Potential Prognostic Biomarker for ALS Identified

Megan Brooks

December 07, 2012

Phosphorylated neurofilament heavy subunit (pNF-H) is a potential prognostic biomarker in amyotrophic lateral sclerosis (ALS), researchers say.

In patients with ALS, increased pNF-H concentrations in peripheral blood, and in cerebrospinal fluid (CSF) as shown previously, were associated with faster rate of disease progression and shorter survival from the time of sample collection.

The findings suggest that pNF-H levels in peripheral blood may be an indicator of disease activity and prognosis in ALS, the researchers say.

"Measurement of pNF-H in peripheral blood warrants further study in comparison with CSF in future studies of pNF-H as a putative prognostic biomarker in ALS," Kevin B. Boylan, MD, Department of Neurology, Mayo Clinic, Jacksonville, Florida, told Medscape Medical News.

The research was published online in the Journal of Neurology, Neurosurgery and Psychiatry.

Critical Need

"This study is significant because there are no validated biomarkers for ALS and they are badly needed," Steven Finkbeiner, MD, PhD, from the Gladstone Institute of Neurological Disease in San Francisco, California, who was not involved in the study, told Medscape Medical News.

"Imaging has proven to be very promising for other neurodegenerative diseases, but the evidence so far is that it may not be as promising as a biomarker for ALS. So, developing blood or CSF tests that can be reliable biomarkers [in ALS] is really critical," Dr. Finkbeiner added.

ALS is a progressive neurodegenerative disease that affects nerve cells in the brain and spinal cord that control voluntary muscle movement. The rate of progression varies widely among patients, and survival from the date of diagnosis can be a few months to 10 years or more.

"Many ALS researchers have been trying to develop a molecular biomarker test for nerve damage like this, and we are encouraged that this test shows such promise," Dr. Boylan said in a statement from Mayo Clinic.

Dr. Kevin B. Boylan

The researchers used the ALS Functional Rating Scale (ALSFRS-R) to evaluate the association between pNF-H level in peripheral blood, serum, and CSF and disease progression in 63 patients with ALS from 3 cohorts: 20 patients followed for 4 and 12 months (12-month cohort), 20 patients followed for 4 months only (4-month cohort), and 23 patients for whom the researchers had survival data but not serial ALSFS-R data.

Faster Slope of Decline

In the 12-month cohort, the association between higher CSF pNF-H level and faster rate of decline in the ALSFRS-R was significant after 4 months (P = .006) and at 12 months (P = .015). The association between higher serum pNF-H level and more rapid decline in the ALSFRS-R was significant after 4 months (P = .042) but not after 12 months (P = .019).

In the 12-month cohort, higher plasma pNF-H level was weakly associated with faster decline in the ALSFRS-R at 4 months (P = .095) and less so over 12 months (P = .29). However, when the 4-month cohort was included in this analysis, the association between higher plasma pNF-H level and more rapid decline in the ALSFRS-R was statistically significant (P = .030).

The researchers also examined plasma and serum pNF-H levels in relation to survival from date of sample collection. They found that a doubling of pNF-H in plasma was associated with a nearly 2-fold increase in the risk for death at the end of follow-up (hazard ratio [HR], 1.87; 95% confidence interval [CI], 1.19 - 3.35; P = .006), whereas a doubling of pNF-H in serum was associated with a greater than 2-fold estimated increase in the risk for death (HR, 2.10; 95% CI, 1.28 - 3.91; P = .002).

A similar relationship emerged for plasma pNF-H in the 4-month cohort and in all 3 cohorts combined. The evidence for a relationship of higher CSF pNF-H and shorter survival was weaker.

"The observation that pNF-H levels in peripheral blood or CSF are associated with clinical outcomes months later implies that pNF-H levels do not fluctuate widely over time intervals on the order of a few months," Dr. Boylan said, "but more information on this is needed."

Earlier work by Dr. Boylan and colleagues suggests that plasma pNF-H levels in ALS are relatively stable over 4 months, but this requires confirmation in larger numbers of patients in blood and CSF collected serially over longer periods. "We are looking at this now," Dr. Boylan said. Efforts to improve the sensitivity of the neurofilament assay used in the study are also underway.

Implications for ALS Trials

The study also suggests that plasma pNF-H concentrations may be higher in patients with bulbar-onset as opposed to spinal-onset ALS; this finding requires further study, the researchers say. It is "interesting that patients with bulbar onset had levels 2- to 3-fold higher than those with spinal onset," Dr. Finkbeiner commented.

This protein may have prognostic value, "if these data are replicated by others and prove to be robust," Dr. Finkbeiner said. "In the absence of a therapy, better prognostic data can be helpful to patients and families for planning purposes."

But Dr. Finkbeiner said its most important potential value may lie in improving the design of clinical trials.

"A big challenge in ALS is that there is quite a bit of variability in the rate of disease progression. The more variability there is in the course of a disease, the more difficult it is to do a successful clinical trial because the variability increases the likelihood that any apparent differences associated with treatment are due to chance," he explained.

"To overcome this problem, the trial has to go on for a longer period of time and enroll more patients, which all adds cost and potential safety risk. If this biomarker proves valid, it might be possible to identify a subset of ALS patients whose disease can be expected to progress more uniformly, which would make the detection of treatment effects easier and cheaper," Dr. Finkbeiner told Medscape Medical News.

"Besides the usual imperfections of biomarkers," he added, "the study had a relatively small number of patients, and the biomarker literature is replete with reports of observations that could not be reproduced by other groups. It's encouraging that this was a multisite effort, but replication with larger groups of patients by independent investigators will be critical."

The study was funded by the ALS Association, the Packard Center for ALS Research, MCF ALS Center Donor Funds, and Mayo Foundation. Dr. Boylan receives research support from the ALS Association, Biogen Idec, Cytokinetics Inc, Neuraltus Pharmaceuticals, the National Institutes of Health, and Mayo Foundation. Gerry Shaw, PhD, the study's senior author, developed the neurofilament assay used in the study. Dr. Finkbeiner has disclosed no relevant financial relationships.

J Neurol Neurosurg Psychiatry. Published online October 31, 2012. Abstract