Mutational analysis of melanocortin-4 receptor, agouti-related protein, and α-melanocyte-stimulating hormone genes in severely obese children

Abstract

Objective: To search for mutations in melanocortin pathway elements, that is, the melanocortin-4 receptor (MC4R ), agouti-related protein (AGRP ), and (α-melanocyte-stimulating hormone (αMSH ) genes in children with severe obesity. Study design: Direct sequencing of the MC4R encoding sequence and single-strand polymorphism conformation analysis of AGRP and αMSH genes were performed in 63 severely obese children. Polymerase chain reaction (PCR) assays of restriction fragment length polymorphism were used to assess the frequency of each newly discovered mutation in 283 non-obese control subjects. Results: Four dominantly inherited, heterozygous, missense MC4R mutations (Val50Met, Ser58Cys, Ile102Ser, and Ile170Val) were identified in 4 unrelated children and none of the control subjects. Expression of the obese phenotype was variable in mutation-positive family members. Clinical and laboratory features were similar in the obese children with and without an MC4R mutation. Two polymorphisms were detected in the AGRP -encoding sequence (a silent mutation in exon 1 and Ala67Thr in exon 2), with similar frequencies in the obese and control groups. No mutations were found in the αMSH gene. Conclusions:MC4R mutations may be a non-negligible cause of severe obesity in children with variable expression and penetrance. Mutations in AGRP and αMSH genes were not among the causes of obesity in our population. (J Pediatr 2001;139:204-9)