To investigate the clinical phenotype and genetic characteristics of developmental epileptic encephalopathy 18 (DEE18) caused by SZT2 gene variants.

Clinical data of 2 children with SZT2 related DEE18 who visited the Department of Pediatric Neurology, Linyi People′s Hospital in March 2020 and July 2023 were collected. The whole exome sequencing (WES) and Sanger sequencing were applied to verify the child and their parents. SWISS-MODEL software was used to perform protein 3D modeling for the selected SZT2 gene variants.

Both of the 2 cases showed severe global developmental delay, epileptic seizures, autism, megacephaly, facial deformity, hypotonia, corpus callosum malformation, persistent cavum septum pellucidum, and slow background activity and focal discharge in video electroencephalography. Case 1 was easy to startle and thin in stature; case 2 had immune deficiency and clustered seizures. WES results showed that case 1 carried a compound heterozygous variant of c.5811G>A (p.W1937X) (paternal) and c.9269delG (p.S3090Ifs^*94) (maternal), while case 2 carried a compound heterozygous variant of c.6302A>C(p.H2101P) (paternal) and c.7584dupA (p.E2529Rfs^*20) (maternal), the parents of both patients with normal clinical phenotypes. The 4 mutations mentioned above were novel variations that had not yet been reported domestically or internationally. According to the American College of Medical Genetics and Genomics variant classification criteria and guidelines, the p.S3090Ifs^*94 variant was interpreted as pathogenic; p.W1937X variant was interpreted as pathogenic; p.E2529Rfs^*20 variant was interpreted as likely pathogenic; p.H2101P variant was interpreted as uncertain significance. 3D modeling showed that the variant of p.H2101P resulted in a significant change in the hydrogen bond around the 2 101st amino acid encoded, leading to a decrease in protein stability. The other 3 variants led to early truncation of peptide chain and obvious changes in protein structure.

DEE18 caused by SZT2 gene mutation is mainly an autosome recessive genetic disease, and its clinical manifestations include global developmental delay, epileptic seizures, autism, craniofacial malformation, hypotonia, epileptic discharge, corpus callosum malformation, persistent cavum septum pellucidum, shock, small and thin stature, and immune deficiency. Four novel variants related to the SZT2 gene may be the genetic etiology of DEE18 patients in this study.

Epilepsy; Developmental disabilities; SZT2 gene; Missense mutation; Congenital abnormalities; Whole exome sequencing