SGIP1 and obesity due to melanocortin 4 receptor deficiency: Besides its originally identified function as a candidate gene for regulating energy balance and potentially important in determining obesity risk in humans [21, 22], several studies have also found that SGIP1 is an endocytic protein that functions as the molecular interface between the basic machinery of endocytosis and components of actin cytoskeletal rearrangements [23, 24].