Novel KCNQ2 Variants Related to a Variable Phenotypic Spectrum Ranging from Epilepsy with Auditory Features to Severe Developmental and Epileptic Encephalopathies

Pathogenic KCNQ2 variants are associated with neonatal epilepsies, ranging from self-limited neonatal epilepsy to KCNQ2-developmental and epileptic encephalopathy (DEE). In this study, next-generation sequencing was performed, applying a panel of 142 epilepsy genes on three unrelated individuals and affected family members, showing a wide variability in the epileptic spectrum. The genetic analysis revealed two likely pathogenic missense variants (c.1378G>A and c.2251T>G) and the already-reported pathogenic splice site (c.1631+1G>A) in KCNQ2 (HGNC:6296). The phenotypes observed in the affected members of family 1, which shared the c.2251T>G variant, were epilepsy with auditory features (EAFs), focal epilepsy, and generalized epilepsy, and none of them suffered from neonatal seizures. The gene panel contained further genes related to EAFs (LGI1, RELN, SCN1A, and DEPDC5), which were tested with negative results. The phenotypes observed in family 2 members, sharing the splice site variant, were neonatal seizures and focal epilepsy in childhood. The last unrelated proband, harboring the de novo missense c.1378G>A, presented a clinical phenotype consistent with DEE. In conclusion, we identified two unreported KCNQ2 variants, and report a proband with EAFs and individuals without typical KCNQ2 neonatal seizures. Our study underscores the extreme variability in the phenotypic spectrum of KCNQ2-related epilepsies and unveils the prospect of its inclusion in screening panels for EAFs.