Importantly, Meijboom and colleagues57 have shown that injection of an AAV9 expressing Cas9 and gRNAs (deleting the repeats) led to reduction of RNA foci and dipeptide repeat proteins in transgenic ALS mouse models harboring 100–1,000 C9orf72 expanded repeats. The gene discussed is C9orf72; the disease is amyotrophic lateral sclerosis.