This is characterized by ataxia and lethargic behavior at early stages of development followed within days by the onset of both focal motor seizures as well as episodes of behavioral immobility which correlates with patterns of cortical spike and wave discharges at the EEG A premature-termination mutation R482X was identified in a patient with JME while an additional missense mutation C104F was identified in a German family with generalized epilepsy and praxis – induced seizures.The R482X mutation results in increased current amplitudes and an accelerated fast time constant of inactivation. Whether these modest functional differences may be in charge of JME remains to be established. Calcium channel β4 subunit (CACNB4) is not strictly considered a putative JME gene because its mutation did not segregate in affected family members, and it was found in only one member of a JME family from Germany, and it has not been replicated. GABRA1
GABRA1 is a gene that encodes for an α subunit of the GABA A receptor protein, which encodes one of the major inhibitory neurotransmitter receptors. There is one known mutation in this gene that is associated with JME, A322D, which is located in the third segment of the protein. This missense mutation results in channels with reduced peak GABA-evoked currents. Furthermore, the presence of such mutation alters the composition and reduces the expression of wild-type GABAA receptors. GABRD
GABRD encodes the δ subunit of the GABA receptor, which is an important constituent of the GABAA receptor mediating tonic inhibition in neurons (extrasynaptic GABA receptors, i.e.
A long-term population-based study suggested that at 25 years from seizure onset all seizure types in JME resolved in 17% and in 13% only myoclonus remained despite discontinuing medication. Thus, disabling seizures resolve in around one-third of patients. Signs and symptoms
There are three principle seizures types which may occur in JME: myoclonus, generalized tonic-clonic seizures and absence seizures. Approximately one-third of patients have all three seizure types. The majority of patients (58.2%) have frequent myoclonic jerks and uncommon generalized tonic-clonic seizures. Absence seizures are believed to be the least common with studies estimating a prevalence of 10% to as high as 38%. Myoclonic status epilepticus may occur as a complication but it is uncommon. Patient’s typically initially present to medical providers following their first generalized tonic-clonic seizure. It is often subsequently reported that the patient was having myoclonus for several years prior. The first generalized tonic-clonic seizure usually occurs in the context of a particular provoking factor such as sleep deprivation, stress or alcohol consumption. There are other potential provoking factors such as praxis induction which refers to the precipitation of seizures or epileptiform discharges in the context of a complex cognitive tasks. Patients with JME tend to perform worse on neuropsychological assessments in multiple cognitive domains and are also more likely to have psychiatric comorbidities such as depression and anxiety when compared to control populations. The majority of patients with JME report satisfaction with their health, work, friendships and social life.