MC4R and Bardet-Biedl syndrome: Examples of MO are melanocortin-4-receptor (MC4R), leptin-receptor (LEPR), and pro-opiomelanocortin (POMC) deficiency, while 16p11.2 deletion syndrome, Bardet-Biedl Syndrome (BBS) and deleterious mutations or methylation defects in GNAS (Guanine Nucleotide binding protein, Alpha Stimulating activity polypeptide) are often reported for SO.4