[Clinical features of KCNB1 gene variation related developmental and epileptic encephalopathy]

Objective: To summarize the clinical features of epilepsy and (or) developmental delay associated with KCNB1 gene variants in children. Methods: A case series study was conducted on 24 children with KCNB1 gene variants associated with epilepsy and (or) developmental delay who were treated at the Children's Medical Center of Peking University First Hospital and the Department of Neurology of Shenzhen Children's Hospital from July 2015 to June 2024. The manifestations of seizures, electroencephalogram (EEG) and genetic test results of those children were analyzed. Results: All the KCNB1 gene variants were de novo, involving 20 different variation, including 15 missense variations, 3 frameshift variations and 2 nonsense variations. There were 7 novel variations. Among the 24 developmental and epileptic encephalopathy children, there were 14 boys and 10 girls. The last follow-up age ranged from 9 months to 13 years and 9 months. Seizures were present in 21 children (88%), with onset ranging from 1 month to 7 years, and 76% (16/21) began before 2 years of age. The seizure types included focal seizures in 15 children (71%), epileptic spasms, myoclonic seizures, and generalized tonic-clonic seizures in 6 children respectively, atypical absence seizures in 4 children, and myoclonic atonic seizures in 1 child. Seventeen children (81%) had a cluster of seizures and 5 had a history of focal status epilepticus with impaired consciousness. All 24 children had varying degrees of developmental delay, with 3 presenting solely developmental delay. EEG abnormalities were present in all the 21 children with seizures, including focal or multifocal discharges in 20 children, generalized discharges in 10 children, hypsarrhythmia in 2 children, and electrical status epilepticus during sleep in 3 children. Magnetic resonance imaging abnormalities were found in 5 of the 24 children. Among the 21 children with seizures, 57% (12/21) achieved seizure control. Conclusions: KCNB1 gene variants are predominantly de novo missense variation. Most affected children present with epilepsy, though some may exhibit only developmental delay. Epilepsy often begins before 2 years of age, with focal seizures being the most common type. About 80% of patients experience clustered seizures. Although most patients achieve seizure control, they still exhibit varying degrees of developmental delay, consistent with developmental epileptic encephalopathy.