Weighting and standardization of frequencies to determine prevalence of AD imaging biomarkers

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Objective:

To estimate the prevalence of elevated brain amyloid and reduced cortical thickness (as a marker for neurodegeneration) in a defined population.

Methods:

Mayo Clinic Study of Aging participants underwent MRI to assess a composite Alzheimer disease (AD) signature cortical thickness measure and PET to assess brain amyloid accumulation. Participants were characterized as having elevated amyloid (A+/A–), reduced cortical thickness (N+/N–), and A+N+, A+N–, A–N+, or A–N–. The prevalence of AD biomarkers was derived by adjusting for nonparticipation and standardizing to the Olmsted County, Minnesota, population.

Results:

Among 1,646 participants without dementia (mean age 70.8 years; 53.2% men), the prevalence (95% confidence interval) of amyloidosis was 21.1% (19.1%–23.2%): women, 24.3%; men, 17.5%. The prevalence of reduced cortical thickness was 28.9% (26.4%–31.5%): women, 27.9%; men, 30.2%. The prevalence estimates of biomarker categories were as follows: A–N–: 61.4%; A+N–: 9.7%; A–N+: 17.4%; and A+N+: 11.5%, and varied by sex and by APOE 4 carrier status. In men, prevalence estimates were as follows: A–N–: 62.6%; A+N–: 7.3%; A–N+: 19.9%; and A+N+: 10.2%. In women, prevalence estimates were as follows: A–N–: 60.4%; A+N–: 11.7%; A–N+: 15.3%; and A+N+: 12.6%. In 4 carriers, prevalence estimates were as follows: A–N–: 54.6%; A+N–: 16.6%; A–N+: 12.4%; and A+N+: 16.4%. In non-4 carriers, prevalence estimates were as follows: A–N–: 63.3%; A+N–: 6.9%; A–N+: 19.9%; and A+N+: 10.0%.

Conclusions:

These prevalence estimates are important for understanding age-related trends in amyloid positivity and AD signature cortical thickness in the population, and for potentially projecting the future burden of biomarkers in elderly persons.

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