GCG and obesity due to melanocortin 4 receptor deficiency: Thus, GLP-1 receptor agonists and inhibitors of GLP-1 hydrolysis are now front-line therapies for type 2 diabetes (T2D) (Campbell and Drucker, 2013; Nauck, 2011), and PYY and OXM analogues, which regulate appetite and control energy expenditure, are both currently being developed to treat obesity.