Biomarkers of Alzheimer disease (AD) pathology can predict the development of dementia with Lewy bodies (DLB) in people with idiopathic REM sleep behaviour disorder (iRBD), new research has shown. Levels of amyloid-β40 (Aβ40), Aβ42 and phosphorylated tau-181 (pTau181) were measured in blood from 142 people with iRBD. Among people who went on to develop DLB, the ratio of Aβ40 to Aβ42 was lower and the levels of pTau181 were higher than among people who did not develop DLB.