CONTEXT: Congenital leptin deficiency is a very rare cause of severe early-onset obesity. We recently characterized a mutation in the leptin gene (p.D100Y), which was associated with detectable leptin levels and bioinactivity of the hormone. CASE DESCRIPTION: We now describe two siblings, a 9-year-old girl and a 6-year-old boy with severe early-onset obesity and hyperphagia, both homozygous for a c.309C>A substitution in the leptin gene leading to a p.N103K amino acid exchange in the protein and detectable circulating levels of leptin. In vitro experiments in a heterologous cell system demonstrated that the mutated protein was biologically inactive. Treatment with sc recombinant human leptin led to rapid improvement of eating behavior and weight loss. CONCLUSIONS: Sequencing of the leptin gene may need to be considered in hyperphagic, severely obese children with detectable levels of circulating leptin.This work was supported by Grant BMBF 01GI1120A from the Federal Ministry of Education and Research. Support was also provided by the Wellcome Trust (082390/Z/07/Z), the Medical Research Council, the National Institute for Health Research Cambridge Biomedical Research Centre, the European Research Council, and the Bernard Wolfe Health Neuroscience Fund (all to I.S.F.). J.-B.F. was supported by the International Graduate School in Molecular Medicine Ulm.This is the final version of the article. It first appeared from the Endocrine Society via http://dx.doi.org/10.1210/jc.2015-226
