C9orf72 and frontotemporal dementia: Some more studies have shown that there is a large hexanucleotide (GGGGCC) repeat expansion in the first intron of C9ORF72 on the affected haplotype [22], and a common Mendelian genetic lesion in C9orf72 is implicated in many cases of sporadic and familial ALS and FTD [23].