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Myelin oligodendrocyte glycoprotein and aquaporin‐4 antibodies in children with acquired demyelinating syndromes

Myelin oligodendrocyte glycoprotein (MOG) and aquaporin-4 (AQP4) antibodies have recently gained attention in children with acquired demyelinating syndromes (ADS). Previously, MOG antibodies were mainly thought to play an important role in the pathogenesis of multiple sclerosis. But recent studies have shown that MOG antibodies are also found in children with monophasic episodes such as optic neuritis (ON), acute disseminated encephalomyelitis (ADEM), or recurrent events including AQP4-negative neuromyelitis optica spectrum disorder (NMOSD) or ADEM-ON that are distinct from multiple sclerosis in regards to several clinical and neuroradiological aspects. On the other hand, AQP4 antibodies have been found in a more distinct subgroup of children summarized under the umbrella of NMOSD, which has facilitated the accurate diagnosis and initiation of treatment. Duignan et al. confirm and further extend current knowledge with regards to the clinical usefulness of both antibodies in the context of acute demyelinating diseases. The authors studied a large cohort of 371 children from three large pediatric neurology centers in the UK with a suspected ADS. After clinical characterization, 237 children were diagnosed with an ADS and were further subdivided into different subsets such as ON, transverse myelitis, clinically isolated syndrome, or ADEM. The authors confirm that MOG antibodies are present in more than one-third of children with an ADS other than multiple sclerosis and are much more frequent than AQP4 antibodies. In addition, they show that MOG antibodies are highly specific for ADS other than multiple sclerosis and are not found in other neurological diseases affecting peripheral or central white matter. They further showed that not a single child with a clinical isolated syndrome who eventually developed multiple sclerosis harbored MOG antibodies, underscoring the utility of MOG and AQP4 antibodies in differentiating the diverse disease entities. Another interesting clinical detail reported in their study is that most children who presented with transverse myelitis regardless of other features (e.g. oligoclonal bands, multiple sclerosis-like magnetic resonance imaging) have a monophasic disease course and only rarely harbor MOG antibodies. Children with a further episode of transverse myelitis had either multiple sclerosis or a AQP4-positive NMOSD. Also of note was the finding that 50% of children who presented with an MOG-associated disease had further relapses. Secondly, children with a single event had declining MOG antibodies over time less often than previously reported, which is thought to be associated with a monophasic course. In addition, there was the observation of several investigators that patients who had a monophasic episode with subsequent decline and undetectable MOG antibody levels can have a second episode a decade later; this suggests that MOG antibody-mediated diseases might less often be self-limiting diseases. Other important issues such as the long-term outcome of children with recurrent MOG antibody-associated events, the predictive value of persisting serum MOG antibody levels in children in the context of a monophasic event, and the optimal treatment option of children with recurrent events remain so far unanswered. In a recent European collaborative study, Hacohen et al. showed that first-line disease modifying therapies used in pediatric multiple sclerosis are not beneficial in MOG-associated disease and require other treatment modalities such as intravenous immunoglobulins. Further studies are needed to answer the remaining open questions. As the authors suggest, MOG antibody-positive children should be closely followed with regular measurements of MOG antibody levels with live cell-based assays.