The microgliosis we observed previously in C9-ALS-FTSD24 is supported here by the upregulation of CD163, a marker of macrophage activity, and the downregulation of P2RY12, a marker of microglial homeostasis.50,51 The 20 significantly differentially expressed genes clustered into two similarly sized groups, those that were upregulated in C9-ALS-FTSD (SERPINA3, S100A10, FKBP5, EMP1, CD163, SPP1, CP, CTSE, BAG3) and those that were downregulated (ARC, RALB, EGR1, JUN, COX5B, P2RY12, BDNF, SLC17A6, BAD, MFGE8, FOS) relative to control cases. This evidence concerns the gene ARC and amyotrophic lateral sclerosis.