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Título

Phenotypic variability in two siblings with Unverricht-Lundborg disease: juvenile myoclonic epilepsy phenotype x classic phenotype

RESUMO

Case presentation: Here, we present two siblings with consanguineous parents (first-degree cousins) and an uncle with a history of epilepsy. Case 1: A 28-year-old female with a history of myoclonic epilepsy since she was 10-years-old that became worse over time. She had normal psychomotor development until 11-years-old. Physical examination demonstrated global ataxia, intense action myoclonus and psychotic symptoms. Genetic testing revealed homozygous variant for the dodecamer expansion in the cystatin B (CTSB) gene, which confirmed the clinical diagnosis of Unverricht-Lundborg Disease (ULD). She scored 21/30 in the Mini-mental state examination (MMSE) and 28 in the Scale for the Assessment and Rating of Ataxia (SARA). Brain MRI disclosed diffuse cerebral and cerebellar atrophy. Case 2: Brother of Case 1, 23-year-old, who developed tonic-clonic seizures and occasional myoclonus that started at 11-years-old. Psychomotor development was normal. On examination he didn’t exhibit action myoclonus. Coordination tests and gait were preserved. He scored 30/30 in the MMSE and 29/30 in the Montreal Cognitive Assessment (MOCA). Electroencephalography showed sparse paroxysms of generalized spike-wave and polyspike-wave epileptiform activity, with normal baseline activity. Brain Magnetic Resonance Imaging was normal. Discussion: Unverricht-Lundborg Disease (ULD) is a rare, disabling and severe genetic condition associated with pathogenic variants in CSTB. ULD is considered the most common form of Progressive Myoclonus Epilepsy (PME). In our cases, the sister expressed a classic ULD phenotype while the brother presented a relatively mild phenotype, which can be mistaken for similar conditions as Juvenile Myoclonic Epilepsy (JME). The relative intensity of the various symptoms and the speed at which the disease progresses can vary, even within the same family. Therefore, it isn’t possible to assume that the brother’s disease will progress in a similar way to his sister’s condition. Final considerations: In this report we aimed to describe the first case of a JME-like phenotype and a classic ULD phenotype in siblings. This highlights the possibility of searching for ULD in some cases of families with clinical diagnosis of juvenile myoclonic epilepsy.