Clinical dissection of early onset absence epilepsy in children and prognostic implications

Early onset absence epilepsy of childhood: Epidemiologic data, treatment and outcome in a sample of 56 patients born between 2000 and 2018

PURPOSE

The aim of our work is to describe the characteristics of Early Onset Absence Epilepsy (EOAE) and to observe whether specific anamnestic, clinical or electroencephalographic characteristics can influence the drug sensitivity of this pathology.

METHODS

We carried out a retrospective study of patients affected by absence epilepsy with onset under four years of age, born between January 1st 2000 and December 31st 2018, who were reffered to the Regional Epilepsy Center of Spedali Civili of Brescia. We then divided the sample into three groups based on the age of onset.

RESULTS

Our sample is composed of 56 patients. Among the children with epilepsy onset under two years of age (11), all were still on therapy after three and six years of follow-up, and 64 % of them required polytherapy. Among patients with epilepsy onset between two and three years of age (24), 87 % were still on therapy after three years of follow-up and 68 % after six years of follow-up; 46 % of these subjects required polytherapy. Among patients with epilepsy onset between three and four years of age (21), 89 % were still on therapy after three years of follow-up and 38 % after six years of follow-up; 38 % of them required polytherapy.

CONCLUSIONS

We observe that patients with an earlier epilepsy onset have a worse outcome and a lower drug sensitivity. This may allow to predict in which cases it would be appropriate to maintain antiseizure therapy for a prolonged period.

De novo SCN1A, SCN8A, and CLCN2 mutations in childhood absence epilepsy

This study aimed to identify monogenic mutations from Chinese patients with childhood absence epilepsy (CAE) and summarize their characteristics. A total of 100 patients with CAE were recruited in Peking University First Hospital from 2005 to 2016 and underwent telephone and outpatient follow-up review. We used targeted disease-specific gene capture sequencing (involving 300 genes) to identify pathogenic variations for these patients. We identified three de novo epilepsy-related gene mutations, including missense mutations of SCN1A (c. 5399 T > A; p. Val1800Asp), SCN8A (c. 2371 G > T; p. Val791Phe), and CLCN2 (c. 481 G > A; p. Gly161Ser), from three patients, separately. All recruited patients presented typical CAE features and good prognosis. To date, CAE has been considered a complex disease caused by multiple susceptibility genes. In this study, we observed that 3% of typical CAE patients had a de novo mutation of a known monogenic epilepsy-related gene. Our study suggests that a significant proportion of typical CAE cases may be monogenic forms of epilepsy. For genetic generalized epilepsies, such as CAE, further studies are needed to clarify the contributions of de novo or inherited rare monogenic coding, noncoding and copy number variants.

Glut1 deficiency is a rare but treatable cause of childhood absence epilepsy with atypical features

Glucose transporter type 1 deficiency syndrome (GLUT1-DS) is a rare genetic disorder caused by pathogenic variants in SLC2A1, resulting in impaired glucose uptake through the blood-brain barrier. Our objective is to analyze the frequency of GLUT1-DS in patients with absences with atypical features. Sequencing analysis and detection of copy number variation of the SLC2A1 gene was carried out in patients with atypical absences including: early-onset absence, intellectual disability, additional seizure types, refractory epilepsy, associated movement disorders, as well as those who have first-degree relatives with absence epilepsy or atypical EEG ictal discharges. Of the 43 patients analyzed, pathogenic variations were found in 2 (4.6%). Six atypical characteristics were found in these 2 patients. The greater the number of atypical characteristics presenting in patients with absence seizures, the more likely they have a SLC2A1 mutation. Although GLUT1-DS is an infrequent cause of absence epilepsy, recognizing this disorder is important, since initiation of a ketogenic diet can reduce the frequency of seizures, the severity of the movement disorder, and also improve the quality of life of the patients and their families.

Rare coding variants in genes encoding GABAA receptors in genetic generalised epilepsies: an exome-based case-control study

BACKGROUND

Genetic generalised epilepsy is the most common type of inherited epilepsy. Despite a high concordance rate of 80% in monozygotic twins, the genetic background is still poorly understood. We aimed to investigate the burden of rare genetic variants in genetic generalised epilepsy.

METHODS

For this exome-based case-control study, we used three different genetic generalised epilepsy case cohorts and three independent control cohorts, all of European descent. Cases included in the study were clinically evaluated for genetic generalised epilepsy. Whole-exome sequencing was done for the discovery case cohort, a validation case cohort, and two independent control cohorts. The replication case cohort underwent targeted next-generation sequencing of the 19 known genes encoding subunits of GABA_A receptors and was compared to the respective GABA_A receptor variants of a third independent control cohort. Functional investigations were done with automated two-microelectrode voltage clamping in Xenopus laevis oocytes.

