A study of 90,000 people has uncovered new genetic variants that influence fat mass, weight and risk of obesity. The variants act in addition to the recently described variants of the FTO gene: adults carrying variants in both genes are, on average, 3.8 kg (or 8.5 lb) heavier. The variants map close to a gene called MC4R: mutations in this gene are the most common genetic cause of severe familial obesity.