Author information: (1)Division of Psychiatry, University of Edinburgh, Edinburgh, EH10 5HF, UK. D.Howard@ed.ac.uk. (2)Division of Psychiatry, University of Edinburgh, Edinburgh, EH10 5HF, UK. (3)Centre for Cognitive Ageing and Cognitive Epidemiology, University of Edinburgh, Edinburgh, EH8 9JZ, UK. (4)Department of Psychology, University of Edinburgh, Edinburgh, EH8 9JZ, UK. (5)Social Genetic and Developmental Psychiatry Centre, Institute of Psychiatry, Psychology & Neuroscience, King's College London, London, SE5 8AF, UK. (6)NIHR Biomedical Research Centre for Mental Health, South London and Maudsley NHS Trust, London, SE5 8AF, UK. (7)Institute of Health and Wellbeing, University of Glasgow, Glasgow, G12 8RZ, UK. (8)Department of Medical Epidemiology and Biostatistics, Karolinska Institutet, Stockholm, 171 77, Sweden. (9)Department of Genetics, University of North Carolina, Chapel Hill, 27599 NC, USA. (10)Department of Psychiatry, University of North Carolina, Chapel Hill, 27599 NC, USA. (11)Medical Research Council Human Genetics Unit, Institute of Genetics and Molecular Medicine, University of Edinburgh, Edinburgh, EH4 2XU, UK.