Received: 15 January 2020
Accepted: 11 May 2020
First Online: 16 May 2020
Ethics approval and consent to participate
: This study was conducted in accordance with the Declaration of Helsinki and the good clinical practices (GCP) guidelines after approval of the local ethics committees of the sites participating to the Parkinson’s Progression Markers Initiative (PPMI). PPMI is a multicentric longitudinal study involving United States, Greece, Spain, Austria, Germany, France, Italy, Norway, Israel, and Australia. Detailed information is available at ExternalRef removed. The relevant local institutional review boards approved the PPMI protocol and written informed consent was obtained from all participants prior to inclusion. No additional ethics approval was required from the local ethics committee where data was analysed.
: Not applicable.
: N.N. is part of the editorial board for BMC Neurology. P.R.B and V.G. declare that they have no conflict of interests.