MSTN and obesity due to melanocortin 4 receptor deficiency: It is not known which, if any, of these pathways may mediate the increase in circulating myostatin in obese patients, but it is tempting to speculate that elevated glucocorticoids commonly observed in metabolic syndrome and obesity (Anagnostis et al., 2009) could stimulate myostatin expression by promoter regulation (Allen et al., 2010) and modulation of miR-27a/b (Allen and Loh, 2011).