To what degree is late life cognitive decline driven by age-related neuropathologies?

The aging brain is vulnerable to a wide array of neuropathologies. Prior work estimated that the three most studied of these, Alzheimer’s disease (AD), infarcts, and Lewy bodies, account for about 40% of the variation in late life cognitive decline. However, that estimate did not incorporate many other diseases that are now recognized as potent drivers of cognitive decline (e.g. limbic predominant age-related TDP-43 encephalopathy [LATE-NC], hippocampal sclerosis, other cerebrovascular conditions). We examined the degree to which person-specific cognitive decline in old age is driven by a wide array of neuropathologies. 1,164 deceased participants from two longitudinal clinical-pathologic studies, the Rush Memory and Aging Project and Religious Orders Study, completed up to 24 annual evaluations including 17 cognitive performance tests and underwent brain autopsy. Neuropathologic examinations provided 11 pathologic indices, including markers of AD, non-AD neurodegenerative diseases (i.e. LATE-NC, hippocampal sclerosis, Lewy bodies), and cerebrovascular conditions (i.e. macroscopic infarcts, microinfarcts, cerebral amyloid angiopathy, atherosclerosis, and arteriolosclerosis). Mixed effects models examined the linear relation of pathologic indices with global cognitive decline, and random change point models examined the relation of the pathologic indices with the onset of terminal decline and rates of preterminal and terminal decline. Cognition declined an average of about 0.10 unit per year (estimate = -0.101, SE = 0.003, p < 0.001) with considerable heterogeneity in rates of decline (variance estimate for the person-specific slope of decline was 0.0094, p < 0.001). When considered separately, 10 of the 11 pathologic indices were associated with faster decline and accounted for between 2 and 34% of the variation in decline, respectively. When considered simultaneously, the 11 pathologic indices together accounted for a total of 43% of the variation in decline; AD-related indices accounted for 30–36% of the variation, non-AD neurodegenerative indices 4–10%, and cerebrovascular indices 3–8%. Finally, the 11 pathologic indices combined accounted for less than a third of the variation in the onset of terminal decline (28%) and rates of preterminal (32%) and terminal decline (19%). Although age-related neuropathologies account for a large proportion of the variation in late life cognitive decline, considerable variation remains unexplained even after considering a wide array of neuropathologies. These findings highlight the complexity of cognitive aging and have important implications for the ongoing effort to develop effective therapeutics and identify novel treatment targets.