1. Northern Institute for Cancer Research, Newcastle University, Newcastle upon Tyne NE2 4AD, U.K.
2. Cancer Biology Group, University of Dundee, Division of Pathology and Neuroscience, Ninewells Hospital and Medical School, Dundee DD1 9SY, U.K.
3. Institute for Human Genetics, Newcastle University, Newcastle upon Tyne NE2 4AD, U.K.