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A specific type of protein may cause daytime sleepiness in people with Alzheimer’s, according to a recent study.
Many people with Alzheimer’s disease have a tendency to sleep a lot during the day, even when they have had a full night’s sleep.
Based on links between excessive sleepiness and neurodegenerative conditions, researchers are speculating that looking at daytime napping patterns could help predict the development of Alzheimer’s.
But what remains unclear is why, exactly, people with this condition experience the need to sleep so often.
A new study, conducted by researchers at the University of California, San Francisco (UCSF) and other institutions, shows that people with Alzheimer’s disease experience major brain cell loss in regions of the brain tasked with keeping us awake.
The findings, which appear in the journal Alzheimer’s & Dementia, also suggest that an overaccumulation of tau protein triggers these brain changes.
In Alzheimer’s disease, tau proteins form tangles that disrupt communication between neurons (brain cells) and impact cell health.
“Our work shows definitive evidence that the brain areas promoting wakefulness degenerate due to accumulation of tau — not amyloid protein [another protein that can become toxic in Alzheimer’s disease] — from the very earliest stages of the disease,” explains senior author Dr. Lea Grinberg.
Tau: ‘a direct driver of cognitive decline’?
In the study, Dr. Grinberg and the team analyzed the brains of 13 deceased people who had Alzheimer’s disease, as well as those of seven deceased individuals who had not experienced clinical neurodegeneration. The researchers obtained these samples from UCSF’s Neurodegenerative Disease Brain Bank.
The team found that, in comparison with healthy brains, those affected by Alzheimer’s disease had a high level of tau across three regions that are key to staying awake, namely the locus coeruleus, the lateral hypothalamic area, and the tuberomammillary nucleus. Not only this, but these regions had actually lost 75% of their neurons.
“It’s remarkable because it’s not just a single brain nucleus that’s degenerating, but the whole wakefulness-promoting network,” notes the study’s lead author, Jun Oh.
“Crucially, this means that the brain has no way to compensate because all of these functionally related cell types are being destroyed at the same time,” Oh explains.
For further clarification, the researchers went on to conduct a postmortem analysis of brain samples from seven people who had progressive supranuclear palsy and corticobasal disease. These are two forms of dementia that are characterized specifically by the overaccumulation of tau protein.
In these samples, the scientists did not find the same loss of neurons in areas connected with states of wakefulness, which suggests that this destructive loss may only occur in Alzheimer’s disease.
“It seems that the wakefulness-promoting network is particularly vulnerable in Alzheimer’s disease. Understanding why this is the case is something we need to follow up in future research,” says Oh.
Previous evidence uncovered by Dr. Grinberg and colleagues also suggests that tau protein may have a direct impact on brain degeneration in Alzheimer’s disease. In that study, the team found that people who died with high levels of tau in their brain stem — which corresponds to early stage Alzheimer’s disease — had begun to develop mood changes and sleep problems.
“Our new evidence for tau-linked degeneration of the brain’s wakefulness centers provides a compelling neurobiological explanation for those findings,” says Dr. Grinberg.
“It suggests we need to be much more focused on understanding the early stages of tau accumulation in these brain areas in our ongoing search for Alzheimer’s treatments,” she adds.
“This research adds to a growing body of work showing that tau burden is likely a direct driver of cognitive decline.”
Dr. Lea Grinberg
Frontotemporal dementia: What’s to know?
Frontotemporal dementia is a type of dementia that tends to start at a younger age than other types. Symptoms include changes in behavior and personality and a decline in thinking and coordination. It is thought to happen as parts of the brain shrink over time. Antidepressants and memory aids may help people cope.
What are the signs of early-onset Alzheimer’s?
Early-onset Alzheimer’s disease is a form of dementia that begins before the age of 65. Recognizing the initial symptoms can help a person seek treatment earlier and slow the progression of the disease. In this article, learn about ten signs of early-onset Alzheimer’s. We also cover how to help a loved one cope.
What is the difference between dementia and Alzheimer’s?
Dementia is an umbrella term that describes symptoms affecting memory and cognitive function. Alzheimer’s disease is a specific, and the most common, type of dementia. The conditions overlap in terms of symptoms, but Alzheimer’s has different and specific treatments as well as unique symptoms. Learn more here.
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