L F D van Vulpen1,2, S C Mastbergen3, R E G Schutgens4. 1. Van Creveldkliniek, University Medical Center Utrecht, Utrecht, the Netherlands. l.f.d.vanvulpen-2@umcutrecht.nl. 2. Department of Rheumatology & Clinical Immunology, University Medical Center Utrecht, Utrecht, the Netherlands. l.f.d.vanvulpen-2@umcutrecht.nl. 3. Department of Rheumatology & Clinical Immunology, University Medical Center Utrecht, Utrecht, the Netherlands. 4. Van Creveldkliniek, University Medical Center Utrecht, Utrecht, the Netherlands.