LEP and obesity due to melanocortin 4 receptor deficiency: Other studies used obesity-dependent models of type 2 DM that derived from a mutation of the gene encoding leptin (ZDF rats) or its receptor (db/db mice), whose normal function precludes obesity by regulating food intake, glucose homeostasis and energy expenditure (Marwarha and Ghribi, 2012; Forny-Germano et al., 2019).