1. Department of Rheumatology and Clinical Immunology, University Medical Center Groningen, University of Groningen, The Netherlands.
2. Department of Internal Medicine, Division of Nephrology, University Medical Center Groningen, University of Groningen, The Netherlands.
3. Department of Rheumatology and Clinical Immunology, University Medical Center Groningen, University of Groningen, The Netherlands. k.de.leeuw@umcg.nl