APOE and Parkinson disease: The top 20 Parkinson’s disease genes according to the degree of Betweenness centrality are SNCA, AKT1, TP53, INS, TNF, ALB, MT-CYB, IL-6, PRKN, APOE, SQSTM1, HTT, GBA, CD4, MMP9, APP, TLR2, RPS27A, PPARG and GALC.