C9orf72 and frontotemporal dementia: Similarly, ALS and FTD share the pathological feature of aggregated proteins such as dipeptide repeats (DPRs) that are transcribed from the hexanucleotide repeat expansion within intron 1 of chromosome 9 open reading frame 72 (C9ORF72) [5, 6], TAR-DNA binding protein (TDP-43) [7, 8] and fused in sarcoma (FUS) [9–11].