The Journal of clinical investigation
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Over 20 severely obese subjects in 11 independent kindreds have been reported to have pathogenic heterozygous mutations in the gene encoding the melanocortin 4 receptor (MC4R), making this the most common known monogenic cause of human obesity. To date, the detailed clinical phenotype of this dominantly inherited disorder has not been defined, and no homozygous subjects have been described. We determined the nucleotide sequence of the entire coding region of the MC4R gene in 243 subjects with severe, early-onset obesity. ⋯ In addition, a marked increase in bone mineral density was seen in all affected subjects. In transient transfection assays, the N62S mutant receptor showed a responsiveness to alphaMSH that was intermediate between the wild-type receptor and mutant receptors carrying nonsense and missense mutations associated with dominantly inherited obesity. Thus MC4R mutations result in a syndrome of hyperphagic obesity in humans that can present with either dominant or recessive patterns of inheritance.