A patient with early myoclonic encephalopathy (EME) with a de novo KCNQ2 mutation

The potassium voltage-gated channel subfamily Q member 2 (KCNQ2) gene has been reported to be associated with various types of epilepsy, including benign familial neonatal seizure (BFNS), early infantile epileptic encephalopathy (EIEE), and unclassified early onset encephalopathies. We herein report a patient with early myoclonic encephalopathy (EME) caused by a KCNQ2 mutation.

A male infant started to exhibit erratic myoclonus several days after birth and apnea attacks lasting for seconds with desaturation. One month after birth, his myoclonuses worsened in frequency. Electroencephalogram (EEG) showed a burst and suppression pattern, and myoclonuses occurred in the burst phase with diffuse polyspikes on EEG. At five months, inter-ictal EEG revealed hypsarrhythmia, but his attacks were still only myoclonuses. ACTH treatment was effective and the myoclonus frequency markedly decreased. At one year of age, whole-exome sequencing revealed a heterozygous mutation of the KCNQ2 gene (NM_172107.2): c.601C>T; p.(Arg201Cys), which was confirmed as de novo by Sanger sequencing. This mutation lies within the extracellular portion of the S4 voltage sensor.

Most patients with a KCNQ2 mutation present with seizures starting in the neonatal period with varying severity, ranging from BFNS to Ohtahara syndrome. Furthermore, KCNQ2 appears to be a causative gene for EME.