PRAP1 and obesity due to melanocortin 4 receptor deficiency: Proteomic profiling of 400+ patients identified 39 proteins associated with obesity and weight loss, including not only proteins previously studied in the context of obesity (in particular, adiponectin, C-reactive protein, and calprotectin), but also new putative biomarkers for weight loss/maintenance (e.g., D109 antigen and PRAP1).