify other factors that are linked to obesity.

Currently, they know that “SEMA4D has been shown to play a role in cell-cell signaling, immune response, and bone formation,” according to the study in Obesity.

“Furthermore, we observed that circulating SEMA4D levels were considerably higher in individuals with obesity compared with those without obesity,” they conclude.