Hormonal dysregulation, proinflammatory cytokines, myokines (including insulin-like growth factor 1 (IGF-1), myostatin, and irisin), and adipokines (including adiponectin and resistin) constitute crucial factors in muscle homeostasis and the pathogenesis of sarcopenic obesity. The gene discussed is IGF1; the disease is obesity due to melanocortin 4 receptor deficiency.