Black and Hispanic older adults without dementia showed higher levels of tau in memory-related brain regions than non-Hispanic white participants, and that difference was present even before the amyloid plaque buildup usually treated as the opening act of Alzheimer's disease. The finding comes from a team at the USC Mark and Mary Stevens Neuroimaging and Informatics Institute at the Keck School of Medicine of USC, published in Alzheimer's & Dementia: The Journal of the Alzheimer's Association.
Just as notable as the tau differences was what those proteins predicted. The relationship between the brain markers and how well participants performed on memory testing varied from group to group, meaning the same biomarker reading may not carry the same clinical weight in every population. That complicates a central assumption of modern Alzheimer's diagnosis, which increasingly leans on amyloid and tau measures to identify disease before symptoms arrive.
The data came from the Health and Aging Brain Study - Health Disparities, or HABS-HD, one of the largest and most racially and ethnically diverse brain-imaging studies of aging in the United States. Advanced PET scans allowed the researchers to detect abnormal protein accumulation years ahead of any outward symptoms, which is what made the group comparisons possible in the first place.
The broader point the researchers raise is that most Alzheimer's research has been built on non-Hispanic white participants, so patterns established in that group cannot simply be assumed to hold everywhere. For precision medicine to work across communities, they argue, the field needs a clearer picture of how these brain markers behave in diverse populations - including whether current biomarker thresholds are being applied appropriately to everyone.