We have employed a cellular model to differentiate possible mechanisms of toxicity exerted by expansion of the G4C2 hexanucleotide tract within the C9orf72 locus, the most frequent genetic cause of ALS and FTD (DeJesus-Hernandez et al., 2011; Renton et al., 2011). The gene discussed is C9orf72; the disease is amyotrophic lateral sclerosis.