1 Human Genetics, Wellcome Trust Sanger Institute, Cambridge CB10 1SA, UK. Electronic address: am33@sanger.ac.uk.
2 Addictions Department, Institute of Psychiatry, King's College London, London, UK; Centre for Molecular, Environmental, Genetic and Analytic Epidemiology, Melbourne School of Population and Global Health, University of Melbourne, Melbourne, Australia.
3 Human Genetics, Wellcome Trust Sanger Institute, Cambridge CB10 1SA, UK.
4 Department of Clinical Genetics, Addenbrooke's Hospital, Cambridge, UK.
5 The Ethox Centre, Nuffield Department of Population Health, University of Oxford, Oxford, UK.