Abstracts

Rationale: Myoclonic epilepsy is a major symptom in patients with mitochondrial encephalopathy. Mutations were found in the mitochondrial DNA such as tRNALys in case of MERRF (myoclonic epilepsy with ragged red fibers) or in tRNALeu in MELAS (mitochondrial myopathy, encephalopathy, lactic acidosis, stroke-like epilepsodes). In both syndromes mutations were also found in tRNAPhe. Methods: Here we describe a 40 year old patient with prominent myoclonic seizures since one year and sequencing of the mitochondrial DNA from a skeletal muscle biopsy. Results: The myoclonia are observed at upper and lower extremities, sometimes rhythmic but independent from awakening time. Neurological examination was normal but a slight mental retardation was found in a neuropsychological testing. The patient suffered also from a progressive severe hearing loss based on a defect of the inner ear on both sides. Ictal electroencephalography (EEG) showed bilateral occipital and generalized spikes and polyspikes. The seizures and epileptic discharges could be elicited by photostimulation. The background EEG was normal. Seizures responded well to levetiracetam and the patient became seizure-free under 2000mg/d. A cranial magnetresonancetomograhy (cMRT) detected a global atrophy of the brain and mild periventricular white matter lesions. The electromyography found no pathological changes leading to a myopathy but the muscle biopsy showed abundant ragged red fibers. Sequencing of the mitochondrial DNA from the skeletal muscle biopsy revealed a novel heteroplasmic mutation (A4279G) in the mitochondrial tRNAIleu (MT-TI) gene. Conclusions: The identified mutation changes a highly conserved nucleotide in the D-loop of this particular tRNA, which is likely to alter the tertiary structure of the tRNA affecting translation of mitochondrially encoded proteins. Interestingly, the degree of heteroplasmy of this novel mitochondrial DNA mutation was 57% in skeletal muscle but only 10% in blood, pointing to the diagnostic importance of a skeletal muscle biopsy also in patients with myoclonic epilepsy.