MSTN and obesity due to melanocortin 4 receptor deficiency: The transforming growth factor (TGF)-β superfamily is composed of 33 members including TGF-β1-3, activins, myostatin (also known as growth differentiation factor-8 [GDF8]), and bone morphogenetic proteins (BMPs); among them, TGF-β1, activin A, and myostatin (MST) are the components with an intimate relationship with obesity [8].