Neonatal-Onset Opsoclonus-Myoclonus-Ataxia-Like Syndrome Caused by De Novo FRMD5 Variant Responsive to IV Steroid...

The FRMD5-associated neurodevelopmental disorder is characterized by early-onset abnormal eye movements, seizures, ataxia, nonepileptic myoclonus, and developmental delay with only symptomatic treatment available. Opsoclonus-myoclonus-ataxia syndrome has similar features with well-established immunomodulatory treatment. We present a case of a patient with a de novo FRMD5 variant responsive to steroid pulse therapy and provide phenotypic-genotypic correlation based on our case and reported data.

Serial MRI of the brain, chest, abdomen, and pelvis; I-123 MIBG scintigraphy; long-term video-EEG; infectious disease screening; and trio-exome sequencing were performed, and urine levels of vanillylmandelic and homovanillic acids were measured. Ataxia and cerebellar symptoms were assessed using the SARA and Mitchell-Pike OMS scales. A PubMed and SCOPUS search for FRMD5-related disorders was conducted until July 2024.

The de novo pathogenic variant in the FRMD5 gene (c.1051A>C, p.Ser351Arg) was identified. Pulsed IV methylprednisolone resulted in significant clinical improvement. The review of all existing cases, including ours, revealed clear genotype-phenotype correlation.

Our findings point to a possible causal relationship between the FRMD5 gene alteration and a subset of opsoclonus-myoclonus-ataxia syndrome, emphasizing the importance of genetic testing for this disease, especially with infantile onset and no identifiable cause. The significant improvement observed in our patient warrants further studies on steroids for FRMD5-related disorders.