Most adults with Down syndrome unknowingly experience severe sleep apnea, according to new research published Saturday in the Journal of Clinical Sleep Medicine.

In a study of 16 adults with Down syndrome, 94 percent were found to have obstructive sleep apnea (OSA). Just one of the participants had previously sought medical assistance for the problem.

People who have obstructive sleep apnea experience breathing difficulty in their sleep, which can disrupt rest. The condition can easily go unnoticed in those with Down syndrome because many symptoms of the two conditions overlap including cardiovascular disease, daytime sleepiness and impaired cognitive functioning.

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While it is well-known that people with Down syndrome have a propensity for sleep apnea, the degree of the findings was surprising, researchers said.

“Patients with Down syndrome have a great deal of risk factors for OSA (based on their narrow mid-face, large tongue, floppy muscle tone, tendency towards being overweight and thyroid disease),” said Carole Marcus, an author of the study and a professor of pediatrics at the University of Pennsylvania. “However, the fact that almost all of the subjects studied had OSA was a much higher prevalence than we expected. It was surprising how severe the illness was and how the OSA was unsuspected by their caregivers.”

Sleep data on the study participants with Down syndrome was compared with that of a control group of adults without Down syndrome. Members of the control were found to sleep over an hour more than those with Down syndrome.

Researchers did find a correlation between the presence of obesity and sleeping troubles, suggesting that weight plays a large role in the likelihood of a person with Down syndrome to experience obstructive sleep apnea.