Brain protein indicates a link between circadian rhythm dysfunction and Alzheimer's Disease Fractured sleep, daytime sleepiness and other signs of disturbance in one's circadian rhythm are common complaints of people with Alzheimer's disease, and the problems only get worse as the disease progresses. But the reason for the link between Alzheimer's and circadian dysfunction is not well understood. Researchers at Washington University School of Medicine in St. Louis say that a clue may lie in the brain protein YKL-40. In a study published Dec. 16 in Science Translational Medicine, the researchers report that YKL-40 is both regulated by clock genes and involved in clearing away potentially toxic buildup of Alzheimer's proteins in the brain. Moreover, Alzheimer's patients who carry a genetic variant that reduces YKL-40 levels maintain their cognitive faculties longer than people without the variant, the scientists found.