LAUSR

An 18-year-old boy presented with a 5-year history of brief episodes of involuntary, random, flinging movements of all 4 limbs and trunk lasting for 30 to 60 seconds. These episodes were precipitated by sudden movements, occurring multiple times per day, and were preceded by unpleasant sensations with preserved consciousness. He did not have any history of epilepsy. His father and elder brother had similar complaints. The clinical examination of the patient between the episodes was normal. The typical attack showed a choreoballistic movement with dystonic posturing involving all 4 limbs, trunk, neck, and face (Video S1). There was no difference in the triggers inducing mild and severe attacks. Based on the phenomenology of the abnormal movements, positive family history, and specific trigger factor, a clinical diagnosis of paroxysmal kinesigenic dyskinesia (PKD) was made. Magnetic resonance imaging of the brain and electroencephalography were normal. On whole-exome sequencing, a heterozygous single base pair insertion in exon 2 of the PRRT2 gene (chr16:g.29825015_29825016insC; depth: 23×) that results in a frameshift and premature truncation of the protein 8 amino acids downstream to codon 217 (p.Arg217ProfsTer8; ENST00000567659.1) was detected (Fig. 1). The observed variation has previously been reported in patients affected with PKD. He was started on carbamazepine tablets (200 mg 2 times daily), resulting in a significant reduction (1–2 per week) in the frequency of attacks at the 1-month follow-up. The doses of carbamazepine