Loss of function of C9orf72 also disrupts autophagy and lysosomal function in multiple cell types (Farg et al., 2014; Ji et al., 2017; O'Rourke et al., 2015; Sellier et al., 2016; Shi et al., 2018; Sullivan et al., 2016; Ugolino et al., 2016; Webster et al., 2016; Yang et al., 2016; Zhu et al., 2020), suggesting a mechanism whereby G4C2 repeats may have synergistically detrimental effects with haploinsufficient C9orf72 in C9-ALS/FTD patients. Here, C9orf72 is linked to frontotemporal dementia.