Impact of KCNQ2 mutations in Bulgarian patients with electroclinical syndromes with onset in the first year of life

Mutations in KCNQ2 are associated with a range of electroclinical syndromes with dominant inheritance that are differentiated by the age at onset of the seizures and are associated with good prognosis. These are benign familial neonatal seizures (BFNS), benign familial neonatal-infantile seizures (BFNIS) and benign familial infantile seizures. Herein, we report the results of a systematic screening of KCNQ2 in 27 unrelated Bulgarian patients with compatible clinical diagnoses. Two pathogenic point mutations were identified: a novel splice-site c. 1526-2A > G variation causing BFNS and a missense c. 998G > A alteration in a patient with BFNIS, who subsequently developed benign epilepsy with centro-temporal spikes. Additionally, multiplex ligation-dependent probe amplification analysis and array comparative genomic hybridization assay detected a de novo deletion on 20q13.3 encompassing 0.41 Mb genomic region and covering 11 genes, including KCNQ2 and CHRNA4. This large-scale rearrangement was found in a patient with typical BFNS and no additional developmental abnormalities. Overall, KCNQ2 genetic defects were found in 11% of the patients in our cohort. These findings enrich the genetic epidemiology and mutation spectrum of KCNQ2 and allow adequate genetic counselling in the affected families.