As the lysosomal defects observed in C9-KO MNs are less severe than those observed in C9orf72 patient MNs, our data suggests that while C9orf72 haploinsufficiency impacts lysosomal health, it is unlikely to be the primary factor contributing to neuronal lysosomal dysfunctions in C9orf72 ALS/FTD. This evidence concerns the gene C9 and frontotemporal dementia.