Also, while our findings support the use of serum NfL as a marker of neurodegeneration in AD, NfL is not a specific marker to AD and has been shown to increase in a number of other conditions, including HIV-associated dementia, PSP, FTD, and ALS.19,25,30,40 It may therefore be that serum NfL will be most useful for identifying and tracking AD-related neurodegeneration when combined with a test to confirm underlying AD molecular pathology, e.g., CSF tau/Aβ1-42 or amyloid PET. This evidence concerns the gene MAPT and Alzheimer disease.