Many metabolic and genetic causes of progressive myoclonus epilepsy exist, and specific etiologies often present at certain ages. However, despite extensive evaluation, the cause of progressive myoclonus epilepsy may remain unknown in some patients. Causes that are recognized include:
Neurodegenerative conditions: Unverricht-Lundborg disease and Lafora disease.
Less commonly: Dentatorubo-pallidoluysian atrophy, juvenile Huntingtons, action-myoclonus-renal failure syndrome, juvenile neuroaxonal dystrophy, pantothenate-kinase associated neurodegeneration, neuroserpin inclusion body disease, leukoencephalopathy with vanishing white matter, early-onset Alzheimers and GOSR2 mutations.
Metabolic etiologies: mitochondrial disorders (MERRF), neuronal ceroid lipofuscinosis, sialidosis.
Less commonly: mitochondrial disorders (POLG1, MELAS, others), GM2 gangliosidoses, tetrahydrobiopterin deficiency, non-infantile neuronopathic Gaucher's disease and Niemann Pick type C.
This disease is the commonest cause of progressive myoclonus epilepsy, presenting with seizures before 18 years of age. Most cases originate from the Scandanavian or Baltic regions of Europe. Myoclonus gradually worsens and cognitive function slowly declines. The disorder has been linked to mutations in the Cystatin B (EMP1) gene. Phenytoin use aggravates the seizure disorder.
This disorder typically presents with seizures before 20 years of age and is rapidly progressive, with death in 10 years. The disorder has been linked to mutations in the EPM2A and EPM2B genes. Lafora bodies are found in cells in most organs (neurons, liver).