Simpler and Reliable ALS Diagnosis Enabled With Blood Tests

Amyotrophic lateral sclerosis (ALS) is an adult onset fatal neurodegenerative syndrome characterized by the insidious onset of progressive motor symptoms and signs secondary to the loss of upper and lower motor neurons and their tracts.

Neurofilaments are neuron-specific cytoskeletal intermediate filament heteropolymers composed of neurofilament light chain (NFL), NF medium chain, and NF heavy chain (NFH) in combination with either α-internexin in the central nervous system or peripherin in the peripheral nervous system.

Clinical Scientists from the University of Gothenburg (Gothenburg, Sweden) and Umeå University (Umeå, Sweden) retrospectively quantified cerebrospinal fluid (CSF) NFL, CSF phosphorylated neurofilament heavy chain (pNFH) and plasma NFL in stored samples that were collected at the diagnostic work-up of 234 ALS patients, 44 ALS mimics, and nine controls. The team assessed the diagnostic performance, prognostication value and relationship to the site of onset and genotype.

CSF NFL concentrations were analyzed with a validated ELISA with intra- and interplate variations of < 8% and < 13%, respectively. CSF NFL analyses were performed in duplicates. Two control samples were not analyzed for CSF NFL due to the limited CSF volume. CSF pNFH concentrations were measured with an in-house-developed ELISA with minor modifications with intra- and interplate variations of < 3.9% and < 9.4%, respectively. Regarding CSF pNFH analyses, 226 samples were evaluated in singlicates due to the limited CSF volume. Plasma NFL concentrations were measured using a single-molecule array (SIMOA) assay on an HD-1 Analyzer (Quanterix, Billerica, MA, USA) with intra- and interplate variations of < 10% and < 12%, respectively.

The investigators reported that CSF NFL, CSF pNFH and plasma NFL levels were significantly increased in ALS patients compared to patients with neuropathies and myelopathies, patients with myopathies and controls. Furthermore, CSF pNFH and plasma NFL levels were significantly higher in ALS patients than in patients with other MNDs. Bulbar onset ALS patients had significantly higher plasma NFL levels than spinal onset ALS patients. ALS patients with C9orf72HRE mutations had significantly higher plasma NFL levels than patients with SOD1 mutations. Survival was negatively correlated with all three biomarkers.

Arvin Behzadi, a doctoral student and first author of the study, said, “Finding suspected cases of ALS through a blood test opens up completely new opportunities for screening and measuring neurofilaments in blood collected longitudinally enables easier quantification of treatment effects in clinical drug trials compared to longitudinal collection of CSF. Finding ALS early in the disease course may facilitate earlier administration of pharmaceutical treatment, before the muscles have atrophied.”

The authors concluded that all three biomarkers are of clinical value in affirming an ALS diagnosis and excluding potential ALS mimics. CSF pNFH showed the highest AUC in terms of differentiating ALS from ALS mimics. Plasma NFL analysis has the advantage that it does not require a lumbar puncture, has only a minimal difference in diagnostic performance compared to CSF NFL levels and shows the highest AUC in terms of prognosticating ALS short and long survival. The study was originally on November 11, 2021 in the journal Scientific Reports.

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