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Mitochondrial Dysfunction and Epilepsies
Published in Shamim I. Ahmad, Handbook of Mitochondrial Dysfunction, 2019
Bindu Parayil Sankaran, Arun B. Taly
MT-TK is a hot spot for mutation causing mitochondrial epilepsy. Mutations in MT-TK results in the classical mitochondrial syndrome- Myoclonic epilepsy with ragged red fibre syndrome denoted by the acronym- MERRF. The most common mutation in MERRF is the 8344A>G substitution in the gene encoding mt tRNA Lys present in more than 90% of the patients reported . (DiMauro and Hirano 1993) The other mutations reported are m.8356T>C, and m. 8363G>A mutations. (Silvestri et al. 1992) The canonical features of MERRF syndrome include myoclonus, generalized epilepsy, ataxia and ragged red fibres [RRF] or identification of a pathogenic variant. (DiMauro and Hirano 1993) MERRF is a multisystemic disorder. Besides epilepsy, other systemic manifestations are common which include hearing loss, peripheral neuropathy, cognitive decay and eventually dementia, short stature, exercise intolerance, optic atrophy among others. (Altmann et al. 2016; Mancuso et al. 2013) Less common clinical signs (seen in <50% of the patients) include cardiomyopathy, pigmentary retinopathy, pyramidal signs, ophthalmoparesis, and the appearance of multiple lipomas, particularly in the neck and upper trunk. (Lamperti and Zeviani 2016).
Mitochondrial DNA Mutations and Mitochondrial Diseases
Published in Sara C. Zapico, Mechanisms Linking Aging, Diseases and Biological Age Estimation, 2017
MERRF syndrome is a progressive, neurodegenerative disease which often presents in childhood or early adulthood following normal development. MERRF syndrome is characterized by myoclonic epilepsy, cerebellar ataxia and myopathy. In some cases it can be accompanied by dementia, deafness, optic atrophy, peripheral neuropathy, retinopathy and ophthalmoparesis. It is caused most commonly by a point mutation in the MT-TK gene, 8344A > G. Other mutations, such as 8356 T > C and 8363G > A are associated with this syndrome. The 8344A > G mutation always occurs in heteroplasmy and requires 95% of the mutated genomes to manifest the pathology. This mutation is also associated with other clinical phenotypes such as Leigh syndrome, myopathy, CPEO and MSL (Shoffner et al. 1990, Yoneda et al. 1990, Silvestri et al. 1993).
Neurogenetics
Published in John W. Scadding, Nicholas A. Losseff, Clinical Neurology, 2011
Sonia Gandhi, Sarah Tabrizi, Nicholas Wood
MERRF syndrome (myoclonic epilepsy with ragged red fibres) is caused in 90 per cent of cases by mutation 8344 in tRNA gene for lysine in the mitochondrial genome. This results in myoclonic and generalized seizures, myopathy, ataxia and dementia.
Pharmacotherapeutic management of epilepsy in MERRF syndrome
Published in Expert Opinion on Pharmacotherapy, 2019
It is now well defined how to diagnose MERRF syndrome [6]. There is increasing evidence that MERRF syndrome, as most MIDs, is a multisystem disorder affecting all tissues and not only the brain and the muscle. It is now also well appreciated that MERRF syndrome is not only associated with myoclonic seizures but also with a number of other seizure types. We also know that myocloni in MERRF may not only be due to epileptic activity but also due to cerebellar or spinal cord affection. Today, MERRF is considered rather as myoclonic ataxia than as myoclonic epilepsy.