GDF15 and obesity due to melanocortin 4 receptor deficiency: As a member of the transforming growth factor (TGF)-β subfamily, growth differentiation factor 15 (GDF-15) is a stress-responsive cytokine associated with various diseases such as cancers [1,2,3,4,5], cardiovascular disorders [6], mitochondrial disorders [7], hyperthyroidism [8], obesity and type 2 diabetes [9].