A retrospective, longitudinal study of patients with different clinical subtypes of ALS supports the value of neurofilament light chain (NfL) as a biomarker for disease progression. In the work, published March 6 in JAMA Neurology, Gianni Sorarù and colleagues at the University of Padua in Padova, Italy, detail a strong correlation between cerebrospinal fluid NfL and rapid progression or shorter survival in a group of 94 patients. NfL fared less well as a diagnostic marker. The researchers found significant overlap in NfL levels among patients with ALS, frontotemporal dementia (FTD), and other motor neuronopathies.

 “This study supports previous findings that NfL is elevated in ALS and FTD, and provides solid data on NfL in different types of ALS,” said Lucie Bruijn of the ALS Association, Washington, D.C. “Perhaps most important, the work confirms that NfL could be an important tool for distinguishing fast and slow progressors. For that reason, it could be a good stratifying measure in clinical trials,” Bruijn said. She added that the study adds some important details about NfL, including showing that levels are not affected by sex or age. 

When axons fall apart, they release neurofilament protein, which scientists are pursuing as a biomarker for neurodegeneration in many diseases. Researchers first reported a marked elevation of NfL in the cerebrospinal fluid (CSF) of patients with amyotrophic lateral sclerosis two decades ago (Rosengren et al., 1996). Subsequent work established that high CSF or blood levels of NfL tracked with poorer prognosis and shorter survival (see Jun 2015 news; Weydt et al., 2016; Steinacker et al., 2016). 

To ask whether NfL might be diagnostically useful, first author Alexandra Gaiani and colleagues analyzed CSF collected from 176 patients in Padua between 2010 and 2016. The group included the 94 patients diagnosed with ALS, 20 with FTD, 18 with motor neuropathies, and 44 controls. Each CSF sample was obtained between six months and two years after disease onset and stored. All were analyzed for NfL in 2016.  

As expected, the ALS group had significantly higher CSF NfL than the other motor neuropathies or the control group. The FTD patients had intermediate levels. NfL in ALS and FTD had previously only been studied separately, Sorarù told Alzforum.

The researchers further divided the ALS patients into typical ALS (58 subjects), flail arm or flail leg syndrome (11 patients), progressive muscular atrophy (PMA, 9), progressive bulbar palsy (PBP, 9), and upper motor neuron dominant ALS (UMND, 7). The highest NfL levels occurred in patients with traditional ALS and in variants associated with upper motor neuron degeneration (progressive bulbar palsy and upper motor neuron dominant ALS). Only modest elevations accompanied the clinically milder forms (flail arm or flail leg syndrome and progressive muscular atrophy), which involve mainly lower motor neurons.

Those results harken back to the original 1996 report in which researchers already noted a difference in neurofilament in upper and lower motor neuron forms of the disease (see also Brettschneider et al., 2012). More recently, diffusion tensor imaging, which measures the integrity of large axons, has directly linked degradation of upper motor neurons in the corticospinal tract to the rise in NfL in ALS (Menke et al., 2015). 

What about prognosis? The researchers followed patients for up to 80 months after their lumbar puncture. In agreement with previous findings, NfL concentration in the CSF inversely correlated with speed of disease progression as well as with overall survival, even after adjusting for sex, age, ALS subtype, and disease duration.

UMND ALS presented the one exception to the rule. Although it is mild and slow-progressing, patients with this form had CSF NfL as high as typical ALS. The authors speculated this reflects the predominantly upper corticospinal tract breakdown in UMND ALS.

Could NfL be useful for diagnosis? Based on their numbers, the authors suggest NfL on its own can distinguish ALS from controls with nearly 90 percent sensitivity and specificity. However, the marker cannot distinguish ALS from FTD or other motor neuron disease with such certainty.  

“I’m less convinced about the diagnostic part of their study, but I think the evidence that correlates NfL to survival is very strong,” said Merit Cudkowicz, Harvard Medical School.  “Because they studied a large number of people with motor neuron disease, they have more power to show the spread of neurofilament values, and its strength as a good prognostic marker.” Cudkowicz pointed out that in cases of lower motor neuron involvement, clinicians don't know if patients will stay that way or develop classical ALS. “A lower NfL value at the beginning is a good prognostic sign,” she said.

The tight link to progression means that NfL could help clinicians select subjects for clinical trials. “If you take all comers, you get huge variability in how people progress, and then you need large sample sizes to see any effects,” noted Cudkowicz. That’s a big challenge for the field, she added. “If NfL could help pick a group of people who, for example, are progressing at a similar rate, we might be able to run smaller and faster trials,” she said.

 “The study is really strong and well-conducted,” said Henrik Zetterberg, University of Gothenberg, Sweden. By replicating previous studies, it makes the case for NfL in ALS even stronger, he said.

The latest development in the field, a very sensitive blood test for NfL based on single molecule array analysis, should expand the reach of the test to many more people, and allow for easier, repeat, longitudinal analysis, noted Zetterberg (see Feb 2017 news).—Pat McCaffrey

Pat McCaffrey is a writer based in Newton, Massachusetts.


