Investigations of melanocortin-receptor genes in patients with severe childhood obesity

Melanocortin signalling plays a fundamental role in hypothalamic control of energy homeostasis. We investigated 62 patients with obesity (BMI>99.5 perc: 45 patients; BMI>97. -99.5 perc:17 patients) participating in our outpatient training program for obese children. The investigated families showed 6 affected sib-pairs (patient, affected sibling and parents) and 28 trios (patient, affected parents). After DNA isolation melanocortin receptor MC3R- and MC4R-genes were investigated by PCR and subsequent single strand conformation polymorphism (SSCP) analysis which was followed in suspicious cases by gene sequencing. In 11 patients SSCP for MC3R PCR-fragments was different from wildtype pattern. By sequencing we detected Ile81Val in 8 patients and Lys6Thr in 3 patients. MC4R SSCP was different to wildtype in 5 patients. Here we found the Ile169Ser polymorphism in 4 patients and a heterozygous Tyr302Phe mutation in one girl. This mutation, which has not yet been described, affects the seventh transmembrane domain of the receptor and is associated with severe obesity in the 12 year-old girl (BMI 34kg/m², >99.5 perc.; height 75. perc.) and hyperinsulinemia (insulin basal 45 mU/ml, after oral glucose load max. 300 mU/ml). Both her parents are obese (BMI father: 30.2, mother 31.9kg/m²), but only the father carries the same mutation which matches to a autosomal-dominant inherited heterozygous loss-of-function. In conclusion a new MC4R-gene mutation has been found in a family with severe obesity. SSCP is an unexpensive screening method to detect DNA nucleotide changes due to polymorphisms or missense mutations. Beside MC4R mutations, which are known to frequently lead to severe obesity, MC3R mutations may also be associated with obesity.

The study has been supported by Bonfor Research Foundation