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Genetic analysis explores the influence of African ancestry in brain disease risk

AILSA CHANG, HOST:

Brain disorders like Alzheimer's disease and stroke are more common in Black Americans than in white Americans. At the same time, Parkinson's disease is less common. NPR's Jon Hamilton reports on a new genetic analysis that could help explain why.

JON HAMILTON, BYLINE: Black Americans have been underrepresented in most genetic studies. So a team of researchers in Baltimore did one that included only individuals who identified as Black or African American. Kynon Jade Benjamin is a scientist at the Lieber Institute for Brain Development at Johns Hopkins University. He says the team wanted to answer a question about brain disorders.

KYNON JADE BENJAMIN: Can we tease apart anything that might be influenced by our ancestry - our genetic ancestry?

HAMILTON: To find out, the team studied cadaver brain tissue from 151 people whose next-of-kin agreed to the research. Most Black Americans have a mix of African and European genetic ancestry. Benjamin says that allowed the team to see how each of these two ancestries affected the brain.

BENJAMIN: We leverage the history of the U.S. to pinpoint, in just a Black population, how European ancestry versus African ancestry affects gene expression in the brain.

HAMILTON: Gene expression describes which genes are turned on or off in a cell. And Benjamin says a person's ancestry was most likely to influence the gene expression in immune cells.

BENJAMIN: Even though we're looking in the brain, we're seeing immune - an immune response as the things that are - seemed to be affected by genetic ancestry.

HAMILTON: Ancestry also affected gene expression in cells that line blood vessels, which might explain differences in the risk for stroke. But it did not affect neurons, the brain cells thought to play a key role in psychiatric disorders like schizophrenia. So at least in this study, ancestry did not explain why schizophrenia is diagnosed more frequently in Black Americans than white Americans. The finding with immune cells could help explain why Black Americans are more vulnerable to Alzheimer's, while their white counterparts are more likely to get Parkinson's. Benjamin says in those disorders, certain genes are more likely to be switched on or upregulated.

BENJAMIN: For, like, Parkinson's, we saw an upregulation in European ancestry. While when we looked at stroke and Alzheimer's, we saw that upregulation in the genes associated with African ancestry.

HAMILTON: Overall, inherited differences explained about 60% of the changes in gene expression. Environmental factors such as nutrition and mental stress appeared to explain another 15%. Benjamin says the study, published in the journal Nature Neuroscience, suggests that doctors need to look beyond race when assessing a person's risk for a specific disease.

BENJAMIN: If a patient comes with some kind of particular symptoms, don't rule it out just because somebody is African American 'cause at that particular gene, they could be European.

HAMILTON: The study also shows why genetic research needs to be more diverse. Dr. Kafui Dzirasa is a researcher and psychiatrist at Duke University.

KAFUI DZIRASA: This study is really important because it demonstrates, clearly, scientifically, the imperative for advancing science in a way that works for everybody.

HAMILTON: Dzirasa says understanding how ancestry can protect someone from a disease could lead to new and better treatments. He says race is a social construct, not a biological one, so it's a highly imperfect way of assessing someone's ancestry. Even so, he still notes how his patients identify, for now.

DZIRASA: The more optimal future is one in which we understand each person's individual genomic architecture and then prescribe medicines based on this.

HAMILTON: Which is the goal of an emerging approach known as precision medicine. Jon Hamilton, NPR News.

(SOUNDBITE OF KENDRICK LAMAR SONG, "SING ABOUT ME, I'M DYING OF THIRST") Transcript provided by NPR, Copyright NPR.

NPR transcripts are created on a rush deadline by an NPR contractor. This text may not be in its final form and may be updated or revised in the future. Accuracy and availability may vary. The authoritative record of NPR’s programming is the audio record.

Jon Hamilton is a correspondent for NPR's Science Desk. Currently he focuses on neuroscience and health risks.