Ghrelin/PYY might be a marker for orexigenic drive, as studies in subjects with Prader–Willi syndrome reported that subjects with hyperphagia due to PWS have hyperghrelinemia and attenuated PYY response to fat resulting in a high ghrelin/PYY ratio of 10 [5, 6]. This evidence concerns the gene PYY and Prader-Willi syndrome.