Inactivation of the Fto gene protects from obesity

Variations in the human FTO gene have been linked to obesity-related traits in several genome-wide association studies. A functional correlation is now reported between Fto, the equivalent gene in the mouse, and obesity. In Fto-deficient mice there is postnatal growth retardation and a lean phenotype with high energy expenditure and reduced fat accumulation. This suggests that Fto/FTO is involved in homeostasis via the control of energy expenditure. This study shows that mice lacking the Fto gene do not grow properly after birth, and have less adipose tissue and lean body mass. This is due to increased energy expenditure and systemic sympathetic activation, even though these mice move less and eat lots. Several independent, genome-wide association studies have identified a strong correlation between body mass index and polymorphisms in the human FTO gene1,2,3,4. Common variants in the first intron define a risk allele predisposing to obesity, with homozygotes for the risk allele weighing approximately 3 kilograms more than homozygotes for the low risk allele1. Nevertheless, the functional role of FTO in energy homeostasis remains elusive. Here we show that the loss of Fto in mice leads to postnatal growth retardation and a significant reduction in adipose tissue and lean body mass. The leanness of Fto-deficient mice develops as a consequence of increased energy expenditure and systemic sympathetic activation, despite decreased spontaneous locomotor activity and relative hyperphagia. Taken together, these experiments provide, to our knowledge, the first direct demonstration that Fto is functionally involved in energy homeostasis by the control of energy expenditure.