Prevalence, spectrum, and functional characterization of melanocortin-4 receptor gene mutations in a representative population-based sample and obese adults from Germany

Context: Autosomal dominant inheritance of mutations in the melanocortin-4 receptor gene (MC4R) is currently regarded as the most relevant genetic cause for extreme obesity and affects 2-4% of extremely obese individuals. Objective: Our objective was to assess the relevance of MC4R mutations in a German population-based sample. Design and Setting: We conducted a mutation screen of the MC4R gene by capillary electrophoresis-based single-strand conformation polymorphism analysis and denaturing HPLC. Participants: Subjects included 4068 individuals of a German population-based study group [Kooperative Gesundheitsforschung im Raum Augsburg, Survey 4 (KORA-S4); i.e. Cooperative Health Research in the Region of Augsburg] and 1003 German obese adults (body mass index ≥ 30 kg/m²). Main Outcome Measures: Samples with aberrant capillary electrophoresis-based single-strand conformation polymorphism analysis/denaturing HPLC patterns were resequenced. Functional studies including agonistic receptor stimulation (Nle-D-Phe-α-, α-, and β-MSH) and cell surface expression assays were performed. Results: Sixteen (six novel) coding nonsynonymous mutations were detected in 27 heterozygous individuals of KORA-S4. Four of the mutation alleles led to impaired receptor function in vitro; however, none of these six heterozygous mutation carriers was obese (body mass index ≥ 30 kg/m²). In the obese adults, six coding nonsynonymous and a nonsense mutation were detected in 13 individuals. Only the nonsense mutation allele entailed impaired receptor function. Conclusions: Our study depicts prevalence, spectrum, and functional characterization of MC4R mutations in the German population-based sample KORA-S4. In this epidemiological study group, individuals heterozygous for nonsynonymous MC4R mutation alleles entailing impaired function were not obese. Furthermore, nonsynonymous MC4R mutations causing impaired receptor function were rare in German obese adults (two in 1003 = 0.2%).