C9orf72 and frontotemporal dementia: Mutations in the gene encoding transactive response DNA-binding protein 43 (TDP-43) cause some cases of FTD,10 and cytoplasmic inclusions containing phosphorylated and ubiquitinated forms of TDP-43 are prominent in FTD.10 Recently, it was found that hexanucleotide repeat expansions in C9ORF72 (a non-coding region on chromosome 9) are responsible for many cases of inherited and sporadic FTD and amyotrophic lateral sclerosis.11 TDP-43 pathology is a prominent feature in patients with C9ORF72 hexanucleotide repeat expansions.