[From gene to disease; leptin and obesity]

Homozygous mutations of the ob gene, encoding leptin, are associated with severe obesity, hyperphagia and insulin resistance in humans. Leptin conveys a signal from adipose tissue to hypothalamic nuclei that integrate whole body fuel metabolism, informing those nuclei about the magnitude of fuel reserves. In the absence of leptin, the brain perceives energy availability as insufficient and therefore activates powerful mechanisms to restore fuel depots. If leptin synthesis or signal transduction is perturbed in the presence of food, a severely obese phenotype ensues.