Serum Neurofilament light (sNFL) protein is the most promising marker of disease activity and treatment response in Multiple Sclerosis (MS). To implement sNFL in clinical practice, the definition of normal widely accepted values represents a crucial step still to be addressed. Clinically applicable cut-off values need to take into account age dependency; in addition, recent evidences suggest that physical parameters as body mass index (BMI) and blood volume (BV) might influence sNFL levels.
The present study aims to address these crucial needs, describing sNFL levels in healthy population, their inter-individual variability in a short-term follow-up and defining reference cut-off values. The final objective is to define a strategy to allow implementation of sNFL in clinical practice.
We measured sNFL by single molecule array (Simoa) assay (NF-light advantage Kit, Quanterix) in 79 healthy individuals to define reference cut-off values. Age, BMI and BV were correlated with sNFL levels. In addition, sNFL were evaluated after a short-term follow-up time (median 67 days) to assess intra-individual variability: consecutive blood samples were tested in a subset of 27 participants (n=2-4 sample for each individual) and the coefficient of variation (CV) for NFL levels of each participant was evaluated.
sNFL were also tested in 23 naïve MS patients both at diagnostic time and immediately before treatment (median 76 days after) to evaluate the variability of sNFL in patients and the applicability of obtained cut-off values.
1) Our data confirmed a strong correlation between sNFL levels and age. We found a negative correlation between sNFL levels and BV. 2) Short-term follow-up NFL assessments showed an overall intra-individual stability in sNFL levels in healthy population (median CV 15%). 3) We defined specific age decade-related cut-off values. 4) In naïve MS patients, sNFL levels were higher than control values; a high variability between diagnostic time and the beginning of treatment (median CV 39%) was shown. Cut-off values were applied in MS patients to discriminate high from normal sNFL levels: at diagnostic time, 57% of MS patients showed high sNFL levels, while at treatment start, 70% of patients demonstrated normal NFL values.
The present study suggests a strategy to define clinical applicable cut-offs to exploit sNFL as a personalised medicine tool in MS: specific cut-off values were calculated for each age decade. sNFL levels demonstrated an overall intra-individual stability in healthy participants in the short-term: this is relevant for a biomarker of disease activity and treatment response that, if successful, will be serially assessed during patients follow-up.