Myoclonic Absence Seizures in Dravet Syndrome

Atypical absence seizures and gene variants: A gene-based review of etiology, electro-clinical features, and associated epilepsy syndrome

Atypical absence seizures are generalized non-convulsive seizures that often occur in children with cognitive impairment. They are common in refractory epilepsy and have been recognized as one of the hallmarks of developmental epileptic encephalopathies. Notably, pathogenic variants associated with AAS, such as GABRG2, GABRG3, SLC6A1, CACNB4, SCN8A, and SYNGAP1, are also linked to developmental epileptic encephalopathies. Atypical absences differ from typical absences in that they are frequently drug-resistant and the prognosis is dependent on the etiology or related epileptic syndromes. To improve clinicians' understanding of atypical absences and provide novel perspectives for clinical treatment, we have reviewed the electro-clinical characteristics, etiologies, treatment, and prognosis of atypical absences, with a focus on the etiology of advancements in gene variants, shedding light on potential avenues for improved clinical management.

A case of Dravet syndrome with focal cortical myoclonus

Background

Dravet syndrome (DS) is a severe epileptic encephalopathy in children dominated by polymorphic seizures. Focal cortical myoclonus indicated on conventional electroencephalogram (EEG) was rarely observed in DS.

Case presentation

The child, boy, thirteen months old, suffered from clonic seizures during bathing at two months old. Later he suffered from recurrent afebrile or febrile generalized tonic–clonic seizures often developing into status epilepticus. A genetic analysis of the SCN1A gene revealed a de novo heterozygous frame shift mutation in exon 21(c.3836_c.3837del AT).His myoclonic jerks of unilateral arm occurred spontaneously in response to movement. A spike wave from right central-parietal cortex immediately preceded a left myoclonic muscle activity, while a spike wave from left immediately preceded a right myoclonic muscle activity. The onset of the detected spike preceded the onset of myoclonic muscle activity by 42 ms using jerk-locked back-averaging of electroencephalogram data. The focal cortical myoclonus was not noted when one year old.

Conclusions

Focal cortical myoclonus could be a form of seizures during the first year of life in DS, which may broaden the types of seizures of DS and may provide some diagnostic clues for DS.

International League Against Epilepsy classification and definition of epilepsy syndromes with onset in childhood: Position paper by the ILAE Task Force on Nosology and Definitions

The 2017 International League Against Epilepsy classification has defined a three-tier system with epilepsy syndrome identification at the third level. Although a syndrome cannot be determined in all children with epilepsy, identification of a specific syndrome provides guidance on management and prognosis. In this paper, we describe the childhood onset epilepsy syndromes, most of which have both mandatory seizure type(s) and interictal electroencephalographic (EEG) features. Based on the 2017 Classification of Seizures and Epilepsies, some syndrome names have been updated using terms directly describing the seizure semiology. Epilepsy syndromes beginning in childhood have been divided into three categories: (1) self-limited focal epilepsies, comprising four syndromes: self-limited epilepsy with centrotemporal spikes, self-limited epilepsy with autonomic seizures, childhood occipital visual epilepsy, and photosensitive occipital lobe epilepsy; (2) generalized epilepsies, comprising three syndromes: childhood absence epilepsy, epilepsy with myoclonic absence, and epilepsy with eyelid myoclonia; and (3) developmental and/or epileptic encephalopathies, comprising five syndromes: epilepsy with myoclonic-atonic seizures, Lennox-Gastaut syndrome, developmental and/or epileptic encephalopathy with spike-and-wave activation in sleep, hemiconvulsion-hemiplegia-epilepsy syndrome, and febrile infection-related epilepsy syndrome. We define each, highlighting the mandatory seizure(s), EEG features, phenotypic variations, and findings from key investigations.

Visually sensitive seizures: An updated review by the Epilepsy Foundation

Light flashes, patterns, or color changes can provoke seizures in up to 1 in 4000 persons. Prevalence may be higher because of selection bias. The Epilepsy Foundation reviewed light-induced seizures in 2005. Since then, images on social media, virtual reality, three-dimensional (3D) movies, and the Internet have proliferated. Hundreds of studies have explored the mechanisms and presentations of photosensitive seizures, justifying an updated review. This literature summary derives from a nonsystematic literature review via PubMed using the terms "photosensitive" and "epilepsy." The photoparoxysmal response (PPR) is an electroencephalography (EEG) phenomenon, and photosensitive seizures (PS) are seizures provoked by visual stimulation. Photosensitivity is more common in the young and in specific forms of generalized epilepsy. PS can coexist with spontaneous seizures. PS are hereditable and linked to recently identified genes. Brain imaging usually is normal, but special studies imaging white matter tracts demonstrate abnormal connectivity. Occipital cortex and connected regions are hyperexcitable in subjects with light-provoked seizures. Mechanisms remain unclear. Video games, social media clips, occasional movies, and natural stimuli can provoke PS. Virtual reality and 3D images so far appear benign unless they contain specific provocative content, for example, flashes. Images with flashes brighter than 20 candelas/m² at 3-60 (particularly 15-20) Hz occupying at least 10 to 25% of the visual field are a risk, as are red color flashes or oscillating stripes. Equipment to assay for these characteristics is probably underutilized. Prevention of seizures includes avoiding provocative stimuli, covering one eye, wearing dark glasses, sitting at least two meters from screens, reducing contrast, and taking certain antiseizure drugs. Measurement of PPR suppression in a photosensitivity model can screen putative antiseizure drugs. Some countries regulate media to reduce risk. Visually-induced seizures remain significant public health hazards so they warrant ongoing scientific and regulatory efforts and public education.

De novo variants in SETD1B cause intellectual disability, autism spectrum disorder, and epilepsy with myoclonic absences

Epilepsy with myoclonic absences is a specific seizure type characterized by bilateral rhythmic clonic jerks with impairment of consciousness. Here, we report an individual with epilepsy with myoclonic absences, mild intellectual disabilities, language disorder, and autism spectrum disorder. His interictal electroencephalogram revealed a spike-and-slow wave complex dominant in the frontal area. His ictal polygraphic and video-electroencephalogram showed a characteristic diffuse synchronous 3-Hz spike-and-wave burst associated with bilateral upper limb myoclonic jerks with impairment of consciousness. Using whole-exome sequencing, we found a novel de novo variant, c.386T>G, p.(Val129Gly), in SETD1B (SET domain containing 1B). We previously reported that two individuals with a de novo SETD1B variant showed intellectual disability, epilepsy, and autism. Of note, one of those individuals and the present case showed epilepsy with myoclonic absences. Therefore, this report supports the indication that SETD1B may be a causative gene for neurodevelopmental disorders and suggests that epilepsy with myoclonic absences may be a characteristic feature of SETD1B-related disorders.

Myoclonic absence seizures with complex gestural automatisms

Epilepsy with myoclonic absences is a rare generalized epilepsy syndrome with distinctive seizures. Two unrelated children had mild developmental impairment and onset of myoclonic-absences at 3 and 8 years. Seizures were characterized by bilateral 3 Hz myoclonic jerks superimposed on tonic abduction of the upper limbs. Events lasted 10-60 s, and complex gestural automatisms were often observed; in one case, a boy undid his seatbelt and attempted to exit a moving vehicle. Post-ictally, both children immediately regained awareness without recollection of their actions. Ictal EEGs showed 3 Hz generalized spike-wave. Complex automatisms have not been described in myoclonic absence seizures. This generalized seizure type can be confused with focal seizures when these ictal behaviours occur.