Homozygous loss of MC4R function, and homozygous loss of proopiomelanocortin gene function, a preprohormone precursor of the endogenous MC4R agonist have both been reported in patients with early onset obesity (Farooqi et al., 2003; Krude et al., 1998). The gene discussed is POMC; the disease is obesity due to melanocortin 4 receptor deficiency.