Brain Amyloid-β and Slow Gait in Older Adults without Dementia: Influence of Cognition and APOE-ε4 Genotype

Motor slowing appears in preclinical Alzheimer disease (AD), progresses with AD progression, and is associated with AD pathologic findings at autopsy. Whether amyloid-β (Aβ) is associated with gait speed in elderly individuals without dementia and whether cognition and apolipoprotein E ε4 (APOE ε4) influence this association remain unknown.To examine the association between Aβ and gait speed in elderly individuals without dementia and to study the influence of cognition and APOE ε4 status on this association.This cross-sectional analysis included 183 elderly individuals without dementia, including a cognitively normal (CN) subsample of 144 adults, enrolled in the Ginkgo Evaluation of Memory study at a university center from January 1, 2000, through December 31, 2009, and enrolled in a follow-up substudy a mean (SD) of 10 (3) months after the initial study closeout. Data analysis was performed from October 1, 2015, to June 1, 2016.We assessed cerebral Aβ on Pittsburgh Compound B (PiB) positron emission tomography, gait speed over 4.57 m (15 ft), and cognition on the Mini-Mental State Examination and Trail Making Test Parts A and B. We grouped participants into high Aβ (PiB+) and low Aβ (PiB-) groups on standardized global PiB cutoffs and examined group differences. We studied the influence of cognition and APOE ε4 on the global and regional associations between gait speed and Aβ in the whole sample and the CN subsample.Among the 183 study participants, mean (SD) age was 85.5 (3) years, 76 were women (41.5%), and 177 were white (96.7%). The PiB+ individuals were comparable to the PiB- individuals on demographics, comorbidities, cognition, hippocampal volume, and small-vessel disease but not on gait speed (0.85 vs 0.92 m/s, P = .01) or proportion of APOE ε4 carriers (29 [29.0%] vs 5 [6.0%], P .001). In the whole sample and the CN subsample, the association between global PiB retention and slower gait withstood adjustment for covariates (β = -0.068, P = .03 and β = -0.074, P = .04, respectively); however, this association was attenuated by Mini-Mental State Examination and Trail Making Test Parts A and B and was rendered statistically nonsignificant by APOE ε4 in both samples (β = -0.055 and β = -0.058, respectively; both P ≥ .10). Several regional associations between gait speed and PiB uptake withstood relevant adjustments; however, APOE ε4 rendered only the medial (β = -0.22, P = .03) and lateral (β = -0.08, P = .03) temporal regions, subcortical white matter (β = -0.13, P = .02), and occipital regions (β = -0.15, P = .03) in the whole sample and the occipital regions (β = -0.21, P = .01) in the CN subsample statistically significant.Cerebral Aβ deposition is associated with slower gait speed in elderly individuals without dementia; however, this association is weaker in those who are CN. Cognition and APOE ε4 carrier status influence the association between Aβ and gait speed in elderly individuals without dementia.