Pyridoxine-responsive KCNQ2 epileptic encephalopathy: Additional cases and literature review.

Background: Typical patients with KCNQ2 (OMIM# 602235) epileptic encephalopathy present early neonatal-onset intractable seizures with a burst suppression EEG pattern and severe developmental delay or regression, and those patients always fail first-line treatment with sodium channel blockers. Vitamin B6, either pyridoxine or pyridoxal 50-phosphate, has been demonstrated to improve seizure control in intractable epilepsy.

Methods: Here, we collected and summarized the clinical data for four independent cases diagnosed with pyridoxine-responsive epileptic encephalopathy, and their exome sequencing data. Moreover, we reviewed all published cases and summarized the clinical features, genetic variants, and treatment of pyridoxine-responsive KCNQ2 epileptic encephalopathy.

Results: All four cases showed refractory seizures during the neonatal period or infancy, accompanied by global development delay. Four pathogenetic variants of KCNQ2 were uncovered and confirmed by Sanger sequencing: KCNQ2 [NM_172107.4: c.2312C > T (p.Thr771Ile), c.873G > C (p.Arg291Ser), c.652 T > A (p.Trp218Arg) and c.913-915del (p. Phe305del)]. Sodium channel blockers and other anti-seizure medications failed to control their seizures. The frequency of seizures gradually decreased after treatment with high-dose pyridoxine. In case 1, case 2, and case 4, clinical seizures relapsed when pyridoxine was withdrawn, and seizures were controlled again when pyridoxine treatment was resumed.

Conclusion: Our study suggests that pyridoxine may be a promising adjunctive treatment option for patients with KCNQ2 epileptic encephalopathy.