Many of the genes, such as AgRP (Agouti-related peptide), PYY (peptide tyrosine tyrosine, and orexigenic), or MC4R (melanocortin-4 receptor), were identified as causing monogenic obesity and deregulating appetite and body weight control systems, where hormonal signaling (ghrelin, leptin, and insulin) is sensed by receptors located in the hypothalamus (arcuate nucleus) [33]. This evidence concerns the gene MC4R and obesity due to melanocortin 4 receptor deficiency.