Other studies report that NfL levels are elevated during active periods of multiple sclerosis and traumatic brain injury and normalise afterwards or after treatment.36 37 If this hypothesis on NfL release is correct, the change of NfL over time would associate with progression of atrophy, as has previously been shown for primary progressive aphasia or FTD subtypes combined.5 13 14 We found no association between baseline NfL and progression of GM atrophy. This evidence concerns the gene NEFL and primary progressive aphasia.