C9orf72 and frontotemporal dementia: Recently, a hexanucleotide repeat expansion in chromosome 9 open reading frame 72 (C9ORF72), a gene of unknown function on chromosome 9p21, was reported as a major cause of disease in Finnish and North American FTD and ALS cohorts [4], [5], and has been observed in FTD and ALS cohorts worldwide [6].