Many studies aiming to elucidate the potential causes of hyperphagia in PWS have identified factors that might contribute to the absence of satiety in PWS, including high levels of the orexigenic hormone ghrelin persisting in the postprandial state, low levels of pancreatic polypeptide, and a lack of the postprandial polypeptide YY peak [5–11]. Here, PPY is linked to Prader-Willi syndrome.