However, reduction of Mfn2 expression together with decreased mitochondrial size in skeletal muscle in obesity and type 2 diabetes states allow proposing a relevant role for Mfn2 in IR (Civitarese and Ravussin, 2008; Zorzano et al., 2009a,b). Here, MFN2 is linked to obesity due to melanocortin 4 receptor deficiency.