A rare genetic disease with characteristics of early-onset severe obesity due to mutations in single genes acting on the development and function of the hypothalamus or the leptin-melanocortin pathway, leading to disruption of energy homeostasis and endocrine dysfunction. Patients present with a body mass index over three standard deviations above normal at less than five years of age, accompanied by a variety of signs and symptoms according to the mutated gene, including hyperphagia, insulin resistance, reduced basal metabolic rate or hypogonadism among others. [from SNOMEDCT_US]