This is in line with previous mass spectrometry-based reports identifying NfL peptides in insoluble protein inclusions and neurofibrillary tangles.29,30 The N-terminal domain of NfL is a region of low complexity and target of post-translational modifications including phosphorylation.31 Our assay included a peptide in the N-terminal domain of NfL [residues (31–37)], which was recovered from brain but largely reduced in CSF (Fig. 1B and C) and was more abundant in the control than in the tauopathy brains (Supplementary Fig. 1). This evidence concerns the gene NEFL and tauopathy.