Notwithstanding this, also regarding blood NFL, several investigations reported higher serum or plasma levels in patients with GRN mutations as compared with patients without mutations in known genes, patients with MAPT mutations, or patients with the C9orf72 HRE (including patients with ALS-FTD) (Meeter et al., 2016; van der Ende et al., 2019; Benussi et al., 2020; Heller et al., 2020b; Rojas et al., 2021). Here, C9orf72 is linked to amyotrophic lateral sclerosis.