To test this hypothesis, we employed ALS fly models with motor neurons overexpressing arginine-rich dipeptide repeat proteins (DPRs: PR100 and GR100) derived from the GGGGCC repeat expansion in C9orf72, the most commonly mutated gene in ALS (DeJesus-Hernandez et al., 2011; Renton et al., 2011). The gene discussed is C9orf72; the disease is amyotrophic lateral sclerosis.