Adipose insulin resistance is usually due to inflammation associated with obesity and the accumulation of excess lipids (Kern et al. 2001; Boden and Shulman 2002; Xu et al. 2003), but is typically not detected until it causes the loss of skeletal muscle insulin sensitivity (DeFronzo and Tripathy 2009). Here, INS is linked to obesity due to melanocortin 4 receptor deficiency.