Scientists have found a biological clue that could help explain why African-Americans appear to be more vulnerable than white Americans to Alzheimer's disease.
A study of 1,255 people, both black and white, found that cerebrospinal fluid from African Americans tended to contain lower levels of a substance associated with Alzheimer's, researchers report Monday in the journal JAMA Neurology.
Yet these low levels did not seem to protect black participants from the disease.
The finding "implies that the biological mechanisms underlying Alzheimer's disease may be very different in [different] racial groups," says Dr. John Morris, an author of the paper and director of the Knight Alzheimer's Disease Research Center at Washington University in St. Louis.
And if Alzheimer's works differently in African-Americans, that difference could make them more vulnerable to the disease, Morris says.
The study has limitations, though, says Lisa Barnes, a cognitive neuropsychologist at the Rush Alzheimer's Disease Center in Chicago, who wrote an accompanying editorial.
For example, it could not fully account for the effects of some other known Alzheimer's risk factors — including hypertension, diabetes and obesity — or some suspected risk factors, including stress and poverty. Also, the study included just 173 African-Americans, and was able to obtain spinal fluid samples from only half of them.
Even so, Barnes says she was excited to see the study "because we have so little data" on African-Americans and other racial and ethnic minorities.
At the moment, most of what scientists have learned about Alzheimer's comes from studies of white people.
"We know relatively little about whether Alzheimer's disease is manifested in an identical way in underrepresented groups," Morris says.
So researchers at Washington University have spent the past two decades reaching out to the African-American community in St. Louis. For example, the Alzheimer's research center has had an African-American Advisory Board since 2000 to help it be "more welcoming to people of color," Morris says.
The effort made it possible to do the study comparing Alzheimer's in whites and blacks, Morris says. But he adds that getting spinal fluid, which required participants to undergo an uncomfortable procedure was still "not an easy ask."
The study included people ages 43 years old to 104. Most had no signs of memory or cognitive problems, while about a third were in the early stages of dementia.
"We set out to see if the disease process seems to be the same in both racial groups," Morris says.
Researchers used brain scans and samples of spinal fluid to look for two biological hallmarks of Alzheimer's. One was amyloid, a protein that forms sticky plaques in the brain. The other was a protein called tau, which forms toxic tangles inside brain cells.
Blacks and whites in the study were no different when it came to plaques. "However, the tau proteins were notably different," Morris says.
Spinal fluid from African-Americans contained lower levels of tau protein. And the difference was most apparent among those with a gene called APOE4.
Other studies have shown that in white people, having the APOE4 gene variant can triple the risk of developing Alzheimer's. But there is evidence that the allele has a much less dramatic effect in black people.
Morris says it's too soon to speculate about why there may be a link between the APOE4 gene and low tau levels in African-Americans. But if the link is real, he says, it could eventually lead to an explanation for racial differences in Alzheimer's that includes biology.
First, though, researchers would need to confirm the tau connection in a study that includes many more African-Americans, Barnes says.
And that will be a challenge, she says, because African-Americans are often hesitant to participate in medical research, especially if it involves an invasive procedure like a spinal tap.
"When you try to go to populations that have been sort of marginalized and abused by past research," she says, "it becomes very, very difficult."
One way to do bigger studies of African-Americans is for research centers to collaborate. "If we start to pool our numbers together, we'll be able to do more than just one center alone [could do]," Barnes says.
But to truly understand how Alzheimer's disease works in people who aren't white, she says, more researchers will have to reach out to groups that have been wary of scientific studies.
"We really need minority communities to be involved and to have a voice in what we're finding," Barnes says. "We can't do it by ourselves."