Editors' ChoiceAlzheimer’s Disease

Big dipper, little dipper

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Science Translational Medicine  25 Nov 2015:
Vol. 7, Issue 315, pp. 315ec202
DOI: 10.1126/scitranslmed.aad5912

Blood pressure typically dips at night—a sign of a healthy, reactive vasculature. “Nondippers,” individuals with similar daytime and nighttime blood pressure, have a higher risk of cardio- and cerebrovascular disease. Because such vascular risk factors increase the risk of Alzheimer’s disease, Tarumi and colleagues examined whether compromised vascular reactivity might underlie this relationship.

The authors tested the association between nondipper status and amyloid deposition (a hallmark of Alzheimer’s disease) in individuals with amnestic mild cognitive impairment (usually a result of Alzheimer’s disease pathology). Participants who showed less than a 10% drop in blood pressure at night were considered nondippers. These people had increased amyloid deposition in the posterior cingulate region, as measured by 18F-florbetapir PET. A more precise gauge of cerebral vasculature reactivity (cerebral blood flow measurement with transcranial Doppler during a sit-stand maneuver) confirmed that reactivity was impaired in the nondippers. Furthermore, in the entire study cohort, decreased cerebral blood flow reactivity was associated with increased amyloid deposition in the posterior cingulate region.

Limitations of the study include the small sample size (40) and the fact that the authors did not test for obstructive sleep apnea, which is associated with both nondipper status and with Alzheimer’s disease. Additionally, mean arterial pressure, not systolic pressure, determines cerebral blood flow; therefore, the study would have been more compelling if mean arterial pressure had been analyzed.

This study raises the interesting possibility that correcting unhealthy vascular function in patients who show early and preclinical Alzheimer’s disease, when amyloid plaque burden is increasing, may alter the progression from amyloid plaques to symptomatic Alzheimer’s disease.

T. Tarumi et al., Amyloid burden and sleep blood pressure in amnestic mild cognitive impairment. Neurology 10.1212/WNL.0000000000002167 (2015). [Abstract ]

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