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Mitochondrial DNA point mutations are associated with various syndromes, among which mitochondrial myopathy, encephalopathy, lactic acidosis and stroke (MELAS) and myoclonic epilepsy with ragged red fibres (MERRF) are the most common.1 Here we present a case report of a young man with a mitochondrial encephalomyopathy caused by a mutation in the ND5 gene (13042A>G), which has been described previously.1
A 21-year-old man presented with a 2-year history of recurrent generalised epileptic seizures and myoclonus with no family history. Neurological examination revealed discrete nystagmus and multifocal myoclonus in the upper limbs, ataxia and focal dystonia presenting as writer's cramp. Neuropsychological examination showed slight working memory impairment and slowed learning of both verbal and visual material. Follow-up examinations conducted 18 and 33 months later did not show evidence of progression of the deficits. The patient exhibited anosodiaphoria throughout the observation period.
Laboratory studies showed a normal serum lactic acid level of 9.45 mg% with an abnormal lactic acid curve during ischaemic muscle exercise. Creatine kinase activity was within the normal range. A 50 min video EEG disclosed a pattern characteristic of myoclonic epilepsy. Visual evoked potentials showed delayed P100 responses. Electromyography and nerve conduction studies were within normal ranges. MRI showed hyperintensive lesions on T2 and FLAIR images in the right cerebral peduncle, close to the occipital horns of the lateral ventricles, in the left temporal lobe as well as …