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 tau associated with Alzheimer's, researchers report in the journal JAMA Neurology. Yet these low levels did not seem to protect black participants from the disease.
 
There were no racial differences in the frequency of cerebral ischemic lesions noted on results of brain magnetic resonance imaging, mean cortical standardized uptake value ratios for r for amyloid-β42 concentrations in CSF. However, in individuals with a reported family history of dementia, total hippocampal volumes were lower for African American participants than for white participants. CSF concentrations of total tau were lower in African American participants than in white participants  as were mean concentrations of phosphorylated tau₁₈₁ . There was a significant race by APOE ε4interaction for both CSF total tau and phosphorylated tau₁₈₁ such that only APOE ε4–positive participants showed the racial differences.
 
The finding "implies that the biological mechanisms underlying Alzheimer's disease may be very different in [different] racial groups," says an author of the paper.
 
And if Alzheimer's works differently in African-Americans, that difference could make them more vulnerable to the disease, the author says.

The study has limitations, though, says  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.
 
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," the author says.
 
https://www.npr.org/sections/health-shots/2019/01/07/682036486/study-suggests-alzheimer-s-disease-may-work-differently-in-african-americans

https://jamanetwork.com/journals/jamaneurology/article-abstract/2719700