A hexanucleotide (GGGGCC) repeat expansion in the first intron of the C9orf72 gene was recently identified as a major contributing factor to the chromosome 9p21-linked diseases amyotrophic lateral sclerosis (ALS) and frontotemporal dementia (FTD) (Dejesus-Hernandez et al., 2011). Here, C9orf72 is linked to frontotemporal dementia.