A Case of Paroxysmal Exercise-Induced Dyskinesia Expands the Phenotypic spectrum of <i>NAXE</i> -Related Encephalopathy

Progressive encephalopathy with brain edema and/or leukoencephalopathy-1 (PEBEL1) is a rare neurodegenerative disorder caused by pathogenic variants in NAXE gene. Movement disorders are among the clinical features of PEBEL1; however, no case presenting with paroxysmal exercise-induced dyskinesia (PED) has been reported. We reported the case of a 14-year-old girl who presented with PED episodes. Six months after the onset of episodes, she developed encephalopathy and focal status epilepticus. Exome sequencing analysis identified a homozygous pathogenic variant in NAXE gene, and she was diagnosed with PEBEL1. She was started on mitochondrial cocktail and multiple antiseizure medications; however, no response was observed. With the ketogenic diet (KD), seizure control was achieved and improvement in cognitive functions was observed. PED is a clinical feature not previously reported in PEBEL1 cases, and our case expands the phenotypic spectrum of this disorder. Additionally, our case highlights that KD may be a treatment option in PEBEL1.