Roles of cerebrospinal fluid metabolites in neuromyelitis optica spectrum disorder: Insights from Mendelian randomization

Neuromyelitis optica spectrum disorder (NMOSD) is a rare multifocal inflammatory disease that primarily affects the optic nerve and spinal cord, leading to visual loss and paralysis. Although current research has identified numerous biomarker changes in the cerebrospinal fluid (CSF), the causal relationships between these changes and NMOSD are not yet fully understood, and they are susceptible to confounding factors. In this study, Mendelian randomization (MR) analyses were conducted to estimate the role of CSF metabolites in aquaporin-4 (AQP4)-IgG positive and AQP4-IgG negative NMOSD. We strictly adhered to the 3 principles of MR when selecting instrumental variables, effectively reducing the impact of confounding variables. Additionally, we conducted a comprehensive and meticulous sensitivity analysis to ensure the robustness of positive outcomes. We have elucidated the roles of several CSF metabolites in NMOSD, with specific glycerophosphocholine species showing risk associations in AQP4-IgG positive and AQP4-IgG negative subtypes, while ascorbate and N-acetylhexosamines demonstrate protective effects across both subtypes, thereby providing valuable insights. No evidence of heterogeneity or horizontal pleiotropy was observed in MR analyses. These metabolites hold the potential to inform pathogenesis and guide the development of therapeutic strategies for these conditions.