1. Department of Medicine, University College London Medical School, London
2. St Bartholomews Hospital, London
3. Universitäts Kinderklinik, Göttingen, Germany
4. Royal Sussex County Hospital, Brighton
5. Colorado Sickle Cell Treatment and Research Center, University of Colorado School of Medicine, Denver, Colorado, U.S.A.
6. Department of Medicine, Highland Hospital, Rochester, New York, U.S.A.
7. Department of Pediatrics, University of California, San Francisco, California, U.S.A.