When compared to controls, individuals with PD exhibited significantly reduced concentrations of total ghrelin (SMD: −0.45, 95% CI −0.62, −0.29; Z = 5.42; P < 0.00001) and active ghrelin (SMD: −0.80, 95% CI −1.24, −0.35; Z = 3.51; P = 0.0004) postprandially. The gene discussed is GHRL; the disease is Parkinson disease.