Study: Social factors may surpass genetics in assessing stroke risk

March April
(Fly View Productions/E+ via Getty Images)

While genetic and social factors are known to influence stroke risk, a recent studyfound a surprising variance based on where people live. Genetic scoring only identifies higher stroke risk for people living in the most privileged neighborhoods. In less financially secure neighborhoods, its predictive usefulness declines and disappears.

Researchers looked at acute ischemic stroke, the most common type of stroke. It’s caused by a clot blocking blood flow to the brain. Genetic factors are known to influence stroke risk, and previous research shows the risk also can be affected by poverty, low education or lack of health insurance, factors known as social determinants of health.

Researchers used data from more than 147,000 people and 787 neighborhoods in the analysis. Participants were part of the National Institutes of Health's All of Us research program, which emphasizes groups underrepresented in medical research, such as people with low incomes and those living in rural areas. Among them, 3,201 had strokes.

To assess the participants' genetic risk, the researchers used a polygenic risk score for stroke. The score was based on 530 genetic variants related to blood pressure, cholesterol, blood glucose, body mass index, diet, physical activity and the likelihood of smoking.

To assess neighborhoods, they used the Census Bureau's American Community Survey, which has data on income, education, poverty level and more, broken down by ZIP code. The researchers split those ZIP codes into three categories: low, intermediate or high deprivation.

When genetics and neighborhoods were analyzed together, the link between the polygenic risk score and stroke risk was significant in the least-deprived neighborhoods. There, a higher genetic risk score can increase a person's stroke risk by about 10%.

But in a surprise to researchers, the increased risk from a higher genetic risk score was statistically insignificant for the middle group of neighborhoods. And it vanished in the most-deprived neighborhoods.

"The polygenic risk score has basically no effect on the risk of ischemic stroke for the people living in these highly deprived neighborhoods," said lead author Dr. Cyprien Rivier, a postdoctoral research fellow at Yale School of Medicine in New Haven, Connecticut.

The findings suggest that genetic risk can be modified by where you live, Rivier said. But the study was not designed to explain why.

"This is the big question," he said, "and this is also where we should be careful not to make conclusions based on these results." It's possible, he said, that burdens on people who live in deprived areas overshadow their genetic risks.

Social epidemiologist Anusha M. Vable, an assistant professor at the University of California, San Francisco, said the research suggests that in the most-deprived neighborhoods, the baseline level of risk was so high that those who were not genetically susceptible to acute ischemic stroke had the same risk as those who were.

To her, that suggests social determinants of health matter more than genetic susceptibility for having an acute ischemic stroke. "And I think that's actually really good news," she said, because social determinants of health can be improved by strengthening social safety net policies. There is no such fix for genes.