People with a rare sleep disorder are more prone to develop dementia or Parkinson's disease, the findings of a new Canadian study suggest.

The so-called rapid eye movement (REM) sleep behavior disorder affects only a small percentage of the population, according to lead researcher Dr. Ronald B. Postuma, at McGill University in Montreal, Quebec. Patients with rapid eye movement behavior disorder (RBD) act out dramatic or violent dreams during rapid eye movement (REM) stage sleep. The condition, which is similar to sleepwalking and periodic limb movement disorder, often affects men aged 50 and more.

Normally, during REM sleep, the muscles relax and don’t move, but people with certain sleep disorders are able to cry out.

Researchers followed 93 patients diagnosed with RBD and examined them after 5, 10 and 12 years for signs of neurological disorders like Parkinson disease (PD) and dementia. The participants were on average 65 years old. At the end of the study, most of those with RBD developed either dementia or Parkinson's. More precisely, there were 26 volunteers who developed a degenerative brain disease: 15 developed Parkinson’s and 11 developed dementia, according to the results, published in the Dec. 24 online issue of the journal Neurology.

"We don't have ways to prevent those diseases now, but maybe that's because by the time a person has these diseases, it's too late to intervene," Postuma said in a press statement.