The most frequent known causes of amyotrophic lateral sclerosis (ALS) and frontotemporal dementia (FTD) are mutations in the C9orf72 gene, which account for 40% of familial and 5% of sporadic ALS cases, and act as a main genetic cause of FTD (DeJesus-Hernandez et al., 2011; Renton et al., 2011; Majounie et al., 2012; Suh et al., 2015; Van Mossevelde et al., 2017). Here, C9orf72 is linked to frontotemporal dementia.