Some evidence suggests that African Americans are at higher risk of developing Alzheimer's disease than non-Hispanic white Americans, although researchers haven’t determined the reasons why. Now, a study published online in JAMA Neurology on January 7 suggests that it could be because the disease manifests differently in black populations.
A cross-sectional analysis of specific Alzheimer’s disease biomarkers showed that African Americans with the APOE4 gene, which has been associated with an increased risk of Alzheimer's in white populations, have lower levels of one of these biomarkers, suggesting that Alzheimer’s disease pathology may vary between racial groups.
Because African Americans are typically underrepresented in clinical trials, most of the data about Alzheimer’s disease comes from white participants, which makes it difficult to apply the results to other populations.
To find out if racial disparities exist in Alzheimer’s disease, researchers at Washington University School of Medicine in St. Louis analyzed biomarker data from 1,255 adults (707 women and 548 men), including 173 African Americans whose average age was 70, and tracked them from 2004 to 2015.
The researchers conducted a series of tests to detect two biological hallmarks of Alzheimer’s disease: amyloid, a protein that forms sticky plaques in the brain, and tau, a protein that forms tangles inside brain cells.
Participants underwent a positron emission tomography (PET) scan to detect the presence of amyloid and/or an MRI scan to look for brain shrinkage or damage, and/or a lumbar puncture to measure levels of amyloid and tau in the fluid that surrounds the brain and spinal cord.
At the start of the study, two-thirds of participants showed no signs of memory or cognitive problems; a third showed signs of dementia.
MRI and PET scan findings did not show any significant differences in amyloid levels between African Americans and whites. However, among people who had a reported family history of dementia, total hippocampal volumes and tau levels were lower for African American participants than for white participants. The researchers found no racial differences among participants without a family history of dementia.
Increased tau levels have been associated with brain damage, memory loss, and confusion. Yet lower levels of the protein did not appear to correlate with a lower incidence of Alzheimer’s disease and cognitive dysfunction among African Americans. They were just as likely to develop cognitive impairment as the white participants who had higher levels of tau in their spinal fluid.
In the study, African Americans who carried the APOE4 gene had lower levels of tau than their white counterparts who also carried the gene. (The researchers did not observe lower tau levels in African Americans without the APOE4 gene.)
Based on the findings, the researchers hypothesized that APOE4 may be less strongly associated with tau accumulation in African Americans than it is in white populations. Past research, they noted, has found a weaker association between APOE4 and Alzheimer's disease in African Americans.
It's too early to determine if there is a link between the APOE4 gene and lower tau levels in African Americans, the researchers wrote. They urged caution in interpreting the results until larger studies that account for the influence of socioeconomic status, coexisting health problems, and other factors that may contribute to racial differences can confirm or refute them.
But the study highlights racial differences that exist in Alzheimer's pathology, which could pave the way for future diagnostic and therapeutic advances.
