A Novel Loss Of Function Melanocortin-4-Receptor Mutation (Mc4r-F313sfs*29) In Morbid Obesity

Context: Melanocortin receptor-4 (MC4R) gene mutations are associated with earlyonset severe obesity, and the identification of potential pathological variants is crucial for the clinical management of patients with obesity.Objective: To explore whether and how a novel heterozygous MC4R variant (MC4RF313Sfs*29), identified in a young boy (body mass index [BMI] 38.8 kg/m(2)) during a mutation analysis conducted in a cohort of patients with obesity, plays a determinant pathophysiological role in the obesity development.Design Setting and Patients: The genetic screening was carried out in a total of 209 unrelated patients with obesity (BMI >= 35 kg/m(2)). Structural and functional characterization of the F313Sfs*29-mutated MC4R was performed using computational approaches and in vitro, using HEK293 cells transfected with genetically encoded biosensors for cAMP and Ca2+.Results: The F313Sfs*29 was the only variant identified. In vitro experiments showed that HEK293 cells transfected with the mutated form of MC4R did not increase intracellular cAMP or Ca2+ levels after stimulation with a specific agonist in comparison with HEK293 cells transfected with the wild type form of MC4R (Delta R/R0 =-90% +/- 8%; P < 0.001). In silico modeling showed that the F313Sfs*29 mutation causes a major reorganization in the cytosolic domain of MC4R, thus reducing the affinity of the putative Galpha S binding site.Conclusions: The newly discovered F313Sfs*29 variant of MC4R may be involved in the impairment of a-MSH-induced cAMP and Ca2+ signaling, blunting intracellular G protein-mediated signal transduction. This alteration might have led to the dysregulation of satiety signaling, resulting in hyperphagia and early onset of obesity.