Dysregulation of the central leptin axis is considered a main cause of obesity (Ren 2004), but in humans it is primarily overeating that rapidly increases blood leptin levels, leading to leptin resistance and weight gain (Ren 2004; Berger and Kloting 2021; Schwartz et al. 1996). The gene discussed is LEP; the disease is obesity due to melanocortin 4 receptor deficiency.