CLSTN3 and obesity due to melanocortin 4 receptor deficiency: Clstn3b consists of three exons, with the first exon residing in an intron of Clstn3 and the last two exons shared with Clstn3. Interestingly, Clstn3b regulates energy homeostasis by controlling sympathetic innervation of BAT and thermogenesis in a direction opposite to that of Clstn3; Clstn3b knockout mice are obese and have increased blood glucose levels compared with wild-type littermates, whereas mice overexpressing Clstn3b in BAT are lean and resistant to diet-induced obesity.