1 Wellcome Trust Sanger Institute, Wellcome Genome Campus, Hinxton, Cambridge CB10 1SD, UK; and at the Department of Paediatrics, University of Cambridge, Cambridge, Hills Road, CB2 0QQ, UK.
2 Institute of Cellular Medicine, Newcastle University, Framlington Place, Newcastle upon Tyne NE2 4HH, UK; and at the Department of Dermatology and Newcastle Biomedical Research Centre, Newcastle Hospitals NHS Foundation Trust, Queen Victoria Road, Newcastle upon Tyne NE2 4LP, UK.