Abstract

Neurodegenerative diseases do not start suddenly. Parkinson’s disease (PD), in particular, has a 10–25-year prodromal period during which subtle symptoms and signs emerge but remain insufficient for a formal clinical diagnosis. Numerous markers of this early stage have been identified. One of the most powerful predictors is REM sleep behaviour disorder (RBD), a condition where individuals lose normal REM atonia and act out their dreams. Long-term studies show that roughly 80% of individuals with RBD eventually develop a synucleinopathy. This seminar will summarize the landscape of prodromal PD research, highlight the predictive value of RBD, explore opportunities offered by studying early-stage disease, and discuss how emerging biomarkers may reshape how we define these disorders.