COMPARATIVE STUDY
JOURNAL ARTICLE

KCNQ2 encephalopathy: emerging phenotype of a neonatal epileptic encephalopathy

Sarah Weckhuysen, Simone Mandelstam, Arvid Suls, Dominique Audenaert, Tine Deconinck, Lieve R F Claes, Liesbet Deprez, Katrien Smets, Dimitrina Hristova, Iglika Yordanova, Albena Jordanova, Berten Ceulemans, An Jansen, Danièle Hasaerts, Filip Roelens, Lieven Lagae, Simone Yendle, Thorsten Stanley, Sarah E Heron, John C Mulley, Samuel F Berkovic, Ingrid E Scheffer, Peter de Jonghe
Annals of Neurology 2012, 71 (1): 15-25
22275249

OBJECTIVE: KCNQ2 and KCNQ3 mutations are known to be responsible for benign familial neonatal seizures (BFNS). A few reports on patients with a KCNQ2 mutation with a more severe outcome exist, but a definite relationship has not been established. In this study we investigated whether KCNQ2/3 mutations are a frequent cause of epileptic encephalopathies with an early onset and whether a recognizable phenotype exists.

METHODS: We analyzed 80 patients with unexplained neonatal or early-infantile seizures and associated psychomotor retardation for KCNQ2 and KCNQ3 mutations. Clinical and imaging data were reviewed in detail.

RESULTS: We found 7 different heterozygous KCNQ2 mutations in 8 patients (8/80; 10%); 6 mutations arose de novo. One parent with a milder phenotype was mosaic for the mutation. No KCNQ3 mutations were found. The 8 patients had onset of intractable seizures in the first week of life with a prominent tonic component. Seizures generally resolved by age 3 years but the children had profound, or less frequently severe, intellectual disability with motor impairment. Electroencephalography (EEG) at onset showed a burst-suppression pattern or multifocal epileptiform activity. Early magnetic resonance imaging (MRI) of the brain showed characteristic hyperintensities in the basal ganglia and thalamus that later resolved.

INTERPRETATION: KCNQ2 mutations are found in a substantial proportion of patients with a neonatal epileptic encephalopathy with a potentially recognizable electroclinical and radiological phenotype. This suggests that KCNQ2 screening should be included in the diagnostic workup of refractory neonatal seizures of unknown origin.

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