NEFL and primary progressive aphasia: Pertaining to FTD clinical subtypes, no correlation between serum NFL and age was found in bvFTD by Steinacker et al. (2018), whereas the same group observed a weak correlation between serum NFL and age at onset in all forms of PPA together as well as in nfvPPA and svPPA considered individually, while the correlation was stronger for lvPPA, which, again, is not surprising considering that AD pathology most commonly underlies this clinical variant (Steinacker et al., 2017b).