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Epilepsies, Myoclonic definition: A clinically diverse group of epilepsy syndromes characterized either by myoclonic seizures or by myoclonus in association with other seizure types. Myoclonic epilepsy syndromes are divided into three subtypes based on etiology: familial, cryptogenic, and symptomatic (i.e., occurring secondary to known disease processes such as infections, hypoxic-ischemic injuries, trauma, etc.).
myoclonus epilepsy definition: any form of epilepsy accompanied by myoclonus, shock like contractions of the muscle.
MERRF Syndrome definition: A mitochondrial encephalomyopathy characterized clinically by a mixed seizure disorder, myoclonus, progressive ataxia, spasticity, and a mild myopathy. Dysarthria, optic atrophy, growth retardation, deafness, and dementia may also occur. This condition tends to present in childhood and to be transmitted via maternal lineage. Muscle biopsies reveal ragged-red fibers and respiratory chain enzymatic defects. (From Adams et al., Principles of Neurology, 6th ed, p986)
Myoclonic Epilepsy, Juvenile definition: A disorder characterized by the onset of myoclonus in adolescence, a marked increase in the incidence of absence seizures (see EPILEPSY, ABSENCE), and generalized major motor seizures (see EPILEPSY, TONIC-CLONIC). The myoclonic episodes tend to occur shortly after awakening. Seizures tend to be aggravated by sleep deprivation and alcohol consumption. Hereditary and sporadic forms have been identified. (From Adams et al., Principles of Neurology, 6th ed, p323)
Myoclonic Epilepsies, Progressive definition: A heterogeneous group of primarily familial disorders characterized by myoclonic seizures, tonic-clonic seizures, ataxia, progressive intellectual deterioration, and neuronal degeneration. These include LAFORA DISEASE; MERRF SYNDROME; NEURONAL CEROID-LIPOFUSCINOSIS; sialidosis (see MUCOLIPIDOSES), and UNVERRICHT-LUNDBORG SYNDROME.
Lafora Disease definition: A form of stimulus sensitive myoclonic epilepsy inherited as an autosomal recessive condition. The most common presenting feature is a single seizure in the second decade of life. This is followed by progressive myoclonus, myoclonic seizures, tonic-clonic seizures, focal occipital seizures, intellectual decline, and severe motor and coordination impairments. Most affected individuals do not live past the age of 25 years. Concentric amyloid (Lafora) bodies are found in neurons, liver, skin, bone, and muscle (From Menkes, Textbook of Childhood Neurology, 5th ed, pp111-110)
Unverricht-Lundborg Syndrome definition: An autosomal recessive condition characterized by recurrent myoclonic and generalized seizures, ATAXIA, slowly progressive intellectual deterioration, dysarthria, and intention tremor. Myoclonic seizures are severe and continuous, and tend to be triggered by movement, stress, and sensory stimuli. The age of onset is between 8 and 13 years, and the condition is relatively frequent in the Baltic region, especially Finland. (From Menkes, Textbook of Child Neurology, 5th ed, pp109-110)
 
Examples
 

The wild-type tRNALysand the corresponding tRNALyscarrying the A8344G mutation associated with the MERRF (Myoclonic Epilepsy with Ragged Red Fibers) syndrome exhibit the same modified nucleotides at the same molar concentrations.

M Helm et al.

Nucleic Acids Research 27 (3), 01 Feb 1999

Using this technique, the levels of three point mutations, the tRNA Leu(UUA) 3243 mutation causing mitochondrial encephalopathy, lactic acidosis and stroke-like episodes (MELAS); the tRNA Lys 8344 mutation causing myoclonic epilepsy and ragged red fibers (MERRF); and the nucleotide position 414 mutation adjacent to the control region promoters, were evaluated in human brain and muscle from individuals of various ages.

D. G. Murdock et al.

Nucleic Acids Research 28 (21), 01 Nov 2000

Several studies have reported that the pathogenic mtDNA tRNA Leu(UUA) A3243G mutation causing mitochondrial encephalopathy, lactic acidosis and stroke-like episodes (MELAS) and the mtDNA tRNA Lys A8344G mutation causing myoclonic epilepsy and ragged red fibers (MERRF) disease, accumulates with age in various tissues in healthy individuals ( 15 – 18 ).

D. G. Murdock et al.

Nucleic Acids Research 28 (21), 01 Nov 2000

Brd2 facilitates expression of genes promoting proliferation and is implicated in apoptosis and in egg maturation and meiotic competence in mammals; it is also a susceptibility gene for juvenile myoclonic epilepsy (JME) in humans.

Angela J DiBenedetto et al.

BMC Developmental Biology 8 (7), 10 Apr 2008

Consistent with a role in neuronal development, human Brd2 has recently been identified as the major susceptibility gene for juvenile myoclonic epilepsy [ 26 ].

Angela J DiBenedetto et al.

BMC Developmental Biology 8 (7), 10 Apr 2008

 
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