1. Department of Epidemiology Research, Statens Serum Institute, Copenhagen, Denmark
2. The Danish Multiple Sclerosis Registry, Rigshospitalet, Copenhagen, Denmark
3. Institute of Regional Health Research, University of Southern Denmark, Odense, Denmark
4. Multiple Sclerosis Clinic of Southern Jutland (Sønderborg, Vejle, Esbjerg), Department of Neurology, Sønderborg, Denmark
5. National Institute of Public Health, University of Southern Denmark, Copenhagen, Denmark