1. King's College London, Department of Neurosciences Institute of Psychiatry, Psychology & Neuroscience and Parkinson Foundation Centre of Excellence, King's College Hospital Denmark Hill London UK
2. Department of Clinical and Movement Neurosciences UCL Queen Square Institute of Neurology London UK
3. Department of Psychiatry and Neurology Perelman School of Medicine at the University of Pennsylvania Philadelphia Pennsylvania USA
4. Parkinson's Disease Research Education and Clinical Center (PADRECC), Corporal Michael J. Crescenz Veterans Affairs Medical Center Philadelphia Pennsylvania USA
5. National Center of Epidemiology and CIBERNED, Carlos III Institute of Health Madrid Spain