C9orf72 and frontotemporal dementia: More recently, in familial amyotrophic lateral sclerosis (ALS) and frontotemporal dementia (FTD), a hexanucleotide block (CCGGGG)n in the C9orf72 locus which is normally a few tens of repeats in size has been shown to expand to thousands of base pairs (DeJesus-Hernandez et al., 2011; Renton et al., 2011).