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Plasma levels of neurofilament light track neurodegeneration in MCI and Alzheimer’s disease

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Neurofilament could shed light on why trials fail - or succeed

This is an impressive study that convincingly demonstrates the sensitivity of plasma neurofilament light (NfL) to disease progression in patients with mild cognitive impairment and dementia in the Alzheimer’s Disease Neuroimaging Initiative cohort.

It is known that NfL is sensitive to neuronal damage that can result from a variety of pathologies, not limited to Alzheimer’s disease, so it is not diagnostically specific. In the present study there was even overlap of values between the cognitively unimpaired and mild cognitive impairment groups at baseline as well, although the levels separated over time.

In the right setting, NfL might still be a clinically useful diagnostic marker, especially for mild-stage disease when other clinical measures such as mental status scores and structural brain scans are inconclusive, and further study seems warranted for such a possibility.

Its greatest utility, however, will likely be in clinical trials. It would have been of the greatest interest to know how NfL levels changed in the setting of demonstrated cerebral amyloid clearance by agents such as aducanumab that failed to halt dementia progression, or in the setting of BACE1 inhibitor-related worsening of cognition. Did NfL levels remain static in the former and rise in the latter? Looking ahead, it seems likely that this easily accessed biomarker will become an integral part of clinical trial design. Assuming cost is not overly burdensome, it may even find its way eventually into clinical practice.

Dr. Caselli is professor of neurology at the Mayo Clinic Arizona in Scottsdale and associate director and clinical core director of the Arizona Alzheimer’s Disease Center.



Neurofilament light (NfL) levels in plasma appear to track cognitive decline in dementia, as well as cortical thinning and hippocampal atrophy that accompany progression from normal cognition to mild cognitive impairment (MCI) to Alzheimer’s disease.

Plasma levels of the axonal protein also correlated with its presence in cerebrospinal fluid, and mirrored the changes in amyloid beta (Abeta) 42, Niklas Mattsson, MD, and colleagues wrote in JAMA Neurology.

“Taken together, these findings suggest that the neurofilament light level is a dynamic biomarker that changes throughout the course of Alzheimer’s disease and is sensitive to progressive neurodegeneration,” wrote Dr. Mattsson of Lund (Sweden) University and his coauthors. “This has important implications, given the unmet need for noninvasive blood-based methods to objectively track longitudinal neurodegeneration in Alzheimer’s disease.”

A blood-based biomarker of Alzheimer’s disease progression could open a new door for drug trials, the authors noted. Previously, NfL levels have only been available by lumbar puncture – a invasive and expensive test that many patients resist. If NfL plasma levels do reliably track dementia progression, the test could become a standard part of clinical trials, providing regular drug response data as the study progresses.

Neurofilaments are polypeptides that give structure to the neuronal cytoskeleton and regulate microtubule function. Injured cells release the protein very quickly. Neurofilaments are elevated in traumatic brain injury, multiple sclerosis, and some psychiatric illnesses. Neurofilament levels have even been used to predict neurologic recovery after cardiac arrest.

Dr. Mattsson and his team used data obtained over 11 years from 1,583 subjects enrolled in the Alzheimer’s Disease Neuroimaging Initiative study. The sample comprised three groups: cognitively unimpaired controls (401), patients with MCI (855), and patients with Alzheimer’s dementia (327). The investigators analyzed 4,326 samples.

In addition to the NfL measurements, they tracked Abeta and tau in cerebrospinal fluid (CSF), structural brain changes by 18fluorodeoxyglucose (FDG)–PET and MRI, and cognitive and functional performance. The primary outcome was NfL’s association with these changes. The team set the lower limit of NfL as 6.7 ng/L and the upper, 1,620 ng/L.

At baseline, only advancing age correlated with NfL levels. But it was significantly higher in patients with MCI (37.9 ng/L) and Alzheimer’s dementia (45.9 ng/L) than it was in the control subjects (32.1 ng/L). Over the years of follow-up, levels increased in all groups, but NfL increased more rapidly among patients with MCI and Alzheimer’s dementia than controls (2.7 vs. 2.4 ng/L per year). The difference was most pronounced when comparing levels in patients with Alzheimer’s dementia and MCI with controls. However, control subjects who were Abeta positive by CSF had greater NfL changes than Abeta-negative controls.

Baseline measures of CSF Abeta and tau, as well as hippocampal and ventricular volume and cortical thickness, also correlated with NfL levels, as did cognition and functional scores.

During follow-up, the diagnostic groups showed different NfL trajectories, which correlated strongly with the other measures.

In the control group, NfL increases correlated with lower FDG-PET measures, lower CSF Abeta, reduced hippocampal volume, and higher ventricular volume. Among patients with MCI, NfL increases correlated most strongly with hippocampal volume, temporal region, and cognition. Among patients with Alzheimer’s dementia, the NfL increase most strongly tracked cognitive decline,

When the investigators applied these findings to the A/T/N (amyloid, tau, neurodegeneration) classification system, NfL most often correlated with neurodegeneration, but not always. This might suggest that the neuronal damage occurred separately from Abeta changes. In all three groups, rapid NfL increases mirrored the rate of change in most other measures.

“In controls and patients with MCI and Alzheimer’s dementia, greater rates of NfL were associated with accelerated reduction in FDG-PET measures … expansion of ventricular volume,” and a reduction in cognitive and functional performance, Dr. Mattsson and his colleagues wrote.“ In addition, greater increases in NfL levels were associated with accelerated loss of hippocampal volume and entorhinal cortical thickness in controls and patients with MCI and with accelerated increases in total tau level, phosphorylated tau level, and white matter lesions in patients with MCI. In general, the concentrations of blood-based NfL appears to reflect the intensity of the neuronal injury.”

Dr Mattsson reported being a consultant for the Alzheimer’s Disease Neuroimaging Initiative.

SOURCE: Mattsson N et al. JAMA Neurol. 2019 Apr 22. doi: 10.1001/jamaneurol.2019.0765.

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