Spatial Extent of Amyloid-β Levels and Associations With Tau-PET and Cognition

Question  In 3 cohorts of cognitively unimpaired persons, does spatial distribution (regional vs widespread) of β-amyloid (Aβ) deposition modify associations with Alzheimer disease–related clinical and biological markers?

Findings  In this cohort study of 817 participants that contrasted Aβ-negative participants vs regional participants, those with regional Aβ binding showed proportionately more apolipoprotein E ε4 carriership, reduced cerebrospinal fluid Aβ1-42 levels, and greater longitudinal Aβ-PET binding accumulation. Participants with widespread amyloid binding further exhibited notable cognitive decline and greater cerebrospinal fluid phosphorylated tau₁₈₁ and tau–positron emission tomography binding than others; using visual reads or each cohort’s specified dichotomous threshold for positivity almost all participants deemed Aβ-positive had widespread Aβ deposition.

Meaning  Regional Aβ binding appears to be biologically relevant among individuals without significant tau and related cognitive decline.

Importance  Preventive trials of anti-amyloid agents might preferably recruit persons showing earliest biologically relevant β-amyloid (Aβ) binding on positron emission tomography (PET).

Objective  To investigate the timing at which Aβ-PET binding starts showing associations with other markers of Alzheimer disease.

Design, Setting, and Participants  This longitudinal multicentric cohort study included 3 independent cohorts: Presymptomatic Evaluation of Experimental or Novel Treatments for Alzheimer Disease (PREVENT-AD) (data collected from 2012-2020), Alzheimer Disease Neuroimaging Initiative (ADNI) (data collected from 2005-2019), and Harvard Aging Brain Study (HABS) (data collected from 2011-2019). In a 3-tiered categorization of Aβ-PET binding spatial extent, individuals were assigned as having widespread Aβ deposition if they showed positive signal throughout a designated set of brain regions prone to early Aβ accumulation. Those with binding in some but not all were categorized as having regional deposition, while those who failed to show any criterion Aβ signal were considered Aβ-negative. All participants who were cognitively unimpaired at their first Aβ PET scan.

Main Outcomes and Measures  Differences in cerebrospinal fluid (CSF), genetics, tau-PET burden, and cognitive decline.

Results  A total of 817 participants were included, including 129 from the PREVENT-AD cohort (mean [SD] age, 63.5 [4.7] years; 33 [26%] male; 126 [98%] White), 400 from ADNI (mean [SD] age, 73.6 [5.8] years; 190 [47%] male; 10 [5%] Hispanic, 338 [91%] White), and 288 from HABS (mean [SD] age, 73.7 [6.2] years; 117 [40%] male; 234 [81%] White). Compared with Aβ-negative persons, those with regional Aβ binding showed proportionately more APOE ε4 carriers (18 [64%] vs 22 [27%] in PREVENT-AD and 34 [31%] vs 38 [19%] in ADNI), reduced CSF Aβ1-42 levels (F = 24 and 71), and greater longitudinal Aβ-PET accumulation (significant β = 0.019 to 0.056). Participants with widespread amyloid binding further exhibited notable cognitive decline (significant β = −0.014 to −0.08), greater CSF phosphorylated tau₁₈₁ (F = 5 and 27), and tau-PET binding (all F > 7.55). Using each cohort’s specified dichotomous threshold for Aβ positivity or a visual read classification, most participants (56% to 100%, depending on classification method and cohort) with regional Aβ would have been classified Aβ-negative.

Conclusions and Relevance  Regional Aβ binding appears to be biologically relevant and participants at this stage remain relatively free from CSF phosphorylated tau₁₈₁, tau-PET binding, and related cognitive decline, making them ideal targets for anti-amyloid agents. Most of these individuals would be classified as negative based on classical thresholds of Aβ positivity.