β-Amyloid Burden Predicts Lower Extremity Performance Decline in Cognitively Unimpaired Older Adults.
BACKGROUND
Motor slowing is associated with risk of Alzheimer's disease. Whether β-amyloid (Aβ) burden is associated with motor decline, independent of cognitive decline, is unknown.


METHODS
About 59 cognitively unimpaired older participants had baseline PET-PiB scans and repeated measures of lower (usual gait speed, 400-m time, Health ABC Physical Performance Battery (HABCPPB) score, total standing balance time) and upper (mean tapping time) extremity performance during a mean follow-up of 4.7 years. Linear mixed effect models examined the relationship between baseline Aβ burden and motor decline, adjusting for age, sex, body mass index, cardiovascular risk, APOE ɛ4 status, memory decline, depressive symptoms, ankle-arm index, processing speed, executive function, and cerebrovascular disease.


RESULTS
Higher mean cortical Aβ burden was associated with greater declines in gait speed and HABCPPB score and a greater increase in 400-m time. Higher Aβ of putamen was associated with declines in all lower extremity measures, including balance. Higher Aβ of dorsolateral prefrontal cortex and lateral temporal lobe was associated with declines of gait speed and 400-m time, and of precuneus with a greater increase in 400-m time. Associations remained similar after further adjustment.


CONCLUSIONS
In cognitively unimpaired older adults, Aβ burden overall and in specific brain regions are risk factors for lower extremity motor decline, independent of memory function. These findings provide the first empirical evidence that Aβ burden is a risk factor for mobility decline in older adults.
Longitudinal Studies Section, Translational Gerontology Branch and.
Qu
Q
Tian
Laboratory of Behavioral Neuroscience, National Institute on Aging, Baltimore, Maryland.
Susan M
SM
Resnick
Laboratory of Behavioral Neuroscience, National Institute on Aging, Baltimore, Maryland.|Department of Biomedical Engineering, School of Medicine, Johns Hopkins University, Baltimore, Maryland.
Murat
M
Bilgel
Department of Radiology, Section of High Resolution Brain Imaging.|Department of Psychiatry.|Department of Neuroscience.|Department of Neurology, and.|Department of Environmental Health Sciences, Johns Hopkins Medical Institutions, Baltimore, Maryland.
Dean F
DF
Wong
Longitudinal Studies Section, Translational Gerontology Branch and.
Luigi
L
Ferrucci
Longitudinal Studies Section, Translational Gerontology Branch and.
Stephanie A
SA
Studenski
D000368:Aged; D000369:Aged, 80 and over; D016229:Amyloid beta-Peptides / Q000378:metabolism*; D005260:Female; D015577:Geriatric Assessment; D006801:Humans; D035002:Lower Extremity / Q000503:physiopathology*; D008297:Male; D008875:Middle Aged; D049268:Positron-Emission Tomography; D012307:Risk Factors
D016229:Amyloid beta-Peptides
Epidemiology; Gait; Neuroimaging
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