INS and obesity due to melanocortin 4 receptor deficiency: The reason(s) underlying why conditions such as obesity exhibit an increase in muscle myostatin expression versus the relationship observed here are unknown, but may pertain to the role of myostatin in insulin sensitivity previously reported (Hittel et al., 2009) and supported by some, but not all of our correlative analysis of myostatin expression (such as in GSE18732; Figure 2i; Table 2).