Genetic testing and the phenotype of Polish patients with Unverricht–Lundborg disease (EPM1) — A cohort study

The aim of this study was to explore genetic findings and the phenotype in Polish patients with Unverricht–Lundborg disease (ULD). We retrospectively evaluated mutations in the cystatin B (CSTB) gene and clinical presentation in a cohort of patients with ULD. The study population consisted of 19 (14 males) patients with genetically confirmed disease. Sixteen patients were homozygous for the expanded dodecamer repeat mutation alleles, one subject was compound heterozygous for the dodecamer repeat expansion and other mutation, in two, the type of mutation has not yet been established. The numbers of repeats in the CSTB gene varied from 60 to 81. Clinical information was available for 16 subjects. The disease course was progressive in all patients, leading to severe disability, mainly due to myoclonus, in nine. Genetic findings and the clinical picture of our patients with ULD were in accordance with available studies. The most common genetic defect underlying ULD was homozygosity for an unstable expansion of a dodecamer repeat in the CSTB gene. Patients with action or/and stimulus sensitive myoclonus or intractable myoclonus epilepsy, especially with onset in late childhood/adolescence should be screened for ULD. •Genetic diagnosis is still delayed in patients with EPM1.•A homozygous expansion of dodecamer repeat in the CSTB gene accounts for most cases.•Patients with action/stimulus sensitive and/or intractable myoclonus should be analyzed for EPM1.