142 cases of patients with iRBD will be recruited from the neurology department of Ruijin Hospital, th second Affiliated Hospital of Soochow University and wuhan Union Hospital. After the informed consent was signed, they were divided into a trial group and a control group randomly. Each group contains 71 cases. The patients in the trial group will be treated with Idebenone, while the patients in the control group was treated with placebo. Both groups of subjects will be treated for 5 years, and patients will be followed-up and evaluated in the first year, 3 years and 5 years after treatment. The observations include the MDS-UPDRS questionnaires evaluation, blood biomarker measurements and fMRI or PET-MR examination to make sure whether the patients has converted to synucleinopathies. Study hypothesis: Idebenone therapy for patients with iRBD is safe and effective in delaying disease progression into synucleinopathies.

Inclusion Criteria:

1. Clinical diagnosed of iRBD.
2. Age between 40 and 75.
3. Be voluntarily to participate in the experiment by signing an informed consent form.

Exclusion Criteria:

1. Sleep apnea hypopnea syndrome
2. Slow movement, muscle rigidity, tremor or postural instability.
3. Neurological diseases such as cerebral hemorrhage, cerebral infarction, brain trauma, brain tumor or central nervous system infection.
4. Other sleep disorders or seizures.
5. Alcoholism or drug addiction patients.