1. University Medical Center Utrecht, Utrecht University; Utrecht The Netherlands
2. Leiden University Medical Center; Leiden The Netherlands
3. Sophia Children's Hospital, Erasmus University Medical Center; Rotterdam The Netherlands
4. St. Franziskus-Hospital, Muenster, Germany, and University of Duisburg; Essen Germany
5. University of Muenster; Muenster Germany
6. German Rheumatism Research Center Berlin-Leibniz Institute and Charite University Medicine; Berlin Germany
7. University Medical Center Utrecht, Utrecht, The Netherlands, and University of California; Los Angeles
8. Radboud University Medical Center; Nijmegen The Netherlands
9. Emma Children's Hospital AMC and Amsterdam Rheumatology and Immunology Center Reade; Amsterdam The Netherlands
10. University of Leuven and University Hospitals Leuven; Leuven Belgium
11. University Children's Hospital; Zurich Switzerland
12. Emma Children's Hospital AMC and University of Amsterdam; Amsterdam The Netherlands
13. University Medical Center Utrecht, Utrecht, The Netherlands, and Oxford University; Oxford UK