NEFL and Alzheimer disease: Differences in mean levels of CSF NfL were assessed among the following four groups of CH participants: (1) normal AD biomarkers (A-T-N-, n = 87), (2) preclinical AD pathological change (A+T-N-, n = 42), (3) preclinical AD (A+T+/N±, n = 7) and (4) non-AD pathological change (A-T+/N+, n = 5).