C9orf72 and frontotemporal dementia: More widespread grey matter changes have been most prominent in studies of the 10–15% of patients with ALS with frank frontotemporal dementia (Chang et al., 2005), or in ALS genotypes such as C9orf72, which are more consistently associated with marked frontotemporal dementia-spectrum cognitive impairments (Bede et al., 2013a).