This isoform is involved in energy homeostasis and immunity.94 In the C57BL/KsJ- db/db mutant mouse model of type 2 diabetes, it is expressed in low levels resulting in these mice displaying an early obesity phenotype.95 The shorter isoforms (Lep-Ra, Lep-Rc, and Lep-Rd) function to internalize and degrade Leptin. This evidence concerns the gene LEP and obesity due to melanocortin 4 receptor deficiency.