School for Mental Health and Neuroscience, Maastricht University, Maastricht, Netherlands. Department of Human Genetics, Radboud University Medical Center, Nijmegen, Netherlands. Department of Clinical Chemistry, Canisius-Wilhelmina Hospital, Nijmegen, Netherlands. Department of Neurology, Zuyderland Medical Center, Sittard-Geleen, Netherlands. Central Diagnostic Laboratory, Maastricht University Medical Center, Maastricht, Netherlands. MS Center ErasMS, Departments of Neurology and Immunology, Erasmus University Medical Center, Rotterdam, Netherlands. Department of Neuroimmunology, Netherlands Institute for Neuroscience, Amsterdam, Netherlands.