Both the C9orf72 hexanucleotide repeat expansions and the transcribed RNA, were reported to adopt polymorphic unusual secondary structures, such as G-quadruplexes and hairpin, which were involved in the ALS/FTD pathogenesis via several potential mechanisms (Fratta et al., 2012; Reddy et al., 2013; Haeusler et al., 2014). Here, C9orf72 is linked to frontotemporal dementia.