1. Department of Cell and Molecular Pathology, St John's Institute of Dermatology (GKT), St Thomas' Hospital, London SE1 7EH, U.K.,
2. Department of Dermatology and Cutaneous Biology, Jefferson Medical College, Philadelphia, PA, U.S.A.,
3. Department of Dermatology, Hospital for Sick Children, Great Ormond Street, London WC1N 3JH, U.K.,
4. Department of Dermatology, Royal Infirmary, Edinburgh EH3 9YW, U.K.