TARDBP and frontotemporal dementia: The discovery of the GGGGCC hexanucleotide expansion on chromosome 9 (C9orf72)5, 6 in families with cases of ALS, FTD, and ALS-FTD established a genetic link between the two conditions and supports previous observations of common neuropathological abnormalities in ALS and FTD (i.e., the accumulation of the DNA/RNA binding protein TDP-43)7.