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Epilepsy affects approximately 1% of the world's population. Genetic factors and acquired etiologies, as well as a range of environmental triggers, together contribute to epileptogenesis.Wehave identified a family with three daughters affected with progressive myoclonus epilepsy with ataxia. Clinical details of the onset and progression of the neurologic presentation, epileptic seizures, and the natural history of progression over a 10-year period are described. Using autozygosity genetic mapping, we identified a high likelihood homozygous region on chromosome 7p12.1-7q11.22. We subsequently applied whole-exome sequencing and employed a rare variant prioritization analysis within the homozygous region. We identified p.Tyr276Cys in the potassium channel tetramerization domain-containing seven gene, KCTD7, which is expressed predominantly in the brain. Mutations in this gene have been implicated previously in epileptic phenotypes due to disturbances in potassium channel conductance. Pathogenicity of the mutation was supported by bioinformatic predictive analyses and variant cosegregation within the family. Further biologic validation is necessary to fully characterize the pathogenic mechanisms that explain the phenotypic causes of epilepsy with ataxia in these patients.