Case Report: Clinical Features of a Chinese Boy With Epileptic Seizures and Intellectual Disabilities Who Carries a Truncated Variant.

The mental retardation-55 with seizures (MRD55) is a rare genetic disease characterized by developmental delay, intellectual disability, language delay and multiple types of epileptic seizures. It is caused by pathogenic variants of the gene, which encodes Nogo-B receptor (NgBR), a necessary subunit for the glycosylation reactions in mammals. To date, 25 disease-causing mutations of have been reported, which are responsible for various diseases, including dystonia, Parkinson's disease, developmental and epileptic encephalopathy as well as congenital disorder of glycosylation. In addition, only 9 of these mutations were reported with detailed clinical features. There are no reports about Chinese cases with MRD55. In this study, a novel, pathogenic variant of (c.51_54delTCTG, p.L18Tfs31) was identified in a Chinese patient with intellectual disability and epileptic seizures. This pathogenic variant resulted in truncated NgBR proteins, which might be the cause of the clinical features of the patient. Oxcarbazepine was an effective treatment for improving speech and movement of the patient, who consequently presented with no seizure. With this novel pathogenic variant found in , we expand the genotype spectrum of MRD55 and provide valuable insights into the potential genotype-phenotype correlation.