Ataxia and Diplopia: A New -Related Phenotype.

Objectives: The objective of this study was to describe the first patient with recurrent ataxia and diplopia in association with a pathogenic variant in .

Methods: We identified a girl with a heterozygous pathogenic variant and performed thorough phenotyping.

Results: A 10-year-old girl was previously well with normal intelligence. She had recurrent diplopia, dysmetria, and unsteady gait, which occurred only in the context of febrile illnesses. EEG during her initial acute episode showed multifocal epileptiform discharges, with similar findings seen on a follow-up study 3 months later when she was well. Brain MRI finding was normal. A gene panel identified a de novo variant, p.Arg847Gln, classified as likely pathogenic. One year after her initial presentation, the girl is well and developmentally normal and has never had an event concerning for seizure.

Discussion: This case presentation demonstrates that pathogenic variants should be considered in children with transient ataxia, dysmetria, and diplopia in the context of viral febrile illnesses, even if there is no history of seizures. While there are clinical and molecular data suggesting that SCN8A dysfunction can cause temperature-sensitive phenotypes, further research is necessary to determine how the functional changes caused by our patient's variant result in her unique phenotype.