The most frequent gene mutation among familial ALS/FTLD-TDP is hxanucleotide (intronic GGGGCC) expansion of C9orf72 [22,23]; approximately 40% of familial ALS patients have this mutation, and the mutation can manifest as any of the ALS, FTD-MND, and FTD phenotypes [13]. Here, C9orf72 is linked to frontotemporal dementia.