1. Faculty of Medicine, University of Iceland , Reykjavik, Iceland
2. Perelman School of Medicine, University of Pennsylvania , Philadelphia, PA, USA
3. Centre of Public Health Sciences, University of Iceland , Reykjavik, Iceland
4. Centre for Rheumatology Research, Landspitali University Hospital , Reykjavik, Iceland
5. Department of Hematology, Landspitali University Hospital , Reykjavik, Iceland
6. Department of Epidemiology and Biostatistics, Center for Clinical Epidemiology and Biostatistics, University of Pennsylvania Perelman School of Medicine , Philadelphia, PA, USA
7. Division of Rheumatology, University of Pennsylvania Perelman School of Medicine , Philadelphia, PA, USA
8. Department of Science and Research, Landspitali University Hospital , Reykjavik, Iceland