Mutations in several genes appear to be specific for either FTD or ALS (e.g., superoxide dismutase 1 [SOD1]); however, most have been detected in both diseases, like the repeat expansion in C9orf72. Furthermore, TAR DNA-binding protein 43 (TDP-43) inclusions can be observed in approximately 50% of FTD patients and more than 90% of ALS patients [43, 44]. Here, C9orf72 is linked to frontotemporal dementia.