Defects in this gene have been associated with susceptibility to obesity (Ramos-Molina et al., 2016) and congenital proprotein convertase 1/3 deficiency (PC1/3 deficiency) (Martin et al., 2013; Pepin et al., 2019)—also called obesity with impaired prohormone processing [OMIM: 600955]. The gene discussed is PCSK1; the disease is obesity due to melanocortin 4 receptor deficiency.