A metabolic disorder caused by genetic defects is representedbyPrader–Willi syndrome (PWS), which is characterized by severalsymptoms, including obesity, hyperphagia, low GH, neonatal hypoglycemia,infertility, and accelerated mortality.156,157 Though many studies suggest that high ghrelin levels might be responsiblefor hyperphagia and obesity in patients with PWS,158 this association has never been demonstrated. This evidence concerns the gene GHRL and obesity due to melanocortin 4 receptor deficiency.