GIPR and obesity due to melanocortin 4 receptor deficiency: GIPR is linked to obesity and several obesity-related traits, including body mass index and type 2 diabetes (Saxena et al. 2010; Speliotes et al. 2010; Fox et al. 2012; Okada et al. 2012; Wen et al. 2012, 2014; Berndt et al. 2013; Mahajan et al. 2014).