C9orf72 and amyotrophic lateral sclerosis: In accordance with this hypothesis, oligodendrocytes derived from ALS patients carrying disease-related mutations in SOD1, TARDBP, C9orf72, or FIG4 phosphoinositide 5-phosphatase induced in vitro neuronal hyperexcitability and subsequent motor neuron cell death (Ferraiuolo et al., 2016).