We are working on this study with St Georges Hospital Medical School. The hormone leptin normally matches appetite to the body’s energy needs, but levels are higher than normal in overweight people, in whom it doesn’t seem to work properly. Leptin also causes changes in blood vessels leading to atherosclerosis and high levels could be one of the reasons for the well-known link between obesity and heart disease. Leptin may be ineffective in controlling appetite because of over-activity of an enzyme, protein tyrosine phosphate. This study will look for variations in the gene linked to overweight in around 2800 women and attempt to confirm any findings in a second smaller group.