In a research first, Alzheimer’s-like amyloid plaques have been found in the brains of people with clinically verified obstructive sleep apnea, according to the results of a small study published last week in the journal Sleep.

Sleep apnea and Alzheimer’s are thought to be related, but the reasons for the connection remains unclear, the researchers said. In the new study, plaques were found to develop in the same place (the hippocampus) and spread in the same way in the brains of people with obstructive sleep apnea as they do in Alzheimer’s. In addition, the severity of sleep apnea was linked with greater plaque build-up.

Notably, the use of continuous positive airway pressure (the standard treatment for moderate to severe sleep apnea) made no difference in the amount of plaques found, reported Stephen Robinson, Ph.D., of RMIT University, Melbourne, Australia.

The study participants had no clinical symptoms of dementia before they died. This suggests that they may have been in an early pre-dementia stage of disease, the authors concluded.

“While some people may have had mild cognitive impairment or undiagnosed dementia, none had symptoms that were strong enough for an official diagnosis, even though some had a density of plaques and tangles that were sufficiently high to qualify as Alzheimer’s disease,” Robinson said.

The authors hope to conduct a larger clinical trial of the study, and plan to further analyze the current samples for additional understanding of how the participants’ brains had changed.