PPP2CA and Parkinson disease: While PPP2CA, YWHAH, RAB11A and CDC42 which have been identified as hub genes/proteins in the M1 subnetwork network were also all central in the protein-protein interaction network (Fig 5B and S5 File) of genes differentially expressed upon HD and PD, only YWHAH was also central in the constructed co-expression network (Fig 5A and S5 File).