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Sleep apnea is linked with tau accumulation in the brain



Witnessed apneas during sleep are associated with increased tau accumulation in the entorhinal cortex, according to data that will be presented at the annual meeting of the American Academy of Neurology. Tau accumulation is a biomarker of Alzheimer’s disease, and the finding suggests a possible explanation for the apparent association between sleep disruption and dementia.

“Our research results raise the possibility that sleep apnea affects tau accumulation,” said Diego Z. Carvalho, MD, of the Mayo Clinic in Rochester, Minn., in a press release. “But it is also possible that higher levels of tau in other regions may predispose a person to sleep apnea, so longer studies are now needed to solve this chicken-and-egg problem.”

Previous research had suggested an association between sleep disruption and increased risk of dementia. Obstructive sleep apnea in particular has been associated with this increased risk. The pathological processes that account for this association are unknown, however.

Dr. Carvalho and colleagues decided to evaluate whether apneas during sleep, reported by the patient or an informant, were associated with high levels of tau in cognitively normal elderly individuals. The investigators identified 288 participants in the Mayo Clinic Study of Aging for their analysis. Eligible participants were aged 65 years or older, had no cognitive impairment, had undergone tau PET and amyloid PET scans, and had completed a questionnaire that solicited information about witnessed apneas during sleep (either from patients or bed partners). Dr. Carvalho’s group took the entorhinal cortex as its region of interest because it is highly susceptible to tau accumulation. The entorhinal cortex is involved in memory, navigation, and the perception of time. They chose the cerebellum crus as their reference region.

The investigators created a linear model to evaluate the association between tau in the entorhinal cortex and witnessed apneas. They controlled the data for age, sex, years of education, body mass index, hypertension, hyperlipidemia, diabetes, reduced sleep, excessive daytime sleepiness, and global amyloid.

In all, 43 participants (15%) had witnessed apneas during sleep. Witnessed apneas were significantly associated with tau in the entorhinal cortex. After controlling for potential confounders, Dr. Carvalho and colleagues estimated a 0.049 elevation in the entorhinal cortex tau standardized uptake value ratio (95% confidence interval, 0.011–0.087; P = 0.012).

The study had a relatively small sample size, and its results require validation. Other important limitations include the absence of sleep studies to confirm the presence and severity of sleep apnea and a lack of information about whether participants already were receiving treatment for sleep apnea.

The National Institutes of Health supported the study.

SOURCE: Carvalho D et al. AAN 2019, Abstract P3.6-021.

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