Little-known sleep disorder that's a red flag sign of dementia and Parkinson's

A sleep disorder that is little-known and not fully understood could be a sign of developing Parkinson's or dementia. REM sleep behaviour disorder affects around 1% of the general population, but 2% of people aged over 65.

REM is rapid eye movement - one stage of the sleep cycle. It plays an important role in dreaming, memory, emotional processing and healthy brain development.

It's during this stage of sleep that people enter a state of low muscle tone. That means muscles don't 'act out' dreams, reports the Mirror.

But REM sleep behaviour disorder sees people respond to their dreams - kicking, shouting or screaming during sleep. Patients report being chased or attacked in their dreams and can respond violently.

It can lead to them harming themselves or their partner. Some 60% of patients and 20% of bed partners of people with the disorder have reported injuries during sleep.

The disorder is not fully understood. It can appear at any age, but usually starts for people in their 40s and 50s. For those younger, antidepressants can cause the disorder.

Younger women and men are affected in equal numbers, but for those aged over 50 it tends to affect men more often. It has been associated with neurodegenerative disorders such as Parkinson’s disease and dementia with Lewy bodies - abnormal deposits of a protein called alpha-synuclein in the brain.

Scientists are trying to work out if REM sleep behaviour disorder may foreshadow the diseases. It is seen in 25% to 58% of patients diagnosed with Parkinson’s and 70% to 80% of patients with dementia with Lewy bodies.

In a long-term study looking at 1,280 patients with the disorder, researchers observed participants to see how other issues developed. After 12 years, 73.5% of those with REM sleep behaviour disorder had developed a related neurodegenerative illness.

Other things that were shown to increase the risk of developing a neurodegenerative disorder were irregular motor symptoms, abnormal dopamine levels, loss of sense of smell, cognitive impairment, abnormal colour vision, erectile dysfunction, constipation and older age, reports OregonLive.

RBD may be detectable decades before the symptoms fully develop and early detection would help boffins study the disease. At this time there are few therapies in way of treatment, but melatonin and clonazepam can be used as medicine to improve the symptoms.