C9orf72 and frontotemporal dementia: Across sporadic and genetic FTD, CSF NfL levels are higher compared to patients with Alzheimer’s disease or controls.7,8,40 Serum NfL levels follow a similar pattern to CSF, with FTD-GRN reported as higher on average (61.5 pg/ml) compared with FTD-C9orf72 (33.9 pg/ml).