C9orf72 and frontotemporal dementia: In 2011, an additional major genetic determinant was found in families with FTD and Amyotrophic lateral sclerosis (ALS): an intronic expansion of a hexanucleotide repeat in the C9orf72 gene, located on chromosome 9, where previous linkage studies had had identified an FTD/ALS locus (DeJesus-Hernandez et al., 2011; Renton et al., 2011).