Several studies have revealed a reduction in skeletal mitochondrial mass in obesity and type 2 diabetes (Kelley et al., 2002; Morino et al., 2005; Ritov et al., 2005), decreased ATP synthesis in insulin resistant offspring of patients with type 2 diabetes (Petersen et al., 2004, 2005) and decreased maximal respiration rates in skeletal muscle isolated mitochondria from type 2 diabetics (Mogensen et al., 2007). The gene discussed is INS; the disease is obesity due to melanocortin 4 receptor deficiency.