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Juvenile myoclonic epilepsy

Reviewed June 2012

What is juvenile myoclonic epilepsy?

Juvenile myoclonic epilepsy is a condition characterized by recurrent seizures (epilepsy). This condition begins in childhood or adolescence, usually between ages 8 and 20, and lasts into adulthood. The most common type of seizure in people with this condition is myoclonic seizures, which cause rapid, uncontrolled muscle jerks. People with this condition may also have generalized tonic-clonic seizures (also known as grand mal seizures), which cause muscle rigidity, convulsions, and loss of consciousness. Sometimes, affected individuals have absence seizures, which cause loss of consciousness for a short period that appears as a staring spell. Typically, people with juvenile myoclonic epilepsy develop the characteristic myoclonic seizures in adolescence, then develop generalized tonic-clonic seizures a few years later. Although seizures can happen at any time, they occur most commonly in the morning, shortly after awakening. Seizures can be triggered by a lack of sleep, extreme tiredness, or alcohol consumption.

How common is juvenile myoclonic epilepsy?

Juvenile myoclonic epilepsy affects an estimated 1 in 1,000 people worldwide. Approximately 5 percent of people with epilepsy have juvenile myoclonic epilepsy.

What genes are related to juvenile myoclonic epilepsy?

The genetics of juvenile myoclonic epilepsy are complex and not completely understood. Mutations in one of several genes can cause or increase susceptibility to this condition. The most studied of these genes are the GABRA1 gene and the EFHC1 gene, although mutations in at least three other genes have been identified in people with this condition. Many people with juvenile myoclonic epilepsy do not have mutations in any of these genes. Changes in other, unidentified genes are likely involved in this condition.

A mutation in the GABRA1 gene has been identified in several members of a large family with juvenile myoclonic epilepsy. The GABRA1 gene provides instructions for making one piece, the alpha-1 (α1) subunit, of the GABAA receptor protein. The GABAA receptor acts as a channel that allows negatively charged chlorine atoms (chloride ions) to cross the cell membrane. After infancy, the influx of chloride ions creates an environment in the cell that inhibits signaling between nerve cells (neurons) and prevents the brain from being overloaded with too many signals. Mutations in the GABRA1 gene lead to an altered α1 subunit and a decrease in the number of GABAA receptors available. As a result, the signaling between neurons is not controlled, which can lead to overstimulation of neurons. Researchers believe that the overstimulation of certain neurons in the brain triggers the abnormal brain activity associated with seizures.

Mutations in the EFHC1 gene have been associated with juvenile myoclonic epilepsy in a small number of people. The EFHC1 gene provides instructions for making a protein that also plays a role in neuron activity, although its function is not completely understood. The EFHC1 protein is attached to another protein that acts as a calcium channel. This protein allows positively charged calcium ions to cross the cell membrane. The movement of these ions is critical for normal signaling between neurons. The EFHC1 protein is thought to help regulate the balance of calcium ions inside the cell, although the mechanism is unclear. In addition, studies show that the EFHC1 protein may be involved in the self-destruction of cells. EFHC1 gene mutations reduce the function of the EFHC1 protein. Researchers suggest that this reduction causes an increase in the number of neurons and disrupts the calcium balance. Together, these effects may lead to overstimulation of neurons and trigger seizures.

Related Gene(s)

Changes in these genes are associated with juvenile myoclonic epilepsy.

  • CACNB4
  • CLCN2
  • EFHC1
  • GABRA1
  • GABRD

How do people inherit juvenile myoclonic epilepsy?

The inheritance pattern of juvenile myoclonic epilepsy is not completely understood. When the condition is caused by mutations in the GABRA1 gene, it is inherited in an autosomal dominant pattern, which means one copy of the altered gene in each cell is sufficient to cause the disorder. The inheritance pattern of juvenile myoclonic epilepsy caused by mutations in the EFHC1 gene is not known.

Although juvenile myoclonic epilepsy can run in families, many cases occur in people with no family history of the disorder.

Where can I find information about diagnosis or management of juvenile myoclonic epilepsy?

These resources address the diagnosis or management of juvenile myoclonic epilepsy and may include treatment providers.

  • Genetic Testing Registry: Epilepsy, idiopathic generalized 10 (http://www.ncbi.nlm.nih.gov/gtr/conditions/C2751603)
  • Genetic Testing Registry: Epilepsy, idiopathic generalized 9 (http://www.ncbi.nlm.nih.gov/gtr/conditions/C2750887)
  • Genetic Testing Registry: Epilepsy, juvenile myoclonic 5 (http://www.ncbi.nlm.nih.gov/gtr/conditions/C2749942)
  • Genetic Testing Registry: Epilepsy, juvenile myoclonic 9 (http://www.ncbi.nlm.nih.gov/gtr/conditions/CN116435)
  • Genetic Testing Registry: Epilepsy with grand mal seizures on awakening (http://www.ncbi.nlm.nih.gov/gtr/conditions/C0393697)
  • Genetic Testing Registry: Juvenile myoclonic epilepsy (http://www.ncbi.nlm.nih.gov/gtr/conditions/C1850778)
  • Merck Manual Home Health Edition: Seizure Disorders (http://www.merckmanuals.com/home/brain_spinal_cord_and_nerve_disorders/seizure_disorders/seizure_disorders.html?qt=&sc=&alt=)

You might also find information on the diagnosis or management of juvenile myoclonic epilepsy in Educational resources (http://www.ghr.nlm.nih.gov/condition/juvenile-myoclonic-epilepsy/show/Educational+resources) and Patient support (http://www.ghr.nlm.nih.gov/condition/juvenile-myoclonic-epilepsy/show/Patient+support).

