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

Objective: To search for mutations in melanocortin pathway elements, that i s, the melanocortin-4 receptor (MC4R), agouti-related protein (AGRP), and ( alpha -melanocyte-stimulating hormone (alpha MSH) genes in children with se vere obesity. Study design: Direct sequencing of the MC4R encoding sequence and single-st rand polymorphism conformation analysis of AGRP and all alpha MSH genes wer e 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 subjec ts. Results: Four dominantly inherited, heterozygous, missense MC4R mutations ( Val50Met, Ser58Cys, Ile102Ser, and Ile170Val) were identified in 4 unrelate d children and none of the control subjects. Expression of the obese phenot ype was variable in mutation-positive family members. Clinical and laborato ry features were similar in the obese children with and without an MC4R mut ation. Two polymorphisms were detected in the AGRP-encoding sequence (a sil ent mutation in exon 1 and Ala67Thr in exon 2), with similar frequencies in the obese and control groups. No mutations were found in the alpha MSH gen e. Conclusions: MC4R mutations may be a non-negligible cause of severe obesity in children with variable expression and penetrance. Mutations in AGRP and alpha MSH genes were not among the causes of obesity in our population.