Myelin oligodendrocyte glycoprotein and aquaporin-4 antibodies are highly specific in children with acquired demyelinating syndromes.

AIM: Our objectives were to evaluate the utility of measuring myelin oligodendrocyte glycoprotein (MOG) and aquaporin-4 (AQP4) antibodies (Ab) in clinical practice and describe their associated neurological phenotypes in children. METHOD: Between 2012 and 2017, 371 children with suspected acquired demyelinating syndromes (ADS) seen in three tertiary centres were tested for MOG-Ab and AQP4-Ab. Medical notes were retrospectively reviewed, and clinical and demographic data compiled. Clinical phenotyping was performed blinded to the antibody results. RESULTS: After review, 237 of the 371 were diagnosed with ADS. Of these, 76 out of 237 (32.1%) were MOG-Ab positive and 14 out of 237 (5.9%) were AQP4-Ab positive. None were positive for both autoantibodies. All 134 patients with non-ADS were negative for MOG-Ab. MOG-Ab were identified in 45 out of 70 (64.3%) patients presenting with acute disseminated encephalomyelitis (ADEM) and in 24 out of 25 patients with relapsing ADEM. Thirty-six out of 75 (48%) MOG-Ab positive patients relapsed. Of the 33 children with neuromyelitis optic spectrum disorder, 14 were AQP4-Ab positive, 13 were MOG-Ab positive, and 6 were seronegative. Of the children with longitudinal samples, 8 out of 13 AQP4-Ab remained positive during the disease course compared to 35 out of 43 MOG-Ab (13/16 monophasic and 22/27 relapsing). INTERPRETATION: Myelin oligodendrocyte glycoprotein antibodies were identified in a third of children with ADS. Almost half of the MOG-Ab positive children relapsed and the majority of them remained antibody positive over 4-years follow-up. WHAT THIS PAPER ADDS: Myelin oligodendrocyte glycoprotein antibodies (MOG-Ab) are highly specific for acquired demyelinating syndromes (ADS). Myelin oligodendrocyte glycoprotein antibodies are not identified in children with peripheral demyelination or genetic leukodystrophies/hypomyelination. Up to 48% of MOG-Ab ADS paediatric patients relapse, higher than previously thought. Seroconversion to MOG-Ab negative status is infrequent; patients may test MOG-Ab positive at follow-up sampling even when asymptomatic. Myelin oligodendrocyte glycoprotein antibodies status should only be used in conjunction with the clinical information to guide maintenance therapy.

Significant, quantifiable differences exist between IgG subclass standards WHO67/97 and ERM-DA470k and can result in different interpretation of results.

OBJECTIVES: Accurate measurement of IgG subclass (IgGSc) levels are essential to aid in the diagnosis of disease states such as primary immunodeficiencies. However, there is no single standardisation of nephelometric and turbidimetric assays for these analytes and two reference materials have been utilised. We expand on previous reports and present data from a multi-site analysis that both identifies and quantitatively defines the differences in calibration resulting from the use of different reference materials. DESIGN AND METHODS: IgGSc antibodies in the serum specimens and reference materials were measured according to the manufacturers' instructions using commercially available IgGSc assays or components. RESULTS: Data from four independent sites showed that in spite of the different commercial suppliers of IgGSc assays calibrating to different reference materials, ERM-DA470k and WHO67 /97, the resulting calibrations were comparable for IgG1 and IgG2. However, for IgG3 and IgG4 the calibrations were significantly different. The use of assay specific normal ranges should compensate for these calibration differences, however, the two manufacturers' assays can give differing clinical classifications. The agreement between the different manufacturers' IgGSc assays was between 85.1% and 95.8% for all IgGSc assays, the discordance of sample classification for IgG1 and IgG2 assays was approximately 12% and 15% respectively, whilst that for IgG3 and IgG4 was 4% and 13% respectively. CONCLUSION: We discuss the similarities and differences between assays that utilise the different reference materials.