Objective: To analyze whether myelin oligodendrocyte glycoprotein antibody (MOG-Ab) titres at onset of the disease were different according to the clinical phenotype at presentation, and to investigate whether the titres were associated with risk of further relapses or predicted clinical outcome in adult patients. Finally, we assessed an alternative method to the classical measurement of MOG-Ab levels by serial dilutions.
Methods: This is a retrospective study including 79 MOG-Ab-positive adult patients, whose samples were obtained at first episode. MOG-Ab were tested by cell-based assay. HEK293 cells were transfected (tHEK293) with human-MOG plasmid. Non-tHEK293 cells were used as negative controls. Assessment of antibody titres was performed by serial dilution, and delta mean fluorescence intensity ratio signal (MOG-ratio ΔMFI) by flow cytometry. MOG-ratio ΔMFI was calculated as follows: (MFI tHEK293cells- MFI non-tHEK293cells)/MFI non-tHEK293cells. MOG-ratio ΔMFI was calculated from the first serum dilution at 1:320. The association between MOG-Ab titres and risk of relapse was analyzed by Cox regression. The association between MOG-Ab titres and visual or motor disability at last follow-up was performed by binary logistic regression. Poor visual outcome was defined when patients displayed some degree of visual disability (visual acuity [VA] < 20/20) and poor motor outcome when patients displayed some degree of motor disability (Disability Status Scale [DSS] > 1). We also investigated correlations between MOG-Ab titres and MOG-ratio ΔMFI.
Results: MOG-Ab titres were higher in Caucasians than in those with other ethnicities, and in patients with a more severe VA (VA ≤ 20/100) or motor disability (DSS ≥ 3.0) at onset (p = 0.006, 0.034, and 0.058, respectively). MOG-Ab titres were not associated with risk of relapses or with the final clinical outcome. MOG-ratio ΔMFI correlated with MOG-Ab titres in the whole cohort (ρ = 0.90; p < 0.001), and when stratified by initial clinical phenotype.
Conclusion: High MOG-Ab titres at onset are associated with a more severe presentation, but do not predict the future disease course. MOG-ratio ΔMFI is an alternative and straightforward method to determine MOG-Ab levels.
Keywords: MOG antibodies; Myelitis; Neuromyelitis optica; Optic neuritis; Prognosis; Titre.