Therefore, the complexity of pathological RNA molecules of C9orf72 repeat expansion associated with ALS and FTLD demands further comprehensive studies as structures adopted by RNA transcripts act not only as important promoters of RNA toxicity-dependent mechanism but also present promising therapeutic targets in ALS, FTLD and other repeat-associated neurodegenerative diseases. The gene discussed is C9orf72; the disease is amyotrophic lateral sclerosis.