Direct Relationship Seen Between Plasma Aβ Levels and Cognitive Decline

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Pam Harrison (Medscape Today)

There is a direct and linear association between plasma beta-amyloid (Aβ) levels and multiple aspects of cognitive decline over time, including cognitive changes that constitute conversion to Alzheimer's disease, according to new findings from a population-based, ethnically diverse longitudinal sample of older adults.

Stephanie Cosentino, PhD, from the Taub Institute for Research in Alzheimer's Disease and the Aging Brain at Columbia University Medical Center, New York City, and multicenter colleagues found that in their overall sample of 880 adults, individuals in the top 3 quartiles of Aβ42 at baseline had faster declines in cognitive function during 4.5 years of follow-up than those in the lowest quartile. The same observation held largely true for individuals who remained cognitively healthy during the same study interval.

"Individuals in the top 3 Aβ40 quartiles also declined faster than those in the lowest quartile," investigators add, "[whereas] in the healthy elderly individuals, only the highest quartile declined faster than those in the lowest."

Looking at the rate of global cognitive change by change in Aβ, investigators noted that in both the overall cohort and the healthy elderly, individuals with relatively stable or decreasing Aβ42 values had faster cognitive decline than those with increasing Aβ42 values.

In contrast, change in Aβ40 was not associated with cognitive change in either the overall cohort or the healthy elderly.

"What we tend to see in healthy elders is a steady increase in Aβ42 levels over time, so what we are trying to characterize here is the absence of an increase," Dr. Cosentino told Medscape Medical News.

She also noted that previous studies have shown that high initial plasma levels of Aβ and declining levels of Aβ over time are risk factors for Alzheimer's disease, "so changes in Aβ levels provide information about disease risk." In this particular study, changes in the same plasma Aβ levels predicted the rate of cognitive decline in patients who eventually developed dementia.

"This linear association between plasma Aβ and cognitive change increases our ability to use plasma Aβ as a marker of impending cognitive decline and Alzheimer's disease," Dr. Cosentino said, adding that interestingly enough, the same Aβ profile predicted cognitive decline even in those individuals who remained healthy over time.

The study was published online August 9 and will appear in the December issue of the Archives of Neurology.

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