Hexanucleotide repeat expansions (G4C2) in the 5’ non-coding sequence of the C9ORF72 gene was identified in 2011 as the most common inherited cause of ALS, FTD, and ALS-FTD (DeJesus-Hernandez et al., 2011; Renton et al., 2011). The gene discussed is C9orf72; the disease is frontotemporal dementia.