Progressive myoclonus epilepsy
| Progressive myoclonus epilepsy[1] | |
|---|---|
| Specialty | Neurology |
Progressive myoclonus epilepsy (PME) is a rare epilepsy syndrome caused by a variety of genetic disorders.[2] The syndrome includes myoclonic seizures and tonic-clonic seizures together with progressive neurological decline.
Signs and symptoms[]
 | This section does not cite any sources. (April 2013) |
Myoclonic seizures involve brief involuntary muscle twitching, and may become frequent enough to be disabling. Tonic-clonic seizures have two phases: the tonic phase may last a few seconds and involves the muscles tensing, and may lead to the person falling down; the clonic phase involves a convulsion of rapidly alternating muscle tensing and relaxing. Neurological dysfunction includes difficulty coordinating muscle movements (ataxia) and a decline in cognitive ability (dementia).
Differential diagnosis[]
| This section does not cite any sources. (April 2013) |
In the early stages, it can be difficult to distinguish progressive myoclonic epilepsy from benign idiopathic generalised epilepsies, such as juvenile myoclonic epilepsy. With PME, the initial effectiveness of anticonvulsant treatment diminishes as seizures become more frequent and neurological decline progresses. However, these can also be signs of anticonvulsant intoxication. The myoclonus in PME is usually severe and is the prominent seizure type.
Specific disorders[]
Several conditions can cause progressive myoclonic epilepsy.
- Unverricht-Lundborg disease (Baltic myoclonus)
- Myoclonus epilepsy and ragged red fibres (MERRF syndrome)
- Lafora disease
- Neuronal ceroid lipofuscinoses
- Sialidosis
- Dentatorubropallidoluysian atrophy (DRPLA)
- Noninfantile neuronopathic form of Gaucher disease
- Tetrahydrobiopterin deficiencies
- Alpers disease
- Juvenile Huntington disease[3]
- Niemann-Pick disease type C
- (NSPME)
Unverricht-Lundborg disease[]
This disease manifests between six and sixteen years and is most prevalent in Scandinavia and the Baltic countries. Myoclonus gradually becomes worse and less susceptible to medication. Cognitive decline is slow and sometimes mild. Patients typically do not live beyond middle-age, but there are exceptions. Phenytoin, an old and commonly used anticonvulsant, is known to seriously exacerbate the condition. It has autosomal recessive inheritance, and is caused by a mutation in the cystatin B (EPM1) gene on chromosome 21q22.3, which was discovered in 1996.
It has been described as the least severe type of PME.[4]
Myoclonus epilepsy and ragged red fibres (MERRF syndrome)[]
Onset of this disease may be at any time and the severity and progression are varied. Tonic-clonic seizures and dementia are less apparent than with other forms of PME. The cause is a mitochondrial DNA mutation, so most familial cases are transmitted from the mother. A skeletal muscle biopsy will show ragged red fibres, hence the name.
Lafora body disease[]
This disease typically begins between six and nineteen years after apparently normal development and generally results in death within ten years. It is characterised by the presence of Lafora bodies (polyglucosan inclusions) in neurons and other body tissue. The generalized seizures are usually well controlled by anticonvulsants, but the myoclonus soon proves refractory to treatment. Within a couple of years, a wheelchair is required for locomotion and within five to ten years, the person is confined to bed and is often tube fed. Valproic acid and zonisamide are first choice anticonvulsants, and the ketogenic diet may be helpful. An autosomal-recessive genetic defect is responsible, which has been tracked down to two genes. The EPM2A gene on chromosome 6q24 was discovered in 1998 and encodes for the protein laforin. It is responsible for 80% of cases. The EPM2B gene on chromosome 6p22.3 was discovered in 2003 and encodes for the protein . There may be a third gene of unknown locus.
Neuronal ceroid lipofuscinoses[]
There are various forms of these disorders, each with their own genetic cause and geographical variation, which lead to accumulation of lipopigments (lipofuscin) in the body's tissues and are inherited in an autosomal-recessive fashion. Onset and symptoms vary with the particular form, but death usually occurs within five to fifteen years.
Type I sialidosis[]
This is an autosomal recessive disorder in which the body is deficient in α-neuraminidase.
Myoclonic epilepsy and ataxia due to potassium (K+) channel mutation (MEAK)[]
MEAK is a form of progressive myoclonus epilepsy that typically begins between the ages of 3 and 15 years (the average of onset is 10 years). The first symptoms may include ataxia and myoclonus (unsteadiness and difficulty coordinating movements), along with generalized tonic-clonic (“grand mal”) seizures. Individuals with MEAK typically do not experience developmental delays. The symptoms are progressive, and individuals with MEAK often need to use a wheelchair by their late teenage years because of movement difficulties and myoclonus. Many individuals with MEAK report temporary improvement of symptoms when they have a high fever. Seizures may become less frequent in adulthood, but other neurological complications, including myoclonus, ataxia and tremor, may worsen. Myoclonic epilepsy and ataxia due to potassium (K+) channel mutation (MEAK) is caused by a specific pathogenic variant (“mutation”) in KCNC1 (c.959G>A; p.Arg320His). KCNC1-related developmental and epileptic encephalopathy is associated with other pathogenic variants in KCNC1. In most individuals with KCNC1-related disorders, the pathogenic KCNC1 variant occurred spontaneously (de novo) and was not inherited from either parent.
Epidemiology[]
PME accounts for less than 1% of epilepsy cases at specialist centres.[citation needed] The incidence and prevalence of PME is unknown, but there are considerable geography and ethnic variations amongst the specific genetic disorders. One cause, Unverricht Lundborg Disease, has an incidence of at least 1:20,000 in Finland.[5]
See also[]
References[]
- ^ Berg AT, Berkovic SF, Brodie MJ, et al. (April 2010). "Revised terminology and concepts for organization of seizures and epilepsies: report of the ILAE Commission on Classification and Terminology, 2005-2009". Epilepsia. 51 (4): 676–85. doi:10.1111/j.1528-1167.2010.02522.x. PMID 20196795.
- ^ Bhat, Shweta; Ganesh, Subramaniam (2018-08-03). "New discoveries in progressive myoclonus epilepsies: a clinical outlook". Expert Review of Neurotherapeutics. 18 (8): 649–667. doi:10.1080/14737175.2018.1503949. ISSN 1473-7175. PMID 30032677.
- ^ Wirrell, Elaine (2016). "Infantile, Childhood, and Adolescent Epilepsies". CONTINUUM: Lifelong Learning in Neurology. 22 (1, Epilepsy): 60–93. doi:10.1212/con.0000000000000269. PMID 26844731.
- ^ Genton P (2006). "[Unverricht-Lundborg disease (PME1)]". Rev. Neurol. (Paris) (in French). 162 (8–9): 819–26. doi:10.1016/S0035-3787(06)75084-6. PMID 17028542.
- ^ "Unverricht-Lundborg Disease". Retrieved 2008-01-26.
External links[]
| Classification |
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- Epilepsy types