1. Public Health Genetics Unit, Strangeways Research Laboratory, Worts Causeway, Cambridge CB1 8RN
2. South Cambridgeshire Primary Care Trust, Fulbourn, Cambridge CB1 5EE
3. Division of Cardiovascular Medicine, Department of Medicine, University of Cambridge Addenbrooke's NHS Trust, Cambridge CB2 2QQ
4. Centre for Applied Statistics, Institute of Public Health, Cambridge CB2 2SR;
5. East Anglian Ambulance NHS Trust, Norwich NR6 5NA, UK