Juvenile myoclonic epilepsy (JME), also known as Janz syndrome, is a common form of genetic generalized epilepsy (previously known as idiopathic generalized epilepsy), representing 5-10% of all epilepsy cases. This disorder typically first presents between the ages of 12 and 18 with myoclonic seizure manifesting as sudden brief involuntary single or multiple episodes of muscle(s) contractions caused by an abnormal excessive or synchronous neuronal activity in the brain. These events typically occur after awakening from sleep, during the evening or upon sleep deprivation. JME is also characterized by generalized tonic-clonic seizures and a minority also have absence seizures. The genetics of JME are complex and rapidly evolving as over 20 chromosomal loci and multiple genes have been identified thus far. Given the genetic and clinical heterogeneity of JME some authors have suggested that it should be thought of as a spectrum disorder. Epidemiology
The prevalence of JME is approximately 0.1-0.2 per 100,000 and constitutes approximately 5-10% of all epilepsies. Some studies suggest that JME is slightly more common in females than males. The onset of symptoms ranges between the ages of 8 and 36 years and has a peak between the ages of 12 and 18 years. Approximately 15% of children with childhood absence epilepsy and juvenile absence epilepsy subsequently develop JME. In most cases, myoclonic jerks precede the first generalized tonic-clonic seizure by a mean of 3.3 years.
receptors that are localized outside of the synapse). Among the mutations that have been reported in this in this gene, one (R220H) has been identified in a small family with JME. This mutation affects GABAergic transmission by altering the surface expression of the receptor as well as reducing the channel – opening duration. Myoclonin1/EFHC1
The final known associated gene is EFHC1. Myoclonin1/EFHC1 encodes for a protein that has been known to play a wide range of wild-type cell division, neuroblast migration and synapse/dendrite formation. EFHC1 is expressed in many tissues, including the brain, where it is localized to the soma and dendrites of neurons, particularly the hippocampal CA1 region, pyramidal neurons in the cerebral cortex, and Purkinje cells in the cerebellum.There are four JME-causing mutations discovered (D210N, R221H, F229L and D253Y). The mutations do not seem to alter the ability of the protein to colocalize with centrosomes and mitotic spindles but induce mitotic spindle defects. Moreover, the mutations impact radial and tangential migration during brain development. As such a theory has been put forward that JME may be the result of a brain developmental disorder. Other loci
Three SNP alleles in BRD2, Cx-36 and ME2 and microdeletions in 15q13.3, 15q11.2 and 16p.13.11 also contribute risk to JME. Diagnosis
Diagnosis is typically made based on patient history. The physical examination is usually normal. The primary diagnosis for JME is a good knowledge of patient history  and the neurologists familiarity with the myoclonic jerks, which are the hallmark of the syndrome.