1. Molecular Medicine and Haematology, School of Pathology, National Health Laboratory Service, University of the Witwatersrand, Johannesburg, South Africa;
2. Department of Haematology, Ampath Laboratories, Pretoria, South Africa;
3. Department of Molecular Pathology, Kings College Hospital, London, UK;
4. Department of Haematological Medicine, Kings College Hospital, London, UK;
5. Sickle Cell Branch, National Institutes of Health/National Heart Lung and Blood Institute, Bethesda, MD, USA