Juvenile myoclonic epilepsy phenotype in a family with Unverricht-Lundborg disease

Unverricht-Lundborg disease (ULD), an autosomal recessive progressive myoclonus epilepsy, is due to an expansion, or less commonly a mutation, of the cystatin B (CSTB) gene. We report a clinical and molecular study of a Tunisian ULD family with five affected members presenting with a juvenile myoclonic epilepsy (JME)-like phenotype. The expansion of dodecamers was detected by a deamination/PCR assay. The expression profiles of CSTB and other candidate modifying genes, cathepsin B and cystatin C, were established by quantitative RT-PCR, and their respective transcription levels were compared with those from patients with a classic picture of ULD. Three patients had a fixed phenotype mimicking JME after 29 years of evolution. Only a discrete dysarthria was noticed in the two other patients. No correlation was observed between transcription level and severity of disease. Genetic screening should be performed in patients with a JME-like phenotype, when careful examination reveals discrete atypical signs of JME. This particular phenotype may be due to modifying genes and/or gene-environment interactions which require further clarification.