We are involved in this study in conjunction with St Georges Hospital Medical School. The study started in mid-2002 and it is due to end in mid 2005. The hormone leptin signals the amount of stored fat to the brain, which adjusts feeding and energy release to maintain constant reserves. Overweight individuals are resistant to leptin, leading to a build-up of fat, which can eventually lead to obesity and related disorders. A disturbance of the mechanism by which leptin signals its effect in the brain could account for its failure to control appetite. Low-cost rapid laboratory techniques and new statistical approaches will be used to detect small effects of any of the genes for the leptin-signalling pathway on measures of body weight, in a large population of adult female twin pairs. Knowledge of genetic markers for overweight susceptibility in this group will allow us to identify at-risk individuals in the general population for advice and treatment.