Cerebrospinal fluid GAP-43 in early multiple sclerosis

Novel biomarkers identifying and predicting disease activity in multiple sclerosis (MS) would be valuable for primary diagnosis and as outcome measures for monitoring therapeutic effects in clinical trials. Axonal loss is present from the earliest stages of MS and correlates with disability measures. Growth-associated protein 43 (GAP-43) is a presynaptic protein with induced expression during axonal growth. We hypothesized this protein could serve as a biomarker of axonal regeneration capacity in MS.

We developed a novel GAP-43 enzyme-linked immunosorbent assay for quantification in cerebrospinal fluid (CSF) and measured GAP-43 levels in 71 patients with clinically isolated syndrome, 139 MS patients and 51 controls.

GAP-43 concentrations were similar in patients and controls. Nevertheless, GAP-43 levels were higher in patients with >10 T2-magnetic resonance imaging (MRI) lesions (p = 0.005). CSF GAP-43 concentrations correlated with CSF mononuclear cell counts (p = 0.031) and were inversely correlated with patient age (p = 0.038) with a trend for higher CSF GAP-43 concentrations in patients with gadolinium-enhancing MRI lesions and positive CSF oligoclonal immunoglobulin G status.

Our results suggest that axonal regeneration capacity is relatively preserved in early MS. CSF GAP-43 concentration is positively associated with markers of inflammation, suggesting possible inflammatory-driven expression of this growth-associated protein in early MS.