Frequency of mixed neuropathologies in individuals with down syndrome with and without Alzheimer's dementia.

Individuals with Down syndrome (DS) develop Alzheimer's disease neuropathological change (ADNC) by the age of 40 years, and most develop dementia by their early 50s. The frequency of co-pathologies in clinically and neuropathologically characterized adults with DS has not been systematically characterized. We characterized the frequency of ADNC and common co-pathologies, including cerebral amyloid angiopathy (CAA), Lewy pathology (LP), limbic predominant age-related TDP-43 encephalopathy neuropathological change (LATE-NC), hippocampal sclerosis (HS), and other cerebrovascular and macroscopic findings reported in standardized National Alzheimer's Coordinating Center (NACC) neuropathology forms in 63 adults with DS over 40 years. A secondary exploratory objective was to compare the neuropathological profiles between individuals with (n = 55) and without (n = 8) dementia from the same autopsy cohort. In the full autopsy cohort, cortical and hippocampal atrophy, and moderate-to-severe locus coeruleus hypopigmentation was a common finding. Pure ADNC, was present in only 29% of individuals. CAA was the most frequent co-pathology, present in approximately 84% of individuals followed by LP (21%), HS (19%), and LATE-NC (17%). Atherosclerosis and arteriolosclerosis were infrequent. In exploratory comparisons between dementia groups, brain weight was significantly lower in individuals with dementia than in those without (900 ± 116 vs 1060 ± 108 g P = .0006), and severe hippocampal atrophy and locus coeruleus hypopigmentation were more frequent in those with dementia (P = .049, P = .009, respectively). Advanced Braak NFT stage, frequent neuritic plaques, and high ADNC were more frequent in individuals with dementia (P = .0001, P = .03, P = .0016, respectively). LATE-NC and HS occurred exclusively in individuals with dementia, while LP and CAA were found in both groups. Individuals without dementia showed a less complex co-pathology profile than those with dementia. Our findings demonstrate that co-pathologies are present in people with DS, and that despite their genetic predisposition to AD, some individuals with DS may exhibit resilience and resistance mechanisms to AD.