C9orf72 and frontotemporal dementia: However, the frequency of C9orf72-related ALS-FTD (and C9orf72-ALS and C9orf72-FTD) patients positive for the presence of repeat expansion in C9orf72 varies between different populations and ethnicities; whilst the C9orf72 G4C2 HRE is the most frequent cause of ALS-FTD, ALS and FTD in European and North American populations, it was found to be extremely rare in Asia and the Middle East (Majounie et al., 2012).