1. Leukaemia Research Fund Molecular Haematology Unit, Department of Haematology, and Institute of Molecular Medicine, John Radcliffe Hospital, Oxford, U.K., LRF Preleukaemia Unit, Department of Haematology, University of Wales College of Medicine, Cardiff, U.K., Department of Haematology, University College Hospital, London, U.K., and Division of Haematology, Department of Medicine I, University of Vienna, Austria