Following identification of the GGGGCC repeat expansion in C9orf72 in ALS-FTD, screening of FTD cases found the repeat expansion accounted for 25.1 % of familial FTD and 5.8 % of sporadic cases worldwide, although, as with ALS, the frequency does vary within different populations [11]. Here, C9orf72 is linked to amyotrophic lateral sclerosis.