A Study of Efficacy and Safety of Idebenone Vs. Placebo in Prodromal Parkinson Disease

Inclusion Criteria: * Subjects are voluntary to participate and have signed informed consent * Diagnosed as Rapid Eye movement (REM) Sleep Behavior Disorder by polysomnography Exclusion Criteria: * Subjects are pregnant, breastfeeding, or want to get pregnant or breastfeeding in 2 years * Subjects have history of allergy to idebenone * Difficulty to communicate * Suffering from neurodegenerative diseases * Having obvious brain imaging abnormalities (eg. severe brain atrophy, malformation, softening lesions, cerebrovascular disease, intracranial occupancy, giant large benign lesions, etc.) * Having severe mental illness (eg. schizophrenia, manic depression, and severe depression) * Long-term use of clonidine, dopamine antagonists, and serotonin reuptake inhibitors * Suffering from other severe medical conditions * Having difficulty in moving and are unable to come to the hospital * Having claustrophobia * Having contraindications to MRI tests * Having history of olfactory disorders greater than 10 years * Having history of color vision disorders greater than 10 years * Life expectancy less than 2 years * Having other situations which researchers consider is inappropriate to participate in this study