SOD1 and frontotemporal dementia: Given this common cause of sALS with FTD, 10% of sALS and an additional 10% of FTD, the next question, given that it has taken more than 25 years with SOD1 mutations, is just how cytotoxicity occurs with the GGGGCC (G4C2) HRE within the C9ORF72 gene?