GHRL and Parkinson disease: Measurements of the fasting and postprandial serum levels of the orexigenic peptide ghrelin (implicated in promoting gastrointestinal motility and influencing higher brain functions) in 20 healthy controls, 39 (including 19 drug-naïve) PD patients and 11 iRBD patients have shown a less pronounced recuperation of the decrease of this peptide in the early postprandial phase in iRBD and PD patients than in controls, suggesting that ghrelin excretion should be a peripheral biomarker of both diseases [125].