Stroke kills about 140,000 people in the United States each year and is a leading cause of long-term disability, according to the Centers for Disease Control and Prevention (CDC).
After heart disease, stroke is the second leading cause of death worldwide.
In the U.S., the risk of having a first stroke is at least 1.6 times as high for Black people as for white people. Black people also have the highest rate of mortality from stroke, out of any ethnic or racial group.
A better understanding of this increased susceptibility can help doctors and health policymakers tackle the underlying causes.
The challenge is complex, however, because stroke is associated with multiple environmental and genetic risk factors.
Scientists have found that genes account for 38% of the risk of having the most common kind of stroke, ischemic stroke. It occurs when the buildup of fatty plaque in the walls of the arteries that supply blood to the brain causes the brain to be starved of oxygen.
However, most previous genetic studies have focused on people of European descent, despite the disproportionate effect that the disease has on people of African ancestry.
Recently, however, an international team of scientists conducted the largest investigation to date into the increased genetic susceptibility of Black people to ischemic stroke.
The researchers identified one particular genetic variant that is significantly associated with stroke among people of African descent, as well as 29 other genetic candidates for increased risk.
“Given the undue burden that people of African ancestry endure from stroke and other cerebrovascular disease, the lack of investigation of risk factors in this group has been a substantial gap,” says Dr. Bradford B. Worrall, a neurologist at the University of Virginia, in Charlottesville, and co-author of the study.
“Our work is an important step toward filling that gap, albeit with much more work to be done. These findings will provide greater insight into ethnic-specific and global risk factors to reduce the second leading cause of death worldwide.”
The scientists have published their research in the journal Stroke.
The work is part of the Consortium of Minority Population Genome-Wide Association Studies of Stroke. For their analysis, the team pooled data from 13 studies, allowing them to compare the genomes of more than 22,000 people of African descent.
Within this group, 3,734 people had experienced an ischemic stroke and 18,317 had not.
The scientists identified a variant in a single genetic letter, or single nucleotide polymorphism (SNP), that was significantly associated with the risk of stroke among Black people.
The variant is close to a gene called HNF1A, which previous research has implicated in lipid metabolism and production of a molecule called C-reactive protein, which is made in the liver in response to inflammation.
Research has also linked HNF1A to the risk of developing diabetes, coronary artery disease, and stroke. The gene, which is particularly active in the liver and pancreas, produces a transcription factor, a protein that helps regulate the activity of other genes.
The researchers found a further 29 SNPs with possible links to stroke in black people, though the evidence for these was less conclusive.
All the SNPs fell within 24 distinct locations within the genome. When the scientists searched other population genome databases, they discovered that 16 of these locations were also linked to stroke risk in people with European and Hispanic ancestry.
The researchers report that, though theirs was the largest investigation into genetic stroke risk among people of African descent, their sample size was still too small to detect rare genetic variants.
However, they say, this highlights the potential for genetic studies involving marginalized populations to provide insights into why some individuals have an increased risk of stroke. As the authors write:
“Our study identified novel associations for stroke that might not otherwise be detected in primarily European cohort studies. Collectively, this highlights the critical nature and importance of genetic studies in a more diverse population with a high stroke burden, such as was the case in this study.”
The authors believe that in the future, studies like theirs will support the development of precision medicines targeted at an individual’s specific genetic vulnerabilities.
Nonetheless, it is important to keep in mind that a substantial proportion of the health disparities among ethnic and racial groups have an environmental, rather than a genetic, origin.
In addition to lifestyle factors, social and economic inequity likely play a significant role in the increased risk of stroke among Black people.
