C9orf72 and frontotemporal dementia: A number of genes are linked to inherited forms of ALS/FTD but mutations in the C9orf72 gene represent by far the most common cause of familial ALS/FTD accounting for approximately 11% of ALS and 13% of FTD cases (Dejesus‐Hernandez et al., 2011; Renton et al., 2011).