C9orf72 and frontotemporal dementia: Thus, for this part of our study, we compared Aβ42, τT, τp-181 and TDP-43 CSF levels and the τP-181/τT ratio in FTD and/or ALS patients carrying the hexanucleotide C9orf72 repeat expansion, rare intronic C9orf72 variants or the p.Asn207Ser (p.N207S) exonic C9orf72 variant to patients without these variants.