C9orf72 and amyotrophic lateral sclerosis: The potential of microglia to play a direct role in ALS pathogenesis was highlighted by the identification of several ALS linked genes that influence the function of, and are highly expressed in microglia, including C9ORF72, TBK1, and PGRN (Irwin et al., 2008; Freischmidt et al., 2015; Lall and Baloh, 2017).