Variant-dependent heterogeneity in amyloid ß burden in autosomal dominant Alzheimer's disease: cross-sectional and longitudinal analyses of an observational study.

BACKGROUND: Insights gained from studying individuals with autosomal dominant Alzheimer's disease have broadly influenced mechanistic hypotheses, biomarker development, and clinical trials in both sporadic and dominantly inherited Alzheimer's disease. Although pathogenic variants causing autosomal dominant Alzheimer's disease are highly penetrant, there is substantial heterogeneity in levels of amyloid ß (Aß) between individuals. We aimed to examine whether this heterogeneity is related to disease progression and to investigate the association with mutation location within PSEN1, PSEN2, or APP. METHODS: We did cross-sectional and longitudinal analyses of data from the Dominantly Inherited Alzheimer's Network (DIAN) observational study, which enrols individuals from families affected by autosomal dominant Alzheimer's disease. 340 participants in the DIAN study who were aged 18 years or older, had a history of autosomal dominant Alzheimer's disease in their family, and who were enrolled between September, 2008, and June, 2019, were included in our analysis. 206 participants were carriers of pathogenic mutations in PSEN1, PSEN2, or APP, and 134 were non-carriers. 62 unique pathogenic variants were identified in the cohort and were grouped in two ways. First, we sorted variants in PSEN1, PSEN2, or APP by the affected protein domain. Second, we divided PSEN1 variants according to position before or after codon 200. We examined variant-dependent variability in Aß biomarkers, specifically Pittsburgh-Compound-B PET (PiB-PET) signal, levels of CSF Aß1-42 (Aß42), and levels of Aß1-40 (Aß40). FINDINGS: Cortical and striatal PiB-PET signal showed striking variant-dependent variability using both grouping approaches (p<0·0001), despite similar progression on the clinical dementia rating (p>0·7), and CSF Aß42 levels (codon-based grouping: p=0·49; domain-based grouping: p=0·095). Longitudinal PiB-PET signal also varied across codon-based groups, mirroring cross-sectional analyses. INTERPRETATION: Autosomal dominant Alzheimer's disease pathogenic variants showed highly differential temporal and regional patterns of PiB-PET signal, despite similar functional progression. These findings suggest that although increased PiB-PET signal is generally seen in autosomal dominant Alzheimer's disease, higher levels of PiB-PET signal at an individual level might not reflect more severe or more advanced disease. Our results have high relevance for ongoing clinical trials in autosomal dominant Alzheimer's disease, including those using Aß PET as a surrogate marker of disease progression. Additionally, and pertinent to both sporadic and autosomal dominant Alzheimer's disease, our results suggest that CSF and PET measures of Aß levels are not interchangeable and might reflect different Aß-driven pathobiological processes. FUNDING: National Institute on Aging, Doris Duke Charitable Foundation, German Center for Neurodegenerative Diseases, Japanese Agency for Medical Research and Development.

Examining Cognitive Decline Across Black and White Participants in the Harvard Aging Brain Study.

BACKGROUND: Black Americans are approximately twice as likely to develop dementia as compared to White Americans and the magnitude of this disparity is often attributed to a variety of factors that include psychosocial and vascular risk factors. However, less is known about the potential contribution of Alzheimer's disease pathological differences. OBJECTIVE: To examine potential differences incross-sectional and longitudinal cognitive performance in black and white participants who were clinically normal at baseline. METHODS: 296 participants (48 African-American/black participants) underwent MRI and amyloid PET at baseline. Linear mixed models were used to examine the main effects of race, years of education, reading ability, Framingham Heart Study cardiovascular risk score (FHS-CVD), white matter hyperintensities (WMH), and amyloid (Aß) burden on the Preclinical Alzheimer Cognitive Composite-5 (PACC5). RESULTS: Lower levels of educationalattainment and reading ability were found for blacks compared to whites. By contrast, no differences in FHS-CVD, WMH, or Aß were found by racial group. Baseline differences in PACC5 score were attenuated after adjusting for educationalfactors, vascular factors, and Aß, but remained lower for blacks compared to whites (ß= -0.24, p = 0.014). Further, blacks demonstrated a faster rate of PACC5 decline longitudinally compared to whites (ß â€Š= -0.055, p = 0.025) after adjusting for covariates. CONCLUSION: Accounting for educationalfactors, vascular factors, and Aß burden diminished, but did not eliminate, racial differences in PACC5 performance longitudinally. Understanding potential differences in longitudinal cognitive outcomes by race may be important for upcoming secondary prevention trials.