Although leptin was originally considered an anti-obesity hormone because of its regulatory role in the maintenance of body weight (Friedman, 2016), there is growing evidence supporting the significant influence leptin exerts on both glycemic control (Lee et al., 2011; Morton and Schwartz, 2011) and cognitive function (Harvey, 2010; Yin et al., 2018; Forny-Germano et al., 2019) as well (Figure 1). This evidence concerns the gene LEP and obesity due to melanocortin 4 receptor deficiency.