As well as ALS, C9orf72 GGGGCC repeat expansions are commonly found in FTD, and the spectrum of C9orf72 diseases extends from both ALS and FTD to other motor disorders such as primary lateral sclerosis (PLS), progressive muscular atrophy (PMA), and Huntington’s disease (HD) phenocopies, as well as other non-motor disorders, such as Alzheimer’s disease (AD). This evidence concerns the gene C9orf72 and frontotemporal dementia.