Mutations in the potassium channel gene KCNQ2, usually cause benign familial neonatal epilepsy. This is an autosomal dominant disorder characterized by clusters of seizures occurring in the first days of life. Most patients have normal psychomotor development and spontaneous remission of seizures by 12 months of age. Since Rett and Teubel reported the first family in 1964 and the identification of KCNQ2 gene mutations in this family by Zimprich et al. in 2006, phenotypic variability has been recognized including: later onset of seizures, myokymia in isolation or accompanied by seizures, neurological deficit and mental retardation. We report a mother and son with an atypical presentation of familial neonatal epilepsy. The mother has persistent epilepsy and subnormal intelligence. The son developed a severe dyskinesia clinically compatible with multifocal myoclonus in the neonatal period that only responded to carbamazepine. He also has ataxia and delayed psychomotor development. EMG revealed a spontaneous occurrence of repetitive normal motor potentials in different muscle groups. Genetic analysis identified a heterozygous missense mutation in KCNQ2 in the child and his mother.

CONCLUSIONS

KCNQ2 mutations can present with a neonatal onset multifocal myoclonus-like dyskinesia.