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 reappraisal of atypical absence seizures in children and adults: therapeutic implications.

Introduction: Atypical absences are generalized epileptic seizures typically affecting children with severe epilepsies and learning difficulties along with other seizure types. Video-EEG is essential for their diagnosis. Recently, atypical absence seizures have been reported as a hallmark of some developmental and epileptic encephalopathies.Areas covered: This is a narrative review of the literature which describes the electroclinical features of atypical seizures, the characteristics of developmental epileptic encephalopathies in which this seizure type can occur, and the evidence supporting the use of individual antiseizure drugs for the treatment of atypical absences.Expert opinion: Treatment of absence seizures typically relies on ethosuximide (ineffective against tonic-clonic seizures), valproate (associated with larger proportion of adverse events), or lamotrigine (less effective than the other two). However, unlike typical absences, atypical absences are usually intractable, persist lifetime, and their prognosis depends on the underlying etiology or associated epilepsy syndrome. Besides efficacy, other relevant factors, such as drug formulation, ease of titration and dosing, and drug interactions, should be considered. Drugs that may worsen epilepsy, cognition and behavior should be avoided. In the vast majority of patients, a polytherapy is required, although usually with limited efficacy. Finally, epilepsy syndromes featuring atypical absences require a multidisciplinary approach.

Neonatal exposure to AY-9944 increases typical spike and wave discharges in WAG/Rij and Wistar rats.

Absence-epileptic seizures appear in the EEG as Spike and Wave Discharges (SWDs). Typical SWDs develop spontaneously in WAG/Rij rats, an inbred Wistar strain. Atypical SWDs however were reported in studies in which the cholesterol synthesis inhibitor AY-9944 was administered to neonatal Wistar rats, causing absence-like seizures later in life. Atypical SWDs seemed to differ from typical SWDs in 3 aspects: lower peak frequency, longer duration, and involvement of the hippocampus. The aim of the present study was to investigate the effect of AY-9944 on typical SWDs. Male Wistar and WAG/Rij rats were injected with 7.5 mg/kg AY-9944 or saline postnatally. After 6 months, EEGs were recorded from the cortex and the hippocampus. Incidence, duration and peak frequency of the SWDs were determined. The SWD stopping probability was estimated by hazard rate analysis. Hippocampal involvement was assessed by cross correlation analysis of the hippocampus and cortex channels. The Wistar rats unexpectedly showed a high incidence of spontaneous SWDs. The AY-treatment increased the total SWD duration in both Wistar and WAG/Rij rats: the incidence was 1.6 times higher and the mean SWD duration was 1.4 times longer than in the saline-treated rats. The peak frequency of the SWDs did not change. The hazard rates were lower in the AY-treated rats, so some very long SWDs were observed. Cross correlations of spiky activity in the hippocampus pointed to volume conduction rather than to genuine SWD activity in this area. In summary, we found no indication that SWDs in AY-treated animals differ from typical SWDs. However, since saline-treated rats had many spontaneous SWDs, other rat strains might respond differently. With respect to the mechanism, the appearance of long SWDs suggests that the SWD stopping mechanism is affected by the treatment. We speculate that this effect is due to changes in the distribution of GABA-ergic and glutamatergic receptors in lipid rafts.