General information about the diagnosis (http://ghr.nlm.nih.gov/handbook/consult/diagnosis) and management (http://ghr.nlm.nih.gov/handbook/consult/treatment) of genetic conditions is available in the Handbook. Read more about genetic testing (http://ghr.nlm.nih.gov/handbook/testing), particularly the difference between clinical tests and research tests (http://ghr.nlm.nih.gov/handbook/testing/researchtesting).

To locate a healthcare provider, see How can I find a genetics professional in my area? (http://ghr.nlm.nih.gov/handbook/consult/findingprofessional) in the Handbook.

Where can I find additional information about juvenile myoclonic epilepsy?

You may find the following resources about juvenile myoclonic epilepsy helpful. These materials are written for the general public.

You may also be interested in these resources, which are designed for healthcare professionals and researchers.

What other names do people use for juvenile myoclonic epilepsy?

  • adolescent myoclonic epilepsy
  • Janz syndrome
  • petit mal, impulsive

For more information about naming genetic conditions, see the Genetics Home Reference Condition Naming Guidelines (http://ghr.nlm.nih.gov/ConditionNameGuide) and How are genetic conditions and genes named? (http://ghr.nlm.nih.gov/handbook/mutationsanddisorders/naming) in the Handbook.

What if I still have specific questions about juvenile myoclonic epilepsy?

Ask the Genetic and Rare Diseases Information Center (http://rarediseases.info.nih.gov/GARD/).

What glossary definitions help with understanding juvenile myoclonic epilepsy?

adolescent ; autosomal ; autosomal dominant ; calcium ; cell ; cell membrane ; channel ; chloride ; epilepsy ; family history ; GABA ; gene ; genetics ; idiopathic ; inheritance ; inheritance pattern ; inherited ; ions ; juvenile ; mutation ; neuron ; protein ; receptor ; seizure ; subunit ; susceptibility ; syndrome

You may find definitions for these and many other terms in the Genetics Home Reference Glossary (http://www.ghr.nlm.nih.gov/glossary).

References

  • Cossette P, Liu L, Brisebois K, Dong H, Lortie A, Vanasse M, Saint-Hilaire JM, Carmant L, Verner A, Lu WY, Wang YT, Rouleau GA. Mutation of GABRA1 in an autosomal dominant form of juvenile myoclonic epilepsy. Nat Genet. 2002 Jun;31(2):184-9. Epub 2002 May 6. (http://www.ncbi.nlm.nih.gov/pubmed/11992121?dopt=Abstract)
  • Ding L, Feng HJ, Macdonald RL, Botzolakis EJ, Hu N, Gallagher MJ. GABA(A) receptor alpha1 subunit mutation A322D associated with autosomal dominant juvenile myoclonic epilepsy reduces the expression and alters the composition of wild type GABA(A) receptors. J Biol Chem. 2010 Aug 20;285(34):26390-405. doi: 10.1074/jbc.M110.142299. Epub 2010 Jun 15. (http://www.ncbi.nlm.nih.gov/pubmed/20551311?dopt=Abstract)
  • Gallagher MJ, Ding L, Maheshwari A, Macdonald RL. The GABAA receptor alpha1 subunit epilepsy mutation A322D inhibits transmembrane helix formation and causes proteasomal degradation. Proc Natl Acad Sci U S A. 2007 Aug 7;104(32):12999-3004. Epub 2007 Aug 1. (http://www.ncbi.nlm.nih.gov/pubmed/17670950?dopt=Abstract)
  • Krampfl K, Maljevic S, Cossette P, Ziegler E, Rouleau GA, Lerche H, Bufler J. Molecular analysis of the A322D mutation in the GABA receptor alpha-subunit causing juvenile myoclonic epilepsy. Eur J Neurosci. 2005 Jul;22(1):10-20. (http://www.ncbi.nlm.nih.gov/pubmed/16029191?dopt=Abstract)
  • Suzuki T, Delgado-Escueta AV, Aguan K, Alonso ME, Shi J, Hara Y, Nishida M, Numata T, Medina MT, Takeuchi T, Morita R, Bai D, Ganesh S, Sugimoto Y, Inazawa J, Bailey JN, Ochoa A, Jara-Prado A, Rasmussen A, Ramos-Peek J, Cordova S, Rubio-Donnadieu F, Inoue Y, Osawa M, Kaneko S, Oguni H, Mori Y, Yamakawa K. Mutations in EFHC1 cause juvenile myoclonic epilepsy. Nat Genet. 2004 Aug;36(8):842-9. Epub 2004 Jul 18. (http://www.ncbi.nlm.nih.gov/pubmed/15258581?dopt=Abstract)

 

The resources on this site should not be used as a substitute for professional medical care or advice. Users seeking information about a personal genetic disease, syndrome, or condition should consult with a qualified healthcare professional. See How can I find a genetics professional in my area? (http://ghr.nlm.nih.gov/handbook/consult/findingprofessional) in the Handbook.

 
Reviewed: June 2012
Published: November 24, 2014