Brain Scan Marker Helps Classify Alzheimer’s Risk todayheadline

Researchers have identified a brain imaging benchmark that could improve how doctors classify Alzheimer’s disease risk, particularly in Hispanic and non-Hispanic white populations.

The study, involving 675 older adults, established a specific threshold for tau protein accumulation that distinguishes between people with normal cognition and those showing signs of cognitive impairment linked to Alzheimer’s disease.

The findings, published in Imaging Neuroscience, represent a crucial step toward standardizing how brain scans are interpreted across diverse populations. Using an advanced imaging technique called tau PET, scientists can now visualize abnormal tau proteins that contribute to Alzheimer’s disease by injecting a small amount of radioactive tracer that highlights areas where these damaging proteins have accumulated.

Precision in the Brain’s Memory Center

The research team focused on the medial temporal lobe, a brain region deep within the memory center that includes areas crucial for forming and storing memories. When tau protein levels in this region exceeded a specific threshold—measured as a standardized uptake value ratio of 1.26—it strongly indicated cognitive impairment related to Alzheimer’s disease.

“Our tau cut-point was able to distinguish whether study participants had cognitive impairment – but only when another abnormal protein, amyloid, was also present in those with cognitive impairment, and only in Hispanic and non-Hispanic White participants,” explained senior author Meredith N. Braskie, assistant professor of neurology at USC’s Keck School of Medicine.

The study used a newer imaging tracer called 18F-PI-2620, which offers advantages over earlier tau tracers by reducing interference from off-target binding in brain structures like the choroid plexus. This improved precision allows researchers to more accurately measure tau accumulation in the specific brain regions most affected by Alzheimer’s disease.

Key Research Findings:

• The medial temporal lobe threshold of 1.26 effectively identified cognitive impairment in Hispanic and white participants
• The marker performed poorly in non-Hispanic Black participants, suggesting other pathways may drive cognitive decline
• Tau protein accumulation proved most reliable when amyloid plaques were also present
• The technique showed 93% specificity and 75% sensitivity for detecting Alzheimer’s-related cognitive changes

However, the marker showed troubling limitations. In non-Hispanic Black participants, the tau threshold failed to reliably predict cognitive impairment, highlighting a critical gap in current diagnostic approaches.

“In non-Hispanic Black participants, the tau cut-point did not perform as expected. This suggests that other pathologies or conditions may be driving cognitive decline in this group,” Braskie noted, emphasizing the need for more inclusive research approaches.

Diverse Populations, Different Patterns

The study’s most significant contribution lies in its diverse participant base—186 Hispanic, 209 non-Hispanic Black, and 280 non-Hispanic white adults with an average age of 64. This represents a departure from traditional Alzheimer’s research, which has historically focused on predominantly white populations.

Lead author Victoria Tennant, a PhD candidate in USC’s Neuroscience Graduate Program, emphasized the implications: “While our findings support prior research linking medial temporal lobe tau to cognitive impairment, establishing a cut-point in this region using 18F-PI-2620, marks an important step toward defining tau positivity for both research and clinical applications.”

The research reveals that Alzheimer’s disease progression follows different patterns across ethnic groups. The team discovered that 73% of Hispanic participants with mild cognitive impairment were amyloid-negative, compared to 51% of non-Hispanic white participants—suggesting that non-amyloid pathways may play larger roles in cognitive decline among certain populations.

These findings could reshape how clinical trials are designed and how doctors interpret brain scans in diverse patient populations. The work forms part of the Health and Aging Brain Study–Health Disparities, the most comprehensive study of Alzheimer’s disease in diverse communities, which has already produced key findings about ethnic variations in disease biomarkers and social determinants of cognitive health.

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