Progressive myoclonic epilepsy
Progressive myoclonic epilepsy
Description, Causes and Risk Factors:
Progressive myoclonus epilepsies are a heterogeneous group of inherited disorders defined by the association of myoclonus, epilepsy and progressive neurological deterioration.
Progressive myoclonus epilepsy is a group of conditions involving the CNS (central nervous system) and representing more than a dozen different diseases. These diseases share certain features, including a worsening of symptoms over time and the presence of both muscle contractions (myoclonus) and seizures (epilepsy). Patients may have more than one type of seizure, such as petit mal or grand mal. PME is progressive, but the rate of progression may be quick or slow, depending on the underlying disease.
Progressive myoclonus epilepsy is different from myoclonic epilepsy. In myoclonic epilepsy, the myoclonic jerking motions occur as part of the seizure. In PME, myoclonus occurs separately from seizures, the two respond differently to the same drugs, they evolve differently during the natural history of the disease, and they cause different problems for the patient.
Hereditary metabolic disorders are often responsible, but sometimes metabolic test results are normal and the cause remains unknown. The disorders affect both sexes. The age of onset can vary from infancy to adulthood, depending upon the specific type of myoclonic epilepsy.
PME accounts for less than 1% of epilepsy cases at Specialist Centres. The incidence and prevalence of PME is unknown, but there are considerable geography and ethnic variations amongst the specific genetic disorders. The disease is more common in European-American descent.
Recent advances in molecular genetics have significantly increased the understanding of the basic mechanisms involved in the PMEs. Positional cloning has been used successfully to identify genes underlying the major forms of PME. In addition, several genes for the more rare forms have been identified, e.g. the DRPLA gene underlying Dentatorubral-pallidoluysian atrophy found predominantly in Japan. The research now aims at understanding the function of the proteins encoded by the PME genes as well as revealing the underlying disturbed metabolic pathways.
Progressive myoclonic epilepsies feature a combination of myoclonic and tonic-clonic seizures. Unsteadiness, muscle rigidity, and mental deterioration are often present. The onset of symptoms varies generally from childhood to adolescence but can be in the adulthood.The disease progression is slow, with in-coordination and dysarthria developing over time.
Progressive myoclonus epilepsy is diagnosed by clinical findings and electroencephalogram (EEG) results. Molecular genetic testing is available for some of the genes associated with other types of PME.
The analytical sensitivity of the sequencing test is estimated to be 98%. It will not reliably detect deletions, insertions, or rearrangements greater than or equal to ten base pairs.
Clinical sensitivity of sequencing and deletions/duplications analysis of the 12 genes included in the progressive myoclonic epilepsy panel depends in part on the patient's clinical phenotype.
The deletions/duplications testing can detect deletions and/or duplications encompassing one or more exons, including mutations as small as 150 to 300 base pairs.
The presence of any potentially disease-associated sequence variants or copy number mutations is confirmed by dideoxy DNA sequence analysis or quantitative PCR, respectively, or by other methods, as appropriate.
Treatment of progressive myoclonus epilepsy includes the anticonvulsant drugs clonazepam, divalproex, and primidone in much the same dosages used to treat epilepsy. In all cases, the better advice is to start with low doses and work upwards. The diets of patients taking divalproex chronically should be supplemented with carnitine.
Low dose oral contraceptives may be of help to women who experience heightened myoclonus or seizures during menstruation.
Genetic counseling is recommended for affected individuals and their families. Other treatment is symptomatic and supportive.
NOTE: The above information is for processing purpose. The information provided herein should not be used during any medical emergency or for the diagnosis or treatment of any medical condition.
DISCLAIMER: This information should not substitute for seeking responsible, professional medical care.
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