Research has linked a particular sleep disorder called rapid eye movement (REM) sleep behavior disorder with a diagnosis of Parkinson's disease. What characterizes this sleep problem, and can its presence be a good way to predict Parkinson's risk?
Data from the National Institutes of Health (NIH) indicate that every year, approximately 50,000 people in the United States learn that they have Parkinson's disease, a neurological condition that affects a person's motor function and exposes them to other neurodegenerative problems, such as Alzheimer's disease.
Researchers still do not fully understand exactly what causes Parkinson's disease, but they have identified a few risk factors that can predispose a person to develop this condition.
These include a person's age and sex as well as some genetic factors. Still, it remains a challenge to establish early on who is likely to develop Parkinson's disease at some point in their life.
However, a team of researchers from McGill University in Montreal, Canada decided to see if one particular factor — a sleep disorder called REM sleep behavior disorder (RBD) — could be a good predictor of risk.
This sleep problem is called RBD because it occurs during the REM phase of sleep, in which a person's body becomes effectively paralyzed. This inability to move prevents the person from physically acting out any dream that they may be experiencing and thus stops them from potentially harming themselves or others.
People with RBD do not have this paralysis, which means that they end up acting out their dreams without any notion that they are doing so.
As lead author Dr. Ron Postuma and colleagues explain, establishing that this sleep disorder is a good predictor of Parkinson's could, in the future, allow specialists to identify at-risk people and offer them experimental therapies that could delay or prevent the onset of this neurological condition.
Sleep disorder predicts risk
To establish the strength of the connection between the two conditions, the researchers — whose recent findings appear in Brain: A Journal of Neurology — worked with 1,280 people with REM sleep behavior disorder across 24 centers of the International RBD Study Group.
The researchers assessed the participants' motor function, cognitive abilities, and sensory abilities for a number of years. After a 12-year follow-up period, they found that 73.5 percent of the people involved in this study had developed Parkinson's disease.
Moreover, participants who had started experiencing motor function issues in this period had a threefold increase in the risk of developing Parkinson's disease or related conditions, such as dementia with Lewy bodies.
Also at high risk were participants who had developed cognitive impairment or started experiencing problems with their sense of smell.
These findings confirm that the presence of RBD is, indeed, a strong predictor of Parkinson's disease. All the more so, since the researchers conducted the study in centers across North America, Europe, and Asia, which means that the results apply to diverse populations.
A cheaper, quicker form of assessment
Unlike the usual method of assessing the risk of Parkinson's disease, which is called dopamine transporter imaging, the current assessment is inexpensive and easy to apply.
Dopamine transporter imaging, explain Dr. Postuma and colleagues, assesses the integrity of the dopaminergic system, which typically becomes compromised in parkinsonism and Parkinson's disease. However, this test is complex and costly. In contrast, assessing for the risk factors that the current study considers is both quick and cost efficient.
"We confirmed a very high risk of [Parkinson's disease] in people with REM sleep disorder and found several strong predictors of this progression," notes Dr. Postuma.
"As new disease-modifying treatments are being developed for [Parkinson's disease] and related diseases, these patients are ideal candidates for neuroprotective trials."
Dr. Ron Postuma