Epilepsy with myoclonic absences (ORPHA:86911)
A rare childhood-onset epilepsy characterized by sudden onset, short lasting absence associated with rhythmical myoclonia of head and shoulders.
Epidemiology
Exact incidence of this rare epilepsy syndrome is unknown. Both sexes are affected, with a male predominance (70%).
Clinical description
Seizure onset is between 1 to 12 years of age (peak 7 years) and characterized by absences associated with rhythmical jerks of head/shoulders. Other seizure types (generalized tonic-clonic, atonic seizures and typical absences) occur in the majority of patients. At presentation, approximately half the children are developmentally and neurologically normal; a spectrum of learning disability is eventually seen in 70% of cases.
Etiology
Currently, the etiology is unidentified in the majority of cases. In 30% of cases, a genetic cause can be found with possible polygenic etiologies. SLC2A1 variants (1p34.2), causing GLUT1 deficiency, are one of the most common monogenic etiologies of myoclonic absences. There is one case report of a translocation resulting in a truncation in the SYNGAP1 gene causing epilepsy with myoclonic absences. A family history (usually of generalized seizures) is present in 20% of cases. Rarely, there is a family history of febrile seizures.
Diagnostic methods
Micro-array and dedicated epilepsy panels can show pathogenic mutations. On electroencephalogram (EEG), generalized spike-and-wave discharges and polyspike-and-wave discharges may occur. Background is otherwise normal. Ictal EEG: regular 3-Hz generalized spike-and-wave accompanies myoclonic absences. Electromyography recordings from the upper arm show a constant relationship between the bilateral myoclonic jerks and spike-and-waves. High resolution magnetic resonance imaging is required to exclude structural brain abnormality although neuroimaging is usually normal. However, mild non-specific diffuse atrophy is seen in some cases.
Differential diagnosis
Differential diagnosis includes Lennox-Gastaut syndrome (atypical absences may occur with rhythmic myoclonic jerking but EEG background is typically abnormal), myoclonic seizures due to structural brain abnormality, childhood absence epilepsy with a common EEG pattern but the description of the seizure is different, progressive myoclonic epilepsies, and myoclonic atonic epilepsy.
Antenatal diagnosis
Not relevant.
Genetic counseling
In case of a monogenic etiology or a chromosomal anomaly, genetic counseling can be provided.
Management and treatment
Seizures are often difficult to treat and may continue into adulthood. Anti-seizure drugs for absence seizures can be used: sodium valproate, ethosuximide, zonisamide, topiramate, or levetiracetam.
Prognosis
Seizures are usually difficult to control. Later on, in adolescence and adulthood, other (generalized) seizures may develop in almost half of patients. Sometimes an evolution towards juvenile myoclonic epilepsy is seen. Cognitive function seems to be preserved in children in whom myoclonic absences are controlled.

                            Last update: 
                            December 2021


                            - Expert reviewer(s): 
                            Pr Lieven LAGAE | EpiCARE* - Pr Rima NABBOUT | EpiCARE* - Pr Sylvie NGUYEN | EpiCARE*


                                * European Reference Network