To develop and validate mathematical adjustment of serum neurofilament light chain (sNFL) for relevant confounders to strengthen its clinical utility

sNFL measured by advanced ultrasensitive immunoassays is rapidly becoming an important minimally-invasive biomarker reflecting neuro-axonal injury in neurological diseases. While sNFL correlates with cerebrospinal fluid NFL (cNFL), 40-60% of variance remains unexplained, offering an opportunity to explore what biological contributors are sources of this variance.

NFL was measured blindly in a prospective cohort of matched serum and CSF samples (n=1,138) collected from subjects with Multiple Sclerosis (MS, n=328), non-MS controls (n=199), and Healthy Volunteers (n=44) as part of a natural history protocol of neuroimmunological diseases (ClinicalTrials.gov Identifier:NCT00794352). All study participants gave informed consent. A set of clinical and laboratory biomarkers, neurological disability and severity scales, and imaging biomarkers of brain and upper cervical spinal cord (SC) injury were collected at the time of sample collection. Multiple linear regression (MLR) models were constructed in the training cohort to improve the cNFL-sNFL correlation, and the correlation between sNFL and clinical and imaging outcomes. The performance of these models was validated in an independent validation cohort.

Inclusion of age, blood urea nitrogen, alkaline phosphatase, creatinine, and weight in an MLR model improved correlation between sNFL and cNFL in the validation cohort from 57% of variance explained (R²) to 67%. This adjustment increased correlation of sNFL with contrast enhancing lesions (CEL, from R²=0.15 to R²=0.20). Only sNFL, but not cNFL correlated significantly with MS severity outcomes; we demonstrated that one of the reasons is release of NFL from peripheral nerves triggered by SC injury directly into serum.

The ability of sNFL to capture two sources of axonal injury (central, in the brain, and peripheral, reflecting SC injury that drives disability progression in MS) explains the stronger correlation of sNFL with MS severity outcomes.