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Cortical reflex myoclonus in patients with the mitochondrial DNA transfer RNA(Lys)(8344) (MERRF) mutation
P D Thompson1, S R Hammans, A E Harding
1Human Movement and Balance Unit, Institute of Neurology, London, UK.
Abstract:
Five patients from three families with the syndrome of myoclonic epilepsy and ragged red fibres (MERRF), associated with the mitochondrial DNA point mutation at position 8344, were studied neurophysiologically to determine the characteristics of their myoclonus. The findings were those of cortical reflex myoclonus, with enlarged cortical somatosensory evoked potentials and late reflex responses to peripheral nerve stimulation. Electroencephalography showed paroxysmal spike and polyspike and wave discharges, with photic sensitivity. This pattern of electrophysiological abnormalities was uniform, despite considerable variation in severity of myoclonus. Although a consistent finding, cortical reflex myoclonus is not specific to MERRF amongst myoclonic syndromes.
Insights
Neurophysiological studies revealed cortical reflex myoclonus in patients with myoclonic epilepsy and ragged red fibers (MERRF) syndrome. This pattern, characterized by specific electrophysiological abnormalities, was consistent across patients with this mitochondrial DNA mutation.
Area of Science:
- Neurophysiology
- Mitochondrial Genetics
- Epilepsy Syndromes
Background:
- Myoclonic epilepsy and ragged red fibers (MERRF) is a mitochondrial disorder.
- A specific mitochondrial DNA point mutation at position 8344 is associated with MERRF.
- The neurophysiological characteristics of myoclonus in MERRF require detailed investigation.
Purpose of the Study:
- To neurophysiologically characterize the myoclonus in patients with MERRF syndrome.
- To investigate the electrophysiological abnormalities associated with the mitochondrial DNA 8344 point mutation.
- To determine if the observed neurophysiological pattern is specific to MERRF.
Main Methods:
- Neurophysiological assessment of five patients from three families with MERRF.
- Evaluation included electroencephalography (EEG) and evoked potential studies (somatosensory evoked potentials, late reflex responses).
- Analysis of electrophysiological findings in relation to clinical presentation and mitochondrial DNA mutation.
Main Results:
- Patients exhibited cortical reflex myoclonus.
- Enlarged cortical somatosensory evoked potentials and late reflex responses were observed.
- EEG revealed paroxysmal discharges and photic sensitivity, a uniform pattern despite variable clinical severity.
Conclusions:
- Cortical reflex myoclonus is a consistent neurophysiological finding in MERRF patients with the 8344 mitochondrial DNA mutation.
- The observed electrophysiological pattern is uniform, suggesting a common underlying mechanism.
- While characteristic, cortical reflex myoclonus is not exclusive to MERRF among myoclonic syndromes.