Besides lifestyle and environmental factors, such as eating behaviour and physical activity, genetic ML264 predispositions play a basic role in the development of obesity. In general, control of energy homeostasis is based on the regulation of food Testosterone undecanoate intake. This regulation mainly takes place in the hypothalamus. Especially two populations of neurons expressing NPY/AgRP and POMC/CART in the arcuate nucleus play an important role in the regulation of food intake. One of the appetite regulating proteins is leptin, a circulating hormone, released by adipocytes. It acts via binding to leptin receptors in the hypothalamus and thus inhibiting appetite stimulating neuropeptides NPY and AgRP on the one hand and activating appetite suppressing transmitters POMC and CART on the other hand. Consequently, leptin deficiency leads to hyperphagia, resulting in severe obesity and hyperinsulinemia in human. Genome-wide association studies of obese people indicated about 50 genes to be involved in body weight regulation. One of these genes is the Fat mass and obesity associated gene FTO. In several studies, SNPs in the FTO gene were highly associated with increased body mass index. These studies could show that individuals carrying a risk allele exhibit about 1.5 kg higher weight than those with non-risk alleles most likely due to an increase in food intake. Consequently, the relation of leptin to FTO was addressed in further studies. Whereas one study could show that leptin downregulates FTO another one provided evidence for a regulation of leptin signaling by FTO. Thus, loss of FTO should result in a loss of leptin signaling and therefore hyperphagia. Further characterization of FTO function by generating Fto2/2 mice revealed FTO as an elementary protein in regulating energy homeostasis. In previous studies, we and others showed that loss of Fto leads to postnatal growth retardation and reduction in weight. Excess of lipids in the blood leads to dysregulation of energy storage and ectopic fat accumulation within and around different organs. This increased accumulation can impair the function of these organs and thus interfere with the health status of individuals.