Changing Phenotype of Familial Paroxysmal Kinesigenic Dystonia when treated with Anti-epileptic Drugs Clare M Galtrey, Joseph Kaleyias, Antonia Clarke, Marie-Helene Marion Paroxysmal Kinesigenic Dystonia (PKD) typically presents with sudden, brief attacks of unilateral limb dystonia, triggered by sudden movement and responding to sodium channel inhibition. We report a teenager with typical familial PKD unilateral attacks starting at 8 years. After 5 years of successful treatment with oxcarbazepine she experienced recurrent attacks with a new phenotype; painful spasms involved limbs bilaterally and tongue occurred at rest lasting 90 min. They were triggered by TV, flashing lights and sudden noise with sirens passing her bedroom window resulting in attacks waking her from sleep. She had an uncomfortable feeling of tension and impending attacks all day without visible change. When the oxcarbazepine was withdrawn and replaced by phenobarbitone, the attacks reverted to a classical phenotype for 3 months and then the prolonged attacks re-emerged. We discuss how one patient developed several different phenotypes. Paroxysmal dyskinesias are associated with epilepsy. Recently the major PKD gene was identified as identified as proline-rich transmembrane protein 2 (PRRT2). Mutations in PRRT2 can cause PKD, benign familial infantile seizures and familial infantile convulsions with paroxysmal choreoathetosis so these diseases are part of a phenotypic spectrum. The function of PRRT2 is not known but it may indirectly affect channel function. There is overlap between PKD and other episodic diseases, such as epilepsy, migraine, and episodic ataxia that are channelopathies. The trigger for alteration of phenotype may be chronic drug treatment for example, treating childhood absence epilepsy with carbamazepine.