Genetic biomarkers in epilepsy

Seizure-suppressor genes: can they help spearhead the discovery of novel therapeutic targets for epilepsy?

INTRODUCTION

Epilepsies are disorders of neuronal excitability characterized by spontaneously recurrent focal and generalized seizures, some of which result from genetic mutations. Despite the availability of antiseizure medications, pharmaco-resistant epilepsy is seen in about 23% of epileptic patients worldwide. Therefore, there is an urgent need to develop novel therapeutic strategies for epilepsies. Several epilepsy-associated genes have been found in humans. Seizure susceptibility can also be induced in Drosophila mutants, some showing features resembling human epilepsies. Interestingly, several second-site mutation gene products have been found to suppress seizure susceptibility in the seizure genetic model Drosophila. Thus, these so-called 'seizure-suppressor' gene variants may lead to developing a novel class of antiseizure medications.

AREA COVERED

This review evaluates the potential therapeutic of seizure-suppressor gene variants.

EXPERT OPINION

Studies on epilepsy-associated genes have allowed analyses of mutations linked to human epilepsy by reproducing these mutations in Drosophila using reverse genetics to generate potential antiseizure therapeutics. As a result, about fifteen seizure-suppressor gene mutants have been identified. Furthermore, some of these epilepsy gene mutations affect ligand-and voltage-gated ion channels. Therefore, a better understanding of the antiseizure activity of seizure-suppressor genes is essential in advancing gene therapy and precision medicine for epilepsy.

The importance of discriminative power rather than significance when evaluating potential clinical biomarkers in epilepsy research

OBJECTIVE

The quest for epilepsy biomarkers is on the rise. Variables with statistically significant group-level differences are often misinterpreted as biomarkers with sufficient discriminative power. This study aimed to demonstrate the relationship between significant group-level differences and a variable's power to discriminate between individuals.

METHODS

We simulated normal-distributed datasets from hypothetical populations with varying sample sizes (25-800), effect sizes (Cohen's d: .25-2.50), and variability (standard deviation: 10-35) to assess the impact of these parameters on significance and discriminative power. The simulation data were illustrated by assessing the discriminative power of a potential real-case biomarker-the EEG beta band power-to diagnose generalized epilepsy, using data from 66 children with generalized epilepsy and 385 controls. Additionally, we evaluated recently reported epilepsy biomarkers by comparing their effect sizes to our simulation-derived effect size criterion.

RESULTS

Group size affects significance but not discriminative power. Discriminative power is much more related to variability and effect size. Our real data example supported these simulation results by demonstrating that group-level significance does not translate, one to one, into discriminative power. Although we found a significant difference in the beta band power between children with and without epilepsy, the discriminative power was poor due to a small effect size. A Cohen's d of at least 1.25 is required to reach good discriminative power in univariable prediction modeling. Slightly over 60% of the biomarkers in our literature search met this criterion.

SIGNIFICANCE

Rather than statistical significance of group-level differences, effect size should be used as an indicator of a variable's biomarker potential. The minimal required effects size for individual biomarkers-a Cohen's d of 1.25-is large. This calls for multivariable approaches, in which combining multiple variables with smaller effect sizes could increase the overall effect size and discriminative power.

EEG biomarker candidates for the identification of epilepsy

Electroencephalography (EEG) is one of the main pillars used for the diagnosis and study of epilepsy, readily employed after a possible first seizure has occurred. The most established biomarker of epilepsy, in case seizures are not recorded, are interictal epileptiform discharges (IEDs). In clinical practice, however, IEDs are not always present and the EEG may appear completely normal despite an underlying epileptic disorder, often leading to difficulties in the diagnosis of the disease. Thus, finding other biomarkers that reliably predict whether an individual suffers from epilepsy even in the absence of evident epileptic activity would be extremely helpful, since they could allow shortening the period of diagnostic uncertainty and consequently decreasing the risk of seizure. To date only a few EEG features other than IEDs seem to be promising candidates able to distinguish between epilepsy, i.e. > 60 % risk of recurrent seizures, or other (pathological) conditions. The aim of this narrative review is to provide an overview of the EEG-based biomarker candidates for epilepsy and the techniques employed for their identification.

Aberrant Expression of Serum MicroRNA-153 and -199a in Generalized Epilepsy and its Correlation with Drug Resistance

Background:

Epilepsy is one of the common neurological disorders affecting approximately 50 million people worldwide. Despite the recent introduction of new antiepileptic drugs, about one-third of patients with epilepsy have seizures refractory to pharmacotherapy. Early recognition of patients with drug-resistant epilepsy may help direct these patients to appropriate nonpharmacological treatment.

Purpose:

The possible use of serum microRNAs (miRNAs) as noninvasive biomarkers has been explored in various brain diseases, including epilepsy. In this study, we are aiming at analyzing the expression levels of circulating miRNA-153 and miRNA-199a in patients with generalized epilepsy and their correlation with drug resistance.

Methods:

Our study comprised 40 patients with generalized epilepsy and 20 healthy controls. 22 patients were drug-resistant and 18 patients were drug-responsive. The expression levels of miRNA-153 and -199a in serum were analyzed using quantitative real-time polymerase chain reaction. Data analysis was done by IBM SPSS Statistics 20.0.

