C9orf72 and frontotemporal dementia: For example, the (GGGGCC)n hexanucleotide repeat expansion in intron 1 of C9orf72 is a major cause of ALS (amyotrophic lateral sclerosis) and FTD (frontotemporal dementia) and the (GGGGCC)n sequester hnRNP H RBP [7] and generates insoluble polypeptides specific to FTD/ALS [8].