PRRT2 mutation causes benign familial infantile convulsions

Benign familial infantile convulsions (BFIC) is an autosomal dominantly inherited epilepsy syndrome with onset between 3 and 12 months of age. It is characterized by brief seizures with motor arrest, cyanosis, hypertonia, and limb jerks. Seizures respond well to antiepileptic drugs and remission occurs before the age of 3 years.¹ Several recent publications described heterozygous mutations in the proline-rich transmembrane protein 2 (PRRT2) gene on chromosome 16p11.2, one of the known BFIC loci,^2,3 in an increasingly large number of families with paroxysmal kinesigenic dyskinesia (PKD) and PKD with infantile convulsions (PKD/IC).^4-6 The majority of PRRT2 mutations result in a premature truncation of PRRT2 protein. Although its exact function is unknown, recent studies indicated that PRRT2 is highly expressed in the developing nervous system and localized in axons in primary neuronal cultures.⁶ Through binding to synaptic protein SNAP25, PRRT2 may be involved in vesicle docking and calcium-triggered neuronal exocytosis.⁶ Preliminary functional studies of truncated PRRT2 mutants showed either a loss of membrane localization in COS-7 cells⁵ or near absence of mutant protein in hippocampal neuronal cultures⁶ that is likely due to nonsense mediated RNA decay. One can speculate that mutant PRRT2 protein may result in abnormal neurotransmitter release and neuronal hyperexcitability that could explain the clinical symptoms seen with PKD and PKD/IC. We tested whether PRRT2 is also the causal gene in families with BFIC without associated paroxysmal dyskinesia.