FINDINGS

Statistical comparison of 152 familial index cases with genetic generalised epilepsy in the discovery cohort to 549 ethnically matched controls suggested an enrichment of rare missense (Nonsyn) variants in the ensemble of 19 genes encoding GABA_A receptors in cases (odds ratio [OR] 2·40 [95% CI 1·41-4·10]; p_Nonsyn=0·0014, adjusted p_Nonsyn=0·019). Enrichment for these genes was validated in a whole-exome sequencing cohort of 357 sporadic and familial genetic generalised epilepsy cases and 1485 independent controls (OR 1·46 [95% CI 1·05-2·03]; p_Nonsyn=0·0081, adjusted p_Nonsyn=0·016). Comparison of genes encoding GABA_A receptors in the independent replication cohort of 583 familial and sporadic genetic generalised epilepsy index cases, based on candidate-gene panel sequencing, with a third independent control cohort of 635 controls confirmed the overall enrichment of rare missense variants for 15 GABA_A receptor genes in cases compared with controls (OR 1·46 [95% CI 1·02-2·08]; p_Nonsyn=0·013, adjusted p_Nonsyn=0·027). Functional studies for two selected genes (GABRB2 and GABRA5) showed significant loss-of-function effects with reduced current amplitudes in four of seven tested variants compared with wild-type receptors.

INTERPRETATION

Functionally relevant variants in genes encoding GABA_A receptor subunits constitute a significant risk factor for genetic generalised epilepsy. Examination of the role of specific gene groups and pathways can disentangle the complex genetic architecture of genetic generalised epilepsy.

FUNDING

EuroEPINOMICS (European Science Foundation through national funding organisations), Epicure and EpiPGX (Sixth Framework Programme and Seventh Framework Programme of the European Commission), Research Unit FOR2715 (German Research Foundation and Luxembourg National Research Fund).

The impact of nonadherence to antiseizure drugs on seizure outcomes in an animal model of epilepsy

OBJECTIVE

Nonadherence to prescribed dosing regimens is a significant problem in the treatment of pediatric and adult chronic epilepsy, and can result in severe consequences to patient outcomes. In this first-of-kind preclinical study, the impact of nonadherence on seizure control was studied by simulating human patterns of nonadherence in an animal epilepsy model.

METHODS

In study 1, three different patterns of nonadherence were modeled in newly diagnosed epileptic rats treated with carbamazepine: perfect adherence (100% of pellets contained carbamazepine), variable nonadherence (50% of pellets contained carbamazepine with different dosing patterns between animals), and complete nonadherence (0% of pellets contained carbamazepine). In study 2, a cohort of newly diagnosed epileptic rats were subjected to a "drug holiday" nonadherence paradigm, that is, a 2-week on (100%), 2-week off (0%), and 2-week on (100%) carbamazepine paradigm.

RESULTS

In the first experiment, the 100% (0.3 ± 0.2 SD convulsive seizures per day) adherent cohort demonstrated better seizure control than either the 0% (1.1 ± 0.8 SD) or 50% (0.8 ± 0.6 SD) adherent cohorts, which had similar levels of seizure control. In the second study, poor seizure control was exhibited during the second 2 weeks; that is, the drug holiday epoch; however, this did not negatively affect restoration of seizure control upon reinstatement of CBZ.

SIGNIFICANCE

The results from this pilot investigation suggest that nonadherence to carbamazepine is associated with significant negative but reversible effects on seizure control in an animal model of epilepsy. Furthermore, these results demonstrate that animal studies of nonadherence can yield potentially important and translatable insights into the consequences of nonadherence on seizure control.

When should clinicians search for GLUT1 deficiency syndrome in childhood generalized epilepsies?

GLUT1 deficiency (GLUT1D) has recently been identified as an important cause of generalized epilepsies in childhood. As it is a treatable condition, it is crucial to determine which patients should be investigated.

METHODS

We analyzed SLC2A1 for mutations in a group of 93 unrelated children with generalized epilepsies. Fasting lumbar puncture was performed following the identification of a mutation. We compared our results with a systematic review of 7 publications of series of patients with generalized epilepsies screened for SLC2A1 mutations.

RESULTS

We found 2/93 (2.1%) patients with a SLC2A1 mutation. One, carrying a novel de novo deletion had epilepsy with myoclonic-atonic seizures (MAE), mild slowing of head growth, choreiform movements and developmental delay. The other, with a paternally inherited missense mutation, had childhood absence epilepsy with atypical EEG features and paroxysmal exercise-induced dyskinesia (PED) initially misdiagnosed as myoclonic seizures. Out of a total of 1110 screened patients with generalized epilepsies from 7 studies, 2.4% (29/1110) had GLUT1D. This rate was higher (5.6%) among 303 patients with early onset absence epilepsy (EOAE) from 4 studies. About 50% of GLUT1D patients had abnormal movements and 41% a family history of seizures, abnormal movements or both.

CONCLUSION

GLUT1D is most likely to be found in MAE and in EOAE. The probability of finding GLUT1D in the classical idiopathic generalized epilepsies is very low. Pointers to GLUT1D include an increase in seizures before meals, cognitive impairment, or PED which can easily be overlooked.