Identical signs of brain damage in sleep apnea and Alzheimer's
10 October, 2020
A fresh study confirms links between obstructive sleep apnea and Alzheimer’s disease. Possible known reasons for the association are the build-up of toxic products because of lack of oxygen.
In obstructive sleep apnea, a person’s breathing repeatedly stops and restarts. Medical indications include loud snoring, restless sleep, and sleepiness during the day.
Estimates of the condition’s prevalence among adults in the general population vary widely, from 9-38%. However, sleep apnea is normally more prevalent among males, the elderly, and individuals with obesity.
Sleep apnea has links to poor attention, memory, and executive skills, and is an established risk factor for the development of dementia.
“We know that when you have sleep apnea in mid-life, you’re much more likely to build up Alzheimer’s when you’re older and when you have Alzheimer’s, you will have sleep apnea than other persons your actual age,” says Prof. Stephen Robinson of the institution of Health insurance and Biomedical Sciences at RMIT University in Bundoora, Australia.
“The connection is there, but untangling the complexities and biological mechanisms remains an enormous challenge,” he adds.
By studying postmortem samples from people who had sleep apnea, Prof. Robinson and his colleagues recently learned that the severe nature of the problem correlates with reductions in the volume of the hippocampus.
This section of the brain, which is closely involved with memory, also atrophies in persons with Alzheimer’s.
Using the same brain samples, Prof. Robinson’s team has now found the first evidence of amyloid plaques associated with sleep apnea.
Hallmarks of Alzheimer’s
Amyloid plaques certainly are a hallmark of the damage observed in Alzheimer’s, together with clumps of fibers known as neurofibrillary tangles.
The researchers learned that the plaques appear first in the same spots and spread in the same way in the brains of folks with sleep apnea because they do in persons with Alzheimer’s.
Furthermore, the extent of the plaques correlated with the severity of sleep apnea.
“It’s an essential advance in our knowledge of the links between these conditions and opens up new directions for researchers striving to build up therapies for treating and hopefully protecting against Alzheimer’s disease,” says Prof. Robinson, who led the study.
The authors published the analysis, that was a collaboration between RMIT University and the National University Hospital of Iceland in Reykjavik, in the journal Sleep.
The scientists investigated preserved brain samples from 34 persons with a mean age of 67 years who had received a diagnosis of obstructive sleep apnea. Brainstems were designed for study from 24 of these individuals.
None of the patients had received a diagnosis of dementia during their lifetimes. However, 70% had neurofibrillary tangles and 38% had amyloid plaques within their hippocampi.
“While some people may experienced mild cognitive impairment or undiagnosed dementia, none had symptoms which were strong enough for the official diagnosis, despite the fact that some had a density of plaques and tangles which were sufficiently high to qualify as Alzheimer’s disease,” says Prof. Robinson.
Correlation in the hippocampus
After adjusting for factors such as for example age, body mass index (BMI), and sex, the researchers discovered that severity of sleep apnea a person experienced significantly correlated with the quantity of amyloid plaque within their hippocampus.
Sleep apnea correlated less well with the number of neurofibrillary tangles within their hippocampus, and there is no significant correlation after adjusting for age.
When examining the brainstem samples, the researchers found that although about two-thirds contained tangles and a fifth contained amyloid plaques, their amounts did not correlate with the severity of sleep apnea.
In Alzheimer’s disease, plaques and tangles first come in a cortical area near to the hippocampus called the parahippocampal gyrus. The lesions then progress to the hippocampus, before spreading to all of those other cortex.
The same pattern of progression appears to occur in sleep apnea.
“In cases of mild sleep apnea, we're able to only find plaques and tangles in the cortical area near to the hippocampus, precisely where they are first within Alzheimer’s disease,” says Prof. Robinson.
Source: www.medicalnewstoday.com
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