Actin filament assembly and disassembly are necessary for axonal maintenance and synaptic strength (Flynn et al., 2012; Huang et al., 2013); thus, the alteration of this dynamic may account for the axonal phenotype observed in C9ORF72-depleted mouse motor neurons and iPSC-derived motor neurons from C9-ALS patients (Sivadasan et al., 2016). Here, C9 is linked to amyotrophic lateral sclerosis.