Sleep disorders and Alzheimer’s disease may be more closely linked than previously thought - a new study suggests that people who carry a genetic susceptibility to Alzheimer’s disease may be at greater risk for cognitive problems from certain sleep disorders, such as sleep apnea. This shows a shared genetic connection between the two diseases, which may lead to more effective ways to treat both.

The genetic allele ε-4 (APOE-ε4), is associated with increased Alzheimer’s disease risk, but according to the new research, it appears to increase incidence of cognitive problems in people with certain breathing problems connected to poor sleep. Specifically, sleep apnea was associated with worse attention and mental processing speed, and these associations were strongest among the genetic allele carriers.   

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About 20 percent of the population is believed to carry the allele. These findings are significant as "previous studies have shown inconsistent findings between sleep-disordered breathing and cognition,” said lead study author Dayna A. Johnson in a statement, although she explained that this may have been due to different tests used.  

The study also found that having an oxygen saturation below 90 percent during sleep, a condition known as increased overnight hypoxemia, was associated with poorer attention and memory. In addition, daytime sleepiness was associated with poorer attention and memory and slower processing speed.

"Our study provides further evidence that sleep-disordered breathing negatively affects attention, processing speed and memory, which are robust predictors of cognitive decline," added senior study author Susan Redline, in a statement.

For the study, the team looked at 1,752 volunteers with an average age of 68 who were participants in the Multi-Ethnic Study of Atherosclerosis (MESA). The volunteers underwent an in-home sleep study as well as a number of tests to measure their brain function. Adjustments were made for race, age, body mass income, education levels, smoking status, hypertension, diabetes, benzodiazepine use, and depressive symptoms.

Sleep apnea is a common sleep disorder that causes more shallow or even stopped breathing while sleeping, the National Institutes of Health reported. These pauses can occur 30 times of more an hour and can cause the sleeper to make either snoring or choking noises as they slumber. Importantly, most people with this condition do not know it, and it is usually family members that notice the sleep disruptions. The condition is more common in overweight individuals.

Alzheimer’s disease is a type of dementia associated with a number of memory, thinking, and behavior problems, the Alzheimer’s Association reported. An estimated 5 million Americans are believed to be living with this disease.

The team hope their findings can be used to develop a more effective way to diagnosis Alzheimer's disease in aging populations.

"Given the lack of effective treatment for Alzheimer's disease, our results support the potential for sleep-disordered breathing screening and treatment as part of a strategy to reduce dementia risk," said Redline.

Source: Johnson DA, Lane J, Wang R, et al. Greater Cognitive Deficits with Sleep-Disordered Breathing among Individuals with Genetic Susceptibility to Alzheimer’s Disease: the Multi-Ethnic Study of Atherosclerosis. Annals of the American Thoracic Society. 2017

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