GHSR and obesity due to melanocortin 4 receptor deficiency: Although this potential mechanism requires further investigation, GHSR (Zigman et al. 2005, Fernandez et al. 2018), ghrelin (Wortley et al. 2005) and SDC3 (Reizes et al. 2001, Strader et al. 2004) knockout mice share the phenotypes of having impaired reflex hyperphagia after fasting and resistance to diet-induced obesity.