A study by Farooqi et al. (2003) supported haploinsufficiency of MC4-R by demonstrating that individuals with heterozygous MC4R mutations express a less severe phenotype of hyperphagia, obesity, increased lean mass, increased linear growth, and hyperinsulinemia than individuals with homozygous MC4R mutations [12]. Here, MC4R is linked to obesity due to melanocortin 4 receptor deficiency.