1. MRC Molecular Haematology Unit, Weatherall Institute of Molecular Medicine, Oxford University, Oxford OX3 9DS, UK
2. European Bioinformatics Institute, Wellcome Trust Genome Campus, Hinxton, Cambridge CB10 1SD, UK
3. Computational Biology Research Group, Weatherall Institute of Molecular Medicine, Oxford University, Oxford OX3 9DS, UK
4. Wellcome Trust Centre for Human Genetics, Oxford OX3 7BN, UK