Reduced hypocretin (orexin) levels in dementia with Lewy bodies.

Sleep disorders are observed in Parkinson's disease, dementia with Lewy bodies, and Alzheimer's disease; however, the underlying mechanisms are unclear. Reduced hypocretin (orexin) levels are reported in Parkinson's disease and sleep disorders, including narcolepsy; however, its levels in dementia with Lewy bodies and Alzheimer's disease and its relationship with sleep disturbances in these disorders remain undetermined. We examined hypocretin levels in dementia with Lewy bodies and Alzheimer's disease cases and correlated these with sleep habits and clinical characteristics. Although limited hypocretin alterations were observed in Alzheimer's disease, we show reduced neocortical hypocretin immunoreactivity in dementia with Lewy bodies patients correlating with hypersomnolence and alpha-synuclein levels. These results suggest the involvement of hypocretin in sleep disorders in dementia with Lewy bodies.