Analysis of genetic characteristics in four children with atypical Rett syndrome and developmental epileptic encephalopathy caused by IQSEC2 gene variation

Abstract

Objective Summarize the clinical and genetic characteristics of atypical Rett syndrome and developmental epileptic encephalopathy caused by IQSEC2 gene variation. Methods and Results From May 2020 to April 2022, Anhui Provincial Children's Hospital diagnosed and treated 4 children with atypical Rett syndrome and developmental epileptic encephalopathy caused by IQSEC2 gene variation, including 2 males and 2 females were a pair of identical twins. They all had comprehensive developmental delay before onset. At the age of 2 years, all cases gradually exhibited clinical manifestations of atypical Rett syndrome, such as frequent clapping, biting, sleep disorders (increased sleep or difficulty falling asleep), and grinding teeth, followed by developmental regression and seizures. The initial age of epilepsy was from 2 years and 2 months to 2 years and 10 months. All cases started with generalized tonic-clonic seizure, with epileptic spasm occurring between 2 and 11 months of course. Case 2, Case 3 and Case 4 were also accompanied by focal seizures. Four cases with VEEG background of 4-6 Hz θ wave, the VEEG during the interictal phase was a broad multifocal sharp slow complex wave. In Case 2, Case 3 and Case 4,MRI was abnormal, mainly with increased depth of cerebral hemispheric sulcus and gyrus. The whole exome sequencing suggested pathogenicity and possible pathogenic variations in the IQSEC2 gene, Case 1 and Case 2 were frameshift mutations of c. 608dup (p. Gln204Profs*35), while Case 3 and Case 4 were nonsense mutations of c.2231C > A (p.Ser744Ter) and c.2521C > T (p.Gln841Ter), respectively. The four mutation sites have not been reported domestically or internationally. All cases received treatment with multiple antiepileptic seizure medicine. The last follow-up age was from 4 years and 3 months to 6 years and 3 months. All cases were unable to walk alone and had no active language. There were no seizures in Case 1 for 3 years, occasional seizures in Case 2 and Case 4, and frequent seizures in Case 3. Conclusions IQSEC2 gene variation can manifest as atypical Rett syndrome, which can be accompanied by refractory epileptic spasms. Both males and females have severe phenotypes, and the severity of clinical phenotypes at the same mutation site varies. Our report enriches the variation spectrum and clinical phenotype spectrum of the IQSEC2 gene, expands the genetic spectrum of Rett syndrome and developmental epileptic encephalopathy, and provides value for the clinical diagnosis, treatment and subsequent research of this disease.

Keywords

• rett syndrome
• epilepsy
• genes
• mutation