Using an average penetrance of 60% for heterozygous carriers and 100% for homozygous and compound heterozygous carriers, as previously reported in literature [41], partial MC4R deficiency may explain obesity in 256,021 individuals, whereas complete MC4R deficiency may be the cause of obesity for only 149 subjects in the US population. The gene discussed is MC4R; the disease is obesity due to melanocortin 4 receptor deficiency.