  1. This is a nice confirmation of earlier prospective studies of neurofilaments in motor neuron diseases (Lu et al., 2015; Steinacker et al. 2016). The measurement of the light chain in CSF is often a bit tricky because of assay variations. We could observe this in our round robin on neurofilaments (Oeckl et al., 2016). Therefore, in our clinical routine we use both neurofilament light chain and phosphorylated heavy chain. For ALS and other motor neuron diseases, such as primary lateral sclerosis (PLS), this might not make a big difference (see Steinacker et al. 2016). However, it allows a direct confirmation of the quality of the measurements. Interestingly, for primary progressive aphasias (PPA), one can subtype specific differences in neurofilament light chain and phosphorylated heavy chain measurements (Steinacker et al., 2017).


    . Neurofilament light chain: A prognostic biomarker in amyotrophic lateral sclerosis. Neurology. 2015 Jun 2;84(22):2247-57. Epub 2015 May 1 PubMed.

    . Neurofilaments in the diagnosis of motoneuron diseases: a prospective study on 455 patients. J Neurol Neurosurg Psychiatry. 2016 Jan;87(1):12-20. Epub 2015 Aug 21 PubMed.

    . Multicenter validation of CSF neurofilaments as diagnostic biomarkers for ALS. Amyotroph Lateral Scler Frontotemporal Degener. 2016 Jul-Aug;17(5-6):404-13. Epub 2016 Apr 11 PubMed.

    . Neurofilament as a blood marker for diagnosis and monitoring of primary progressive aphasias. Neurology. 2017 Mar 7;88(10):961-969. Epub 2017 Feb 8 PubMed.

  2. This is a nice confirmation of the 1996 Rosengren et al. study that reported that patients with amyotrophic lateral sclerosis and other neurodegenerative diseases have increased levels of neurofilament protein in CSF.

    In agreement with that paper, Gaiani and colleagues also found higher NfL levels in ALS subtypes with upper motor neuron involvement as compared with lower motor neuron disease. Thus, this paper further supports the use of CSF biomarkers in the evaluation of patients in clinical neurology.

    Interestingly, for this specific biomarker, technical developments have given the possibility to accurately analyze NfL also in blood samples (Gisslén et al., 2015), with plasma levels showing a tight correlation with CSF levels (Gisslén et al., 2015; Kuhle et al., 2016). 

    The first studies show increased blood levels of NfL in both ALS (Gaiottino et al., 2013) and FTD (Rohrer et al., 2016), similar to the findings in CSF in the Gaiani study.


    . Patients with amyotrophic lateral sclerosis and other neurodegenerative diseases have increased levels of neurofilament protein in CSF. J Neurochem. 1996 Nov;67(5):2013-8. PubMed.

    . Plasma Concentration of the Neurofilament Light Protein (NFL) is a Biomarker of CNS Injury in HIV Infection: A Cross-Sectional Study. EBioMedicine. 2016 Jan;3:135-40. Epub 2015 Nov 22 PubMed.

    . Comparison of three analytical platforms for quantification of the neurofilament light chain in blood samples: ELISA, electrochemiluminescence immunoassay and Simoa. Clin Chem Lab Med. 2016 Oct 1;54(10):1655-61. PubMed.

    . Increased neurofilament light chain blood levels in neurodegenerative neurological diseases. PLoS One. 2013;8(9):e75091. PubMed.

    . Serum neurofilament light chain protein is a measure of disease intensity in frontotemporal dementia. Neurology. 2016 Sep 27;87(13):1329-36. Epub 2016 Aug 31 PubMed.

  3. This study adds further weight to CSF NfL as the leading prognostic biomarker in ALS. The extension of the analysis to consider clinical upper and lower motor neuron involvement, regional phenotypes, and the clinical disease stage is interesting, and the correlations seem likely to largely reflect the underlying rate of disease progression in each sub-group.

    CSF NfL should now be a standard part of all future therapeutic trials, to understand its practicality and performance in this landscape, compared to standard disability measures. A routine diagnostic role for CSF NfL is still uncertain. It is not a biomarker specific to ALS, and true mimic disorders are relatively uncommon for the experienced ALS neurologist, for whom clinical history and examination are still the most accurate. Blood-based NfL assay development is also anticipated, which would remove a significant practical barrier to wider implementation.

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News Citations

  1. Blood Marker May Predict ALS Progression
  2. Touchdown for NfL: Blood Test Tells Parkinson's from Related Disorders

Paper Citations

  1. . Patients with amyotrophic lateral sclerosis and other neurodegenerative diseases have increased levels of neurofilament protein in CSF. J Neurochem. 1996 Nov;67(5):2013-8. PubMed.
  2. . Neurofilament levels as biomarkers in asymptomatic and symptomatic familial amyotrophic lateral sclerosis. Ann Neurol. 2016 Jan;79(1):152-8. Epub 2015 Dec 17 PubMed.
  3. . Neurofilaments in the diagnosis of motoneuron diseases: a prospective study on 455 patients. J Neurol Neurosurg Psychiatry. 2016 Jan;87(1):12-20. Epub 2015 Aug 21 PubMed.
  4. . Axonal damage markers in cerebrospinal fluid are increased in ALS. Neurology. 2006 Mar 28;66(6):852-6. PubMed.
  5. . CSF neurofilament light chain reflects corticospinal tract degeneration in ALS. Ann Clin Transl Neurol. 2015 Jul;2(7):748-55. Epub 2015 May 25 PubMed.

Further Reading

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Primary Papers

  1. . Diagnostic and Prognostic Biomarkers in Amyotrophic Lateral Sclerosis: Neurofilament Light Chain Levels in Definite Subtypes of Disease. JAMA Neurol. 2017 May 1;74(5):525-532. PubMed.