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Mitochondrial encephalomyopathy with lactic acidosis and stroke-like episodes (MELAS) and myoclonic epilepsy with ragged red fibres (MERRF) are phenotypes that have mainly been associated with mitochondrial tRNA gene point mutations. Clinical and genetic heterogeneity is also recognised and sometimes features of MERRF and MELAS can be found during the clinical course of some patients.1 These overlapped phenotypes have been related to other mtDNA point mutations (www.mitomap.org).
Here we report a patient with an overlapped MELAS/MERRF phenotype presenting the m.5521G>A mutation, located in the tRNATrp gene. Biochemical and molecular genetic analysis characterise this transition as a definitively pathological mutation.
Patient and methods
A woman developed sensorineural hearing loss at the age of 24 years. At the age of 36 years, she was studied for morning seizures with myoclonic movements in all four limbs. She also suffered from daily headaches and memory loss. Electroencephalography showed irregular point wave complex with a diffuse distribution. A brain CT demonstrated moderate cerebellar atrophy. Evoked auditive potentials had normal latency times and amplitudes below the normal range bilaterally. Psychiatric evaluation showed depressive syndrome. Histomorphological studies in a muscle biopsy revealed the presence of ragged red fibres and a diagnosis of MERRF syndrome was made. In the following years the patient suffered different types of seizures without drug control, persistent headache and weakness in the limbs, as well as cerebellar ataxia and cognitive deterioration. …
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