Specifically, researchers identified individuals with congenital leptin deficiency [54], mutations in the gene encoding the LEPR [55], and mutations in multiple genes encoding components of the melanocortin pathway, including PCSK1 [56], MC4R [57], and POMC [58]; all these genetic alterations led to early-onset severe obesity. This evidence concerns the gene PCSK1 and obesity due to melanocortin 4 receptor deficiency.