It was previously thought the cells were destroyed by a protein called beta-amyloid, but scientists have now concluded the culprit is toxic clumps of protein called tau.
They say the discovery could lead to earlier diagnosis when drugs and lifestyle changes are more likely to work and may also lead to better treatments.
But it was unclear if disturbed sleep put people at risk of Alzheimer’s – or if disease-related brain changes lead to it.
The team at the University of California in San Francisco analysed the brains of 13 deceased patients who had Alzheimer’s disease at the time of death.
They found the three brain areas that boost wakefulness — the locus coeruleus, lateral hypothalamic area and tuberomammillary nucleus — had lost as many as 75 per cent of their neurons.
They also had a significant build-up of tau. The results are significant as they could lead to better treatments by targeting tau instead of beta-amyloid.
It also provides a reason for the regular dozing reported by Alzheimer’s patients and their carers, long before the development of memory problems.
Lead author Dr Jun Oh, based at the Memory and Ageing Centre at UCSF, said: “It is remarkable because it is not just a single brain nucleus that is degenerating, but the whole wakefulness-promoting network.
“Crucially this means the brain has no way to compensate because all of these functionally related cell types are being destroyed at the same time.”
Alzheimer’s can take root up to 20 years before symptoms appear, and it’s believed existing medications are failing because they are given to patients far too late.
What are the warning signs?
Dementia affects 850,000 people in the UK, of which around six in ten have Alzheimer’s. The number will rise to two million by 2050.
In the early stages of disease, the signs may be subtle, mild at first.
But in time they become more pronounced to the point where they begin to interfere with a person’s daily life.
While there are common symptoms, every person diagnosed with Alzheimer’s is unique and is likely to experience the disease differently.
For most, though, the earliest sign are lapses in memory.
As the disease progresses and begins to interfere with a person’s life they may:
- lose common items including keys and glasses around the house
- struggle to find the word they are looking for in conversation
- forget recent conversations or events
- get lost in a familiar place, or while on a familiar journey
- forget important anniversaries, birthdays or appointments
Though memory problems are the most common, there are other signs a person may be struggling with dementia.
- speech problems – a person may struggle to follow a conversation or find they are often repeating themselves
- problems judging distance, navigating stairs or parking the car
- difficulties making decisions and solving problems
- losing track of the day or date
Other signs to watch for include people becoming depressed, irritable and anxious, withdrawn and disinterested in hobbies and other activities they previously enjoyed.
As the disease progresses, a person’s symptoms will become more severe.