MC4R and obesity due to leptin receptor gene deficiency: The majority of the children with LEP or LEPR deficiency displayed excessive weight gain and hyperphagia that were noticed at a far earlier age in postnatal life (before 1 year of age; mean ages in children with LEP deficiency: 0.3 ± 0.04 years [n = 83] and in children with LEPR deficiency: 0.9 ± 0.1 years [n = 27]) as compared with those in children with MC4R deficiency (mean age: 4 ± 3.3 years [n = 20]).