INS and obesity due to melanocortin 4 receptor deficiency: In most studies, the Arg64/X variant coexisted with increased body mass (overweight or obesity), decreased insulin sensitivity and glucose control, and raised risk of metabolic syndrome and early onset of diabetes mellitus type 2 (Oeveren et al. 2001; Oizumi et al. 2001; Tamaki et al. 2006).