NEFL and Alzheimer disease: In a cohort of Chinese participants, changes in CSF biomarker concentrations were observed over the 20 years preceding clinical diagnosis of sporadic AD, with specific timelines as follows: Aβ42 levels changed 18 years prior, Aβ42/Aβ40 ratio 14 years prior, p-tau181 11 years prior, t-tau 10 years prior, and NfL 9 years prior to diagnosis.