Early-Onset Epilepsy in Infancy Associated with Mutations in KCNQ2 and SCN8A: A Report of Two Cases

Neonatal seizures are most commonly attributed to hypoxic-ischaemic injury, metabolic abnormalities, or central nervous system infections; however, an increasing proportion of cases are recognised to have an underlying genetic aetiology, particularly when routine investigations are non-contributory. Present report is of two neonates with early-onset seizures caused by distinct monogenic channelopathies who demonstrated markedly divergent clinical courses and outcomes. The first case was a near-term female neonate who presented on day 8 of life with recurrent tonic seizures and a significant family history of unexplained infantile death in a sibling. Comprehensive evaluation revealed no metabolic or structural abnormalities. Whole-Exome Sequencing (WES) identified a heterozygous pathogenic loss-of-function variant in the KCNQ2 gene. Seizures were controlled with phenobarbital monotherapy, and the infant remained seizure-free with age-appropriate neurodevelopment at 12 months of follow-up. The second case was a term male neonate who presented on day 11 of life with focal autonomic seizure clusters. Magnetic Resonance Imaging (MRI) brain demonstrated non-specific pachymeningeal enhancement. Despite treatment with five antiepileptic drugs (AEDs), seizures remained pharmacoresistant. Genetic analysis revealed a heterozygous variant of uncertain significance (VUS) in the SCN8A gene (c.1157C>A; p.Thr386Lys) and an additional heterozygous SLC6A1 variant (c.582G>T; p.Glu194Asp). By four months of age, the infant exhibited profound global developmental delay. These cases illustrate contrasting clinical trajectories in neonatal channelopathies with similar ages at seizure onset.