The clinical spectrum of familial and sporadic idiopathic generalized epilepsy

Gene-gene interaction network analysis indicates CNTN2 is a candidate gene for idiopathic generalized epilepsy

Twin and family studies have established the genetic contribution to idiopathic generalized epilepsy (IGE). The genetic architecture of IGE is generally complex and heterogeneous, and the majority of the genetic burden in IGE remains unsolved. We hypothesize that gene-gene interactions contribute to the complex inheritance of IGE. CNTN2 (OMIM* 615,400) variants have been identified in cases with familial adult myoclonic epilepsy and other epilepsies. To explore the gene-gene interaction network in IGE, we took the CNTN2 gene as an example and investigated its co-occurrent genetic variants in IGE cases. We performed whole-exome sequencing in 114 unrelated IGE cases and 296 healthy controls. Variants were qualified with sequencing quality, minor allele frequency, in silico prediction, genetic phenotype, and recurrent case numbers. The STRING_TOP25 gene interaction network analysis was introduced with the bait gene CNTN2 (denoted as A). The gene-gene interaction pair mode was presumed to be A + c, A + d, A + e, with a leading gene A, or A + B + f, A + B + g, A + B + h, with a double-gene A + B, or other combinations. We compared the number of gene interaction pairs between the case and control groups. We identified three pairs in the case group, CNTN2 + PTPN18, CNTN2 + CNTN1 + ANK2 + ANK3 + SNTG2, and CNTN2 + PTPRZ1, while we did not discover any pairs in the control group. The number of gene interaction pairs in the case group was much more than in the control group (p = 0.021). Taking together the genetic bioinformatics, reported epilepsy cases, and statistical evidence in the study, we supposed CNTN2 as a candidate pathogenic gene for IGE. The gene interaction network analysis might help screen candidate genes for IGE or other complex genetic disorders.

Drug resistance in idiopathic generalized epilepsies: Evidence and concepts

Although approximately 10%-15% of patients with idiopathic generalized epilepsy (IGE)/genetic generalized epilepsy remain drug-resistant, there is no consensus or established concept regarding the underlying mechanisms and prevalence. This review summarizes the recent data and the current hypotheses on mechanisms that may contribute to drug-resistant IGE. A literature search was conducted in PubMed and Embase for studies on mechanisms of drug resistance published since 1980. The literature shows neither consensus on the definition nor a widely accepted model to explain drug resistance in IGE or one of its subsyndromes. Large-scale genetic studies have failed to identify distinct genetic causes or affected genes involved in pharmacokinetics. We found clinical and experimental evidence in support of four hypotheses: (1) "network hypothesis"-the degree of drug resistance in IGE reflects the severity of cortical network alterations, (2) "minor focal lesion in a predisposed brain hypothesis"-minor cortical lesions are important for drug resistance, (3) "interneuron hypothesis"-impaired functioning of γ-aminobutyric acidergic interneurons contributes to drug resistance, and (4) "changes in drug kinetics"-genetically impaired kinetics of antiseizure medication (ASM) reduce the effectiveness of available ASMs. In summary, the exact definition and cause of drug resistance in IGE is unknown. However, published evidence suggests four different mechanisms that may warrant further investigation.

Social outcome and psychiatric comorbidity of generalized epilepsies - A case-control study

OBJECTIVE

To investigate social outcome and psychiatric comorbidity of patients with idiopathic/genetic generalized epilepsies (IGEs) and its subtypes (epilepsy with generalized tonic-clonic seizures alone [EGTCS], juvenile absence epilepsy [JAE], and juvenile myoclonic epilepsy [JME]).

METHODS

A cohort of 402 adult patients with IGE from the Danish island Funen was matched with 4020 randomly selected geography-, age-, and sex-matched controls via the Danish Civil Registration System. Based on register data, we compared social status measured by cohabitant status, educational attainment, income, affiliation to labor market, and psychiatric comorbidity.

RESULTS

As compared to controls, patients with IGE had similar cohabitant status but fewer children (no children: 59.0% vs 50.9%), and lower educational level (primary school only: 46.0% vs 37.3%), employment rate (outside of workforce: 56.7% vs 46.5%), and income (low income: 32.6% vs 24.9%) (P < 0.001 for all comparisons). Having IGE was associated with higher a proportion of psychiatric comorbidity (IGE, 22.6%; controls, 13.0%) (P < 0.001). Seizure-free patients did not differ from controls; patients with persistent seizures had lower incomes and employment rates. In the IGE subgroup analyses, JME was associated with worse social status in all parameters studied (eg, 65.9% of JME patients were outside the workforce vs 44.5% of matched controls; P < 0.001), whereas no adverse social status was identified in patients with EGTCS and JAE.

SIGNIFICANCE

Patients with IGE in general and JME in particular have poorer social status and more psychiatric comorbidity than matched population controls without epilepsy. Poor seizure control was associated with social status and may contribute to negative socioeconomic consequences associated with IGE.

Epilepsy With Myoclonic Atonic Seizures: Why Is the Yield of Genetic Testing for a "Presumed Genetic" Epilepsy Low?

Phenotypic and Genetic Spectrum of Epilepsy With Myoclonic Atonic Seizures

Tang S, Addis L, Smith A, Topp SD, Pendziwiat M, Mei D, Parker A, Agrawal S, Hughes E, Lascelles K, Williams RE, Fallon P, Robinson R, Cross HJ, Hedderly T, Eltze C, Kerr T, Desurkar A, Hussain N, Kinali M, Bagnasco I, Vassallo G, Whitehouse W, Goyal S, Absoud M, EuroEPINOMICS-RES Consortium, Møller RS, Helbig I, Weber, YG, Marini C, Guerrini R, Simpson MA, Pal DK. Epilepsia. 2020;61(5):995-1007. doi: 10.1111/epi.16508

Objective:

We aimed to describe the extent of neurodevelopmental impairments and identify the genetic etiologies in a large cohort of patients with epilepsy with myoclonic atonic seizures (MAEs).

Methods:

We deeply phenotyped patients with MAE for epilepsy features, intellectual disability, autism spectrum disorder, and attention-deficit/hyperactivity disorder using standardized neuropsychological instruments. We performed exome analysis (whole exome sequencing) filtered on epilepsy and neuropsychiatric gene sets to identify genetic etiologies.

Results:

We analyzed 101 patients with MAE (70% male). The median age of seizure onset was 34 months (range = 6-72 months). The main seizure types were myoclonic atonic or atonic in 100%, generalized tonic-clonic in 72%, myoclonic in 69%, absence in 60%, and tonic seizures in 19% of patients. We observed intellectual disability in 62% of patients, with extremely low adaptive behavioral scores in 69%. In addition, 24% exhibited symptoms of autism and 37% exhibited attention-deficit/hyperactivity symptoms. We discovered pathogenic variants in 12 (14%) of 85 patients, including 5 previously published patients. These were pathogenic genetic variants in SYNGAP1 (n = 3), KIAA2022 (n = 2), and SLC6A1 (n = 2), as well as KCNA2, SCN2A, STX1B, KCNB1, and MECP2 (n = 1 each). We also identified 3 new candidate genes, ASH1L, CHD4, and SMARCA2 in 1 patient each.

Significance:

MAE is associated with significant neurodevelopmental impairment. MAE is genetically heterogeneous, and we identified a pathogenic genetic etiology in 14% of this cohort by exome analysis. These findings suggest that MAE is a manifestation of several etiologies rather than a discrete syndromic entity.