Patterns of Mixed Pathologies in Down Syndrome.

Background: Down syndrome (DS) is frequently associated with Alzheimer's disease (AD)-related neuropathological changes. There are few observations on the spectrum of mixed proteinopathies in DS patients.

Objective: This study aimed to evaluate multiple disease-associated proteinopathies in a series of DS cases.

Methods: We analyzed the distribution of neurodegenerative disease associated proteins in postmortem brain samples from 11 DS cases (6 females, median age 57, range 38-66 years). Sections were stained for phosphorylated tau, 3-repeat and 4-repeat tau, amyloid-β, alpha synuclein, phosphorylated TDP-43, and p62. A comprehensive anatomical mapping and staging were applied for all proteins.

Results: Tau and amyloid-β pathology was prevalent in all cases and compatible with that typically seen in AD with some subtle deviations. Four of 11 cases presented with Lewy-related pathology (LRP). Two cases followed the Braak staging (stage 4 and 5) whereas 2 cases presented with an atypical distribution. Two cases showed limbic predominant age-related TDP-43 encephalopathy (LATE) (stage 1 and stage 2) neuropathologic change. Two cases exhibited aging-related tau astrogliopathy (ARTAG).

Conclusion: In addition to subtle deviations from AD regarding the morphology of amyloid-β deposition and distribution of neuronal tau pathology, we find that the spectrum of mixed-pathologies in DS show distinctive features such as deviations from the Braak staging of LRP and that LATE neuropathologic change and ARTAG pathology can be seen in individuals younger than in sporadic AD cases. Our observations support the notion that DS has distinctive pathogenic pathways from sporadic AD.