Juvenile myoclonic epilepsy

What it is, symptoms and effects

From: MedlinePlus Genetics, National Library of Medicine

Juvenile myoclonic epilepsy is a condition characterized by recurrent seizures (epilepsy). This condition begins in childhood or adolescence, usually between ages 12 and 18, 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, stress, or alcohol consumption.

Causes and biological mechanisms

From: MedlinePlus Genetics, National Library of Medicine

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.

Inheritance and family implications

From: MedlinePlus Genetics, National Library of Medicine

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.

How common is it?

From: MedlinePlus Genetics, National Library of Medicine

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

Reported clinical features and what the terms mean

The following findings are associated with this condition in Orphanet. They are not a checklist for diagnosing yourself, and they do not all occur in every affected person. Some are examination, imaging or laboratory findings that cannot be recognised at home.

The frequency labels describe how often a finding was reported among people with the condition in the source. They do not give the chance that a person with that symptom has the condition. Definitions below reproduce HPO terminology; they explain the term, not the likely severity in an individual.

EEG with polyspike wave complexes · Very frequent (99-80%)

The presence of complexes of repetitive spikes and waves in EEG.

Generalized-onset seizure · Very frequent (99-80%)

A generalized-onset seizure is a type of seizure originating at some point within, and rapidly engaging, bilaterally distributed networks. The networks may include cortical and subcortical structures but not necessarily the entire cortex.

Morning myoclonic jerks · Very frequent (99-80%)

Abnormality of eye movement · Frequent (79-30%)

An abnormality in voluntary or involuntary eye movements or their control.

Abnormality of the mouth · Frequent (79-30%)

An abnormality of the mouth.

Febrile seizure (within the age range of 3 months to 6 years) · Occasional (29-5%)

A febrile seizure is any type of seizure (most often a generalized tonic-clonic seizure) occurring with fever (at least 38 degrees Celsius) but in the absence of central nervous system infection, severe metabolic disturbance or other alternative precipitant in children between the ages of 3 months and 6 years.

Generalized non-motor (absence) seizure · Occasional (29-5%)

A generalized non-motor (absence) seizure is a type of a type of dialeptic seizure that is of electrographically generalized onset. It is a generalized seizure characterized by an interruption of activities, a blank stare, and usually the person will be unresponsive when spoken to. Any ictal motor phenomena are minor in comparison to these non-motor features.

Photosensitive tonic-clonic seizures · Occasional (29-5%)

Generalized-onset tonic-clonic seizures that are provoked by flashing or flickering light.

Other findings in the same source

From: Orphanet

Additional reported features include Aggressive behavior (Very rare (<4-1%)); Status epilepticus (Very rare (<4-1%)). This is a selected summary, not a complete description of the condition.

Which doctor should you see?

The suggested department for discussing Juvenile myoclonic epilepsy is Neurology, with a neurologist as the relevant type of clinician. General physician / Family Medicine; paediatrician for children. Referral depends on symptoms.

Additional services that may be relevant, depending on the findings, include: Clinical Genetics.

This is an editorial referral starting point. The appropriate clinic depends on the person’s age, symptoms, previous diagnosis and local services. The first clinician can decide whether another specialty or a team is needed; a department label does not confirm the diagnosis.

How to prepare for an assessment

Bring a short timeline of the main symptoms: when they first appeared, whether they are constant or episodic, what seems to change them, and how they affect daily activities. Include previous reports, discharge summaries, current medicines and supplements, allergies, and any relevant family history. A dated record is more useful than trying to match every feature in an online article.

Ask the clinician what is already established and what remains uncertain. If a test is suggested, ask what question it answers, what its limitations are and how the result would change the next step. The information here is not an instruction to arrange every possible test. In children, bring growth, developmental and school information if it is relevant to the concern.

• Which nervous-system findings help explain the symptoms?
• Would an assessment of walking, communication or daily function be helpful?
• Are rehabilitation or other specialist services relevant?

Treatment discussions and follow-up

The material gathered for this draft does not provide a complete condition-specific treatment pathway for Juvenile myoclonic epilepsy. That gap does not mean that treatment is unavailable. A clinician needs to establish the diagnosis and review current guidance before recommending medicines, procedures, rehabilitation or other support.

Before leaving the appointment, clarify the next review date, who will communicate results, and whom to contact if the situation changes. Discuss difficulties with sleep, work, school, mobility, eating or emotional wellbeing when these are relevant. Practical support may require coordination between the treating clinician and other services.

The collected references do not establish a complete prevention or long-term outlook section for this entry. Missing information should not be interpreted as proof that prevention is impossible or that a particular outcome is inevitable. Ask what is known for the exact subtype, stage and personal circumstances, and which uncertainties remain.

When to seek emergency help

Severe breathing difficulty, collapse, new stroke-like symptoms, a seizure that is prolonged or repeated without recovery, uncontrolled major bleeding, or an immediate risk of self-harm require emergency help. In India, call 112 or reach the nearest emergency department. This is a general, non-exhaustive warning list; it is not a condition-specific triage tool.