Asthma, an inflammatory breathing disorder, affects more than 300 million people worldwide, and African Americans are a disproportionately large part of that number. Now scientists have discovered a possible reason why: a genetic mutation found exclusively in black folks, according to a study published in the journal Nature Genetics and reported by Reuters.

For the study, researchers evaluated 15,000 asthma cases from nine different studies organized to search for asthma-associated genes in ethnically diverse North American population groups. (The groups included European Americans, African Americans, Hispanics and Mexicans.)

After completing study evaluations, researchers reported they’d found four genes seen in previous, smaller studies, plus a fifth gene, common only in people of African descent. “This is the first discovery of a gene where we see a signal in African Americans only,” said lead study author Dan Nicolae, PhD, at the University of Chicago.

The rates of asthma in different ethnic groups are different, but no one knows why African Americans’ asthma rates are increasing, Nicolae said. He suggested that although this increase may be due to changing environmental risk factors, the new findings suggest genetics may contribute significantly.

While scientists cautioned they aren’t exactly sure how this one mutation increases asthma risk, and they point out that biological risks are multiplied when combined with environmental factors, they are excited about what this additional research might find.

The scientists planned to explore how genetics and environmental risk factors, such as smoking, affect asthma and how to better treat the condition.

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