C9orf72 and frontotemporal dementia: The most common genetic causes of familial ALS involve autosomal-dominant mutations in the following four genes: C9ORF72 (uncharacterized) in 40–50% cases [89,90], also most commonly mutated in frontotemporal dementia (FTD), SOD1[141] in 20% [142], TARDBP (encoding the TDP-43 protein) [143] and FUS (fused in sarcoma) [144,145] in 4% [146] of fALS cases, respectively.