Juvenile myoclonic epilepsy

A fairly common form of idiopathic generalized epilepsy, representing 5-10% of all epilepsy cases.

Typically manifests between the ages of 12 and 18 with brief episodes of involuntary muscle twitching occurring early in the morning.

Most patients also have generalized seizures affecting the entire brain and many also have absence seizures.

There are at least 6 loci, 4 with known causative genes.

Most of these genes are ion channels with the one non-ion channel gene having been shown to affect ion channel currents.

Episodes of involuntary muscle twitching occurring early in the morning or shortly before falling asleep.

Muscle twitching episodes are more common in the arms than in the legs, resulting in dropping objects.

Generalized tonic-clonic and absence seizures can also occur.

Quick jerking movements in the morning that often results in knocking over objects around them.

Clusters of myoclonic seizures can lead to absence seizures.

Clusters of absence seizures can lead to generalized tonic-clonic seizures.

Symptoms starts generally around age 10-16 years, although some patients can present in their 20s or even early 30s.

The myoclonic jerks generally precede the generalized tonic-clonic seizures by several months.

Some, however, never develop generalized tonic-clonic seizures.

Sleep deprivation is a major factor in triggering generalized tonic-clonic seizures.

Patients, generally do not have other neurological problems.

Juvenile myoclonic epilepsy is an inherited genetic syndrome, with 17-49% having relatives with a history of epileptic seizures.

CACNB4 is a gene that encodes the calcium channel β subunit protein.

These β subunits are helpful regulators of calcium channel current amplitude, voltage dependence, and also regulate channel trafficking.

The β4 isoform encoded by CACNB4 is most prevalent in the cerebellum.

There are at least two mutations in the β4 subunit associated with JME, C104F and R482X.

CLCN2 gene encodes a chloride channel important in maintaining a proper chloride reversal potential needed in inhibitory neurotransmission by GABA.

GABRD and EFHC1 gene mutations rarely associated with JME.

It may be a ciliopathy.

Diagnosis is made based on history.

The physical examination should be normal.

Myoclonic jerks, which are the hallmark of the syndrome.

An electroencephalogram (EEG) has a pattern of waves and spikes associated with the syndrome.

The EEG shows a very characteristic pattern with generalized 4–6 Hz polyspike and slow wave discharges, often provoked by photic stimulation and sometimes hyperventilation.

Brain MRI and brain CT are normal.


The most effective anti-epileptic medication for JME is valproic acid (Depakote).

Lamotrigine, levetiracetam, topiramate, and zonisamide are alternative anti-epileptic medications.

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