CHICAGO, Jan. 7 (Xinhua) -- A study from Washington University School of Medicine in St. Louis suggests that Alzheimer's disease may be under-recognized in African-Americans as researchers at the university have identified racial disparities between African-Americans and Caucasians in the level of a key biomarker used to identify Alzheimer's disease.
African-Americans typically have lower levels of the brain protein tau, which means they might not meet the threshold to be diagnosed when Alzheimer's disease already has begun to develop in their brains.
For this study, the researchers analyzed biological data from 1,215 people, of whom 14 percent or 173 were African-American. The participants averaged 71 years of age. Two-thirds showed no signs of memory loss or confusion, and the remaining one-third had either very mild or mild Alzheimer's dementia. All participants underwent at least one test for Alzheimer's: a PET scan to detect plaques of toxic amyloid protein in the brain, an MRI scan for signs of brain shrinkage and damage, or a spinal tap to measure levels of key Alzheimer's proteins in the fluid that surrounds the brain and spinal cord.
Analysis of the MRI and PET scans showed no significant differences between African-Americans and whites. But when the researchers examined the samples of cerebrospinal fluid, they discovered that African-Americans had significantly lower levels of the brain protein tau.
Elevated tau has been linked to brain damage, memory loss and confusion, but having lower levels of tau didn't protect African-Americans from those problems. They were just as likely as Caucasians to be cognitively impaired in the study.
"With tau, the pattern was the same in African-Americans and whites - the higher your tau level, the more likely you were cognitively impaired - but the absolute amounts were consistently lower in African-Americans," said John C. Morris, a professor of neurology at the university. "What this may indicate is that the cutoffs between normal and high levels of tau that were developed by studying whites are probably not accurate for African-Americans and could cause us to miss signs of disease in some people."
This difference was most significant in people with the high-risk form of the gene APOE, known as APOE4. Older Caucasians who carry the APOE4 gene variant have a threefold increase in risk of developing Alzheimer's disease, making it the single strongest genetic risk factor in that group. But previous studies have found that the gene variant has a much weaker effect in African-Americans.
When the researchers broke down their data by APOE status, they found that African-Americans with the high-risk form of the gene had lower levels of tau than Caucasians who also carried the risky variant. But among people who carried the low-risk forms of the gene, tau levels were similar, regardless of race.
"It looks like the APOE4 risk factor doesn't operate the same in African-Americans as it does in whites," Morris said. "We need to start looking into the possibility that the disease develops in distinct ways in various populations. People may be getting the same illness - Alzheimer's disease - via different biological pathways."
A more complete understanding of the ways Alzheimer's can arise could open up new avenues of research to prevent or treat the devastating disease, the researchers stated.
The findings were published Monday in JAMA Neurology.
