C9orf72 and amyotrophic lateral sclerosis: Consistently, decreased neuronal cell viability can be caused by conditioned medium from cultured mouse and human astrocytes lacking TDP-43 expression [54], expressing mutant forms of TDP-43 [55], FUS [56], and C9orf72 [57], or even overexpressing wild-type FUS [58], which is known to cause ALS pathology in patients [59,60], and wild-type TDP-43 [48].