Approach to Progressive Myoclonic Epilepsies: Clinical Clues for Genetic Testing.

Progressive myoclonic epilepsy is a heterogeneous group of disorders characterized by drug-resistant epilepsy, cognitive decline, and ataxia. Genetic testing is crucial for diagnosis, but the choice of test depends on the variant type. We present a case of an adult with a PME phenotype since age 17 years, remaining undiagnosed for 4 years because of improper genetic testing. His father had progressive ataxia with a spinocerebellar ataxia phenotype. The unique presentation, combined with autosomal dominant inheritance and anticipation, suggested dentatorubral-pallidoluysian atrophy. ATN1 gene polymerase chain reaction testing confirmed trinucleotide repeat expansion. This case highlights the importance of selecting the appropriate genetic test for accurate diagnosis. We propose a flowchart based on clinical history and findings to narrow down differential diagnoses and guide the choice of testing.