Paroxysmal Kinesigenic Dyskinesia Caused by 16p11.2 Microdeletion: A Case Report.

Introduction: Paroxysmal kinesigenic dyskinesia (PKD) is a rare movement disorder which can present a diagnostic challenge. We present a case with video examples, of an uncommon cause of PKD. Case Presentation: A 16-year-old male presented with abrupt onset, brief episodes of right-sided head version, usually accompanied by extension of the left and rarely right arm. He experienced preceding bilateral sensory disturbance in his legs. His twin brother was diagnosed with focal seizures. There were no neurodevelopmental concerns. Sudden movement preceded stereotypical episodes. MRI brain was unremarkable. Home video and video EEG were utilised to reach a clinical diagnosis. The clinical phenotype of PKD was recognised, and he was treated with low-dose carbamazepine. Next-generation sequencing showed no pathogenic variant in gene panels for dystonia or channelopathies, including the common genes associated with PKD such as PRRT2 mutations. Subsequent microarray testing demonstrated a pathogenic 599 kb gene deletion on the 16p11.2 region, which includes the PRRT2 gene, confirming the diagnosis of PKD. Conclusion: PKD is an important diagnosis to consider due to the potential delay in diagnosis, genetic implications, and treatment responsiveness. Video recordings are valuable diagnostic tools. When suspecting PKD, screening for PRRT2 variants as well as 16p11.2 microdeletions should be considered.