BioFINDER-Sleep study was established in 2021 and will include patients with early Parkinson´s disease (PD) and persons with iRBD to provide essential insights into the underlying mechanisms of the progressive neurodegenerative processes in central and peripheral nervous systems. Briefly polysomnography will be used to establish the presence of RBD in both the early PD cohort and in the iRBD cohort. Then, state of the art multimodal imaging techniques will be used, including, magnetic resonance imaging (MRI), positron emission tomography (PET) of the dopamine transporters (DAT-PET) to quantify dopamine terminal loss, and \[123I\] MIBG scintigraphy of the heart will be performed to quantify the loss noradrenaline terminals to the heart. In addition to this, synuclein seed amplification assays (SSAs) will be applied to cerebrospinal fluid (CSF) and skin samples to establish synuclein pathology status. Further, CSF and blood biomarkers will be developed that can be used to as prognostic markers. These investigations will be done in parallel to clinical assessments of motor and non-motor symptoms as well as assessment of cognitive function in a longitudinal setting.