1. Dermatology Centre; University of Manchester; Manchester Academic Health Science Centre; Manchester U.K.
2. International Psoriasis Council; St Louis MO U.S.A.
3. School of Health Sciences; University of Manchester; Manchester Academic Health Science Centre; Manchester U.K.
4. Unit for Population-Based Dermatology Research; St John's Institute of Dermatology; Guy's and St Thomas’ NHS Foundation Trust and King's College London; London U.K.
5. Department of Dermatology; Bergamo General Hospital; and GISED Study Centre; Bergamo Italy
6. Department of Dermatology; Erasmus MC University Medical Centre; Rotterdam the Netherlands
7. Department of Dermatology; University Clinics of Hamburg; Hamburg Germany