Expansions of a GGGGCC repeat within the first intron of the C9orf72 gene are the most common genetic cause of both amyotrophic lateral sclerosis (ALS) and frontotemporal dementia (FTD), two rapidly progressive and incurable neurodegenerative disorders (Dejesus‐Hernandez et al, 2011; Renton et al, 2011). The gene discussed is C9orf72; the disease is frontotemporal dementia.