The plasmatic levels of the measured metabolites (TYRA, β-PEA, OCT, TRY, SYN, NE, 5-HT, E, MTN, ADE, GABA, TYRO, TRP) were compared among DN, PD and H groups by Kruskal-Wallis test followed by Dunn’s multiple comparisons test. The gene discussed is PLXNA2; the disease is Parkinson disease.