C9orf72 and amyotrophic lateral sclerosis: C9orf72 ALS/FTD postmortem brain tissues exhibit extensive microglial pathology in the corticospinal tract and corpus callosum compared to non-C9orf72 ALS patients and control cases (Brettschneider et al., 2012; Cooper-Knock et al., 2012; Cardenas et al., 2017).