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Original Investigation
April 22, 2019

Association Between Longitudinal Plasma Neurofilament Light and Neurodegeneration in Patients With Alzheimer Disease

Author Affiliations
  • 1Clinical Memory Research Unit, Department of Clinical Sciences, Lund University, Lund, Sweden
  • 2Department of Neurology, Skåne University Hospital, Sweden
  • 3Wallenberg Center for Molecular Medicine, Lund University, Lund, Sweden
  • 4Department of Neurology, Perelman School of Medicine, University of Pennsylvania, Philadelphia
  • 5Institute of Neuroscience and Physiology, Department of Psychiatry and Neurochemistry, the Sahlgrenska Academy at the University of Gothenburg, Mölndal, Sweden
  • 6Clinical Neurochemistry Laboratory, Sahlgrenska University Hospital, Mölndal, Sweden
  • 7Department of Neurodegenerative Disease, University College London Institute of Neurology, Queen Square, London, United Kingdom
  • 8UK Dementia Research Institute at University College London, London, United Kingdom
JAMA Neurol. Published online April 22, 2019. doi:10.1001/jamaneurol.2019.0765
Key Points

Question  Is there an association between longitudinal plasma neurofilament light and hallmarks of Alzheimer disease?

Findings  In this cohort study of 1583 individuals in the multicenter Alzheimer’s Disease Neuroimaging Initiative study, longitudinal plasma neurofilament light level increased in association with several baseline and longitudinal hallmarks of Alzheimer disease. The increase in plasma neurofilament light level was associated with changes in other established measures of neurodegeneration in Alzheimer disease.

Meaning  The findings suggest that plasma neurofilament light can be used as a noninvasive biomarker to track neurodegeneration in patients with Alzheimer disease.

Abstract

Importance  Plasma neurofilament light (NfL) has been suggested as a noninvasive biomarker to monitor neurodegeneration in Alzheimer disease (AD), but studies are lacking.

Objective  To examine whether longitudinal plasma NfL levels are associated with other hallmarks of AD.

Design, Setting, and Participants  This North American cohort study used data from 1583 individuals in the multicenter Alzheimer’s Disease Neuroimaging Initiative study from September 7, 2005, through June 16, 2016. Patients were eligible for inclusion if they had NfL measurements. Annual plasma NfL samples were collected for up to 11 years and were analyzed in 2018.

Exposures  Clinical diagnosis, Aβ and tau cerebrospinal fluid (CSF) biomarkers, imaging measures (magnetic resonance imaging and fluorodeoxyglucose–positron emission tomography), and tests on cognitive scores.

Main Outcomes and Measures  The primary outcome was the association between baseline exposures (diagnosis, CSF biomarkers, imaging measures, and cognition) and longitudinal plasma NfL levels, analyzed by an ultrasensitive assay. The secondary outcomes were the associations between a multimodal classification scheme with Aβ, tau, and neurodegeneration (ie, the ATN system) and plasma NfL levels and between longitudinal changes in plasma NfL levels and changes in the other measures.

Results  Of the included 1583 participants, 716 (45.2%) were women, and the mean (SD) age was 72.9 (7.1) years; 401 had no cognitive impairment, 855 had mild cognitive impairment, and 327 had AD dementia. The NfL level was increased at baseline in patients with mild cognitive impairment and AD dementia (mean levels: cognitive unimpairment, 32.1 ng/L; mild cognitive impairment, 37.9 ng/L; and AD dementia, 45.9 ng/L; P < .001) and increased in all diagnostic groups, with the greatest increase in patients with AD dementia. A longitudinal increase in NfL level correlated with baseline CSF biomarkers (low Aβ42 [P = .001], high total tau [P = .02], and high phosphorylated tau levels [P = .02]), magnetic resonance imaging measures (small hippocampal volumes [P < .001], thin regional cortices [P = .009], and large ventricular volumes [P = .002]), low fluorodeoxyglucose–positron emission tomography uptake (P = .01), and poor cognitive performance (P < .001) for a global cognitive score. With use of the ATN system, increased baseline NfL levels were seen in A–T+N+ (P < .001), A+T–N+ (P < .001), and A+T+N+ (P < .001), and increased rates of NfL levels were seen in A–T+N– (P = .009), A–T+N+ (P = .02), A+T–N+ (P = .04), and A+T+N+ (P = .002). Faster increase in NfL levels correlated with faster increase in CSF biomarkers of neuronal injury, faster rates of atrophy and hypometabolism, and faster worsening in global cognition (all P < .05 in patients with mild cognitive impairment; associations differed slightly in cognitively unimpaired controls and patients with AD dementia).

Conclusions and Relevance  The findings suggest that plasma NfL can be used as a noninvasive biomarker associated with neurodegeneration in patients with AD and may be useful to monitor effects in trials of disease-modifying drugs.

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