GHRL and obesity due to melanocortin 4 receptor deficiency: Interestingly, it has been proposed that a decline in ghrelin system activity may play a role in age-dependent impairment of energy homeostasis and associated disease patterns like reduced appetite, obesity, diabetes or hepatic steatosis, but also cardiovascular dysfunction and neurodegenerative diseases (for review see Stoyanova, 2014; Yin and Zhang, 2016; Amitani et al., 2017).