ALS with frontotemporal dementia (ALS-FTD) is often caused by a polymorphic hexanucleotide repeat expansion (HRE) of GGGGCC (G4C2) in the first intron of the C9orf72 gene from normally less than 30 repeats into the hundreds or thousands, pathologically. This evidence concerns the gene C9orf72 and frontotemporal dementia.