Serum GFAP and NfL as disease severity and prognostic biomarkers in patients with aquaporin-4 antibody-positive neuromyelitis optica spectrum disorder

Patrick Schindler, Ulrike Grittner, Johanna Oechtering, David Leppert, Nadja Siebert, Ankelien S. Duchow, Frederike C. Oertel, Susanna Asseyer, Joseph Kuchling, Hanna G. Zimmermann, Alexander U. Brandt, Pascal Benkert, Markus Reindl, Sven Jarius, Friedemann Paul, Judith Bellmann-Strobl, Jens Kuhle, Klemens Ruprecht

Neuromyelitis optica spectrum disorder (NMOSD) is a frequently disabling neuroinflammatory syndrome with a relapsing course. Blood-based disease severity and prognostic biomarkers for NMOSD are a yet unmet clinical need. Here, we evaluated serum glial fibrillary acidic protein (sGFAP) and neurofilament light (sNfL) as disease severity and prognostic biomarkers in patients with aquaporin-4 immunoglobulin (Ig)G positive (AQP4-IgG+) NMOSD. sGFAP and sNfL were determined by single-molecule array technology in a prospective cohort of 33 AQP4-IgG+ patients with NMOSD, 32 of which were in clinical remission at study baseline. Sixteen myelin oligodendrocyte glycoprotein IgG-positive (MOG-IgG+) patients and 38 healthy persons were included as controls. Attacks were recorded in all AQP4-IgG+ patients over a median observation period of 4.25 years. In patients with AQP4-IgG+ NMOSD, median sGFAP (109.2 pg/ml) was non-significantly higher than in MOG-IgG+ patients (81.1 pg/ml; p = 0.83) and healthy controls (67.7 pg/ml; p = 0.07); sNfL did not substantially differ between groups. Yet, in AQP4-IgG+, but not MOG-IgG+ patients, higher sGFAP was associated with worse clinical disability scores, including the Expanded Disability Status Scale (EDSS, standardized effect size = 1.30, p = 0.007) and Multiple Sclerosis Functional Composite (MSFC, standardized effect size = - 1.28, p = 0.01). While in AQP4-IgG+, but not MOG-IgG+ patients, baseline sGFAP and sNfL were positively associated (standardized effect size = 2.24, p = 0.001), higher sNfL was only non-significantly associated with worse EDSS (standardized effect size = 1.09, p = 0.15) and MSFC (standardized effect size = - 1.75, p = 0.06) in patients with AQP4-IgG+ NMOSD. Patients with AQP4-IgG+ NMOSD with sGFAP > 90 pg/ml at baseline had a shorter time to a future attack than those with sGFAP ≤ 90 pg/ml (adjusted hazard ratio [95% confidence interval] = 11.6 [1.3-105.6], p = 0.03). In contrast, baseline sNfL levels above the 75th age adjusted percentile were not associated with a shorter time to a future attack in patients with AQP4-IgG+ NMOSD. These findings suggest a potential role for sGFAP as biomarker for disease severity and future disease activity in patients with AQP4-IgG+ NMOSD in phases of clinical remission.