Aizenstein HJ et al. (2008) Frequent amyloid deposition without significant cognitive impairment among the elderly. Arch Neurol 65: 1509–1517

The relationship between amyloid β (Aβ) deposition and cognitive function is unclear: previous studies have included participants with normal cognition without knowledge of their Aβ deposition status. Researchers at the University of Pittsburgh measured amyloid deposition and cognitive function in clinically unimpaired elderly volunteers. They found that 21% of participants had substantial amyloid deposits, but that these deposits did not influence cognitive ability.

Aizenstein et al. used PET imaging with the marker Pittsburgh compound B (PiB), which binds amyloid deposits, to measure Aβ deposition in 43 volunteers with a mean age of 74.4 years. Of these participants, 9 were classified as amyloid-positive, 29 as amyloid-negative, and 5 as intermediate (within 2.5% of the cut-off point). APOE ε4 allele frequency was significantly lower among amyloid-negative participants (1 of 29) than among the remaining participants (4 of 14). The Aβ deposits in positive volunteers had a similar distribution to those found in patients with Alzheimer disease, but were present in substantially smaller quantities, and were not associated with impairment of cognitive function.

The results suggest that Aβ deposition might precede the development of clinical symptoms of cognitive impairment, a finding that might have implications for the development of antiamyloid therapies. If PiB retention is indeed a predictor of Alzheimer disease, PiB PET might provide an early indication of risk—years in advance of overt symptoms.