1. Department of Neurology; University of Maryland School of Medicine; Baltimore Maryland USA
2. Department of Physical Therapy & Athletic Training; Boston University; Boston Massachusetts USA
3. Department of Epidemiology and Public Health; University of Maryland School of Medicine; Baltimore Maryland USA
4. Department of Neurology; Oregon Health and Science University and Portland VA Medical System; Portland Oregon USA
5. Department of Rehabilitation Science; KU Leuven-University of Leuven; Heverlee Belgium
6. Struthers Parkinson's Center; Golden Valley Minnesota USA
7. Department of Neurology; Radboud University Medical Center; Nijmegen The Netherlands
8. Department of Physical Therapy & Rehabilitation; University of Maryland School of Medicine; Baltimore Maryland USA
9. Avid Radiopharmaceuticals; Philadelphia PA USA
10. Department of Neurology; Rush University Medical Center; Chicago USA
11. UCL Institute of Neurology; University College London; UK
12. National Center of Epidemiology and CIBERNED; Carlos III Institute of Health; Madrid Spain