C9orf72 and amyotrophic lateral sclerosis: Therefore, the concentrations of TDP-43 in plasma and CSF could be varied in ALS patients, especially in those harboring the mutation in TARDBP. A previous study described the CSF TDP-43 levels in ALS patients with hexanucleotide repeat expansion (HRE) in the C9orf72 gene, however, no difference in the CSF TDP-43 levels was observed between the C9orf72 expansion carriers and noncarriers in the cohort (11).