Results:

The expression of miRNA-153 and -199a in serum was significantly downregulated in patients with generalized epilepsy compared with that of the healthy control ( P < .001). Combined expression level of serum miRNA-153 and -199a had a sensitivity of 85% and a specificity of 90% in the diagnosis of generalized epilepsy. Furthermore, the expression levels of miRNA-153 and -199a were significantly decreased in drug-resistant patients compared to the drug-responsive group, and the combination of both markers gave the best results in differentiating between the two groups.

Conclusion:

We suggest that serum miRNAs-153 and -199a expression levels could be potential noninvasive biomarkers supporting the diagnosis of generalized epilepsy. Moreover, they could be used for the early detection of refractory generalized epilepsy.

Assessing the role of rare genetic variants in drug-resistant, non-lesional focal epilepsy

OBJECTIVE

Resistance to antiseizure medications (ASMs) is one of the major concerns in the treatment of epilepsy. Despite the increasing number of ASMs available, the proportion of individuals with drug-resistant epilepsy remains unchanged. In this study, we aimed to investigate the role of rare genetic variants in ASM resistance.

METHODS

We performed exome sequencing of 1,128 individuals with non-familial non-acquired focal epilepsy (NAFE) (762 non-responders, 366 responders) and were provided with 1,734 healthy controls. We undertook replication in a cohort of 350 individuals with NAFE (165 non-responders, 185 responders). We performed gene-based and gene-set-based kernel association tests to investigate potential enrichment of rare variants in relation to drug response status and to risk for NAFE.

RESULTS

We found no gene or gene set that reached genome-wide significance. Yet, we identified several prospective candidate genes - among them DEPDC5, which showed a potential association with resistance to ASMs. We found some evidence for an enrichment of truncating variants in dominant familial NAFE genes in our cohort of non-familial NAFE and in association with drug-resistant NAFE.

INTERPRETATION

Our study identifies potential candidate genes for ASM resistance. Our results corroborate the role of rare variants for non-familial NAFE and imply their involvement in drug-resistant epilepsy. Future large-scale genetic research studies are needed to substantiate these findings.

[Decision support systems, assistance systems and telemedicine in epileptology]

Hintergrund

Die wissenschaftlichen Erkenntnisse über Epilepsien und deren klinische Implikationen nehmen rasant zu. Für Nichtexperten stellt sich die zunehmende Herausforderung, den Überblick hierüber zu bewahren. Hier setzen Clinical-decision-support-Systeme (CDSS) an, indem sie standard- und expertengetriggertes Wissen zur Diagnostik und Therapie individualisiert und automatisiert liefern. Zudem sind Medizin-Apps und telemedizinische Verfahren zur Diagnostik und Therapie sowie Assistenzsysteme zur Anfallsdetektion bei Epilepsien verfügbar.

Ziel der Arbeit

Es soll ein Überblick über die aktuellen Entwicklungen und Anwendungsmöglichkeiten verfügbarer tele-epileptologischer Methoden gegeben werden.

Material und Methoden

Auf der Basis persönlicher Kenntnis und eines Literaturreviews werden epilepsiespezifische CDSS, Medizin-Apps, Assistenzsysteme sowie telemedizinische Anwendungen charakterisiert und deren klinische Einsatzmöglichkeiten dargestellt.

Ergebnisse und Diskussion

Personen mit Epilepsie könnten aufgrund des chronischen Verlaufs und der Komplexität der Erkrankung und ihrer Folgen von CDSS profitieren. Es erscheint wünschenswert, dass epilepsiespezifische CDSS sowohl für die Behandelnden als auch für Patienten nutzbar werden. Apps für Menschen mit Epilepsie dienen derzeit meist der Verlaufsdokumentation von Anfallsfrequenz, Medikamentencompliance und Nebenwirkungen. Gegenwärtige Anfallsdetektionssysteme erkennen vor allem generalisiert tonisch-klonische Anfälle (GTKA). Ein klinischer Nutzen ist noch nicht hinreichend belegt, erscheint aber wahrscheinlich, insbesondere da GTKA mit dem Risiko eines plötzlichen Todes von Epilepsiepatienten assoziiert sind und Interventionen als wirksam gelten.

Epilepsy-Related Voltage-Gated Sodium Channelopathies: A Review

Epilepsy is a disease characterized by abnormal brain activity and a predisposition to generate epileptic seizures, leading to neurobiological, cognitive, psychological, social, and economic impacts for the patient. There are several known causes for epilepsy; one of them is the malfunction of ion channels, resulting from mutations. Voltage-gated sodium channels (NaV) play an essential role in the generation and propagation of action potential, and malfunction caused by mutations can induce irregular neuronal activity. That said, several genetic variations in NaV channels have been described and associated with epilepsy. These mutations can affect channel kinetics, modifying channel activation, inactivation, recovery from inactivation, and/or the current window. Among the NaV subtypes related to epilepsy, NaV1.1 is doubtless the most relevant, with more than 1500 mutations described. Truncation and missense mutations are the most observed alterations. In addition, several studies have already related mutated NaV channels with the electrophysiological functioning of the channel, aiming to correlate with the epilepsy phenotype. The present review provides an overview of studies on epilepsy-associated mutated human NaV1.1, NaV1.2, NaV1.3, NaV1.6, and NaV1.7.

Individualizing Treatment Approaches for Epileptic Patients with Glucose Transporter Type1 (GLUT-1) Deficiency

Monogenic and polygenic mutations are important contributors in patients suffering from epilepsy, including metabolic epilepsies which are inborn errors of metabolism with a good respond to specific dietetic treatments. Heterozygous variation in solute carrier family 2, facilitated glucose transporter member 1 (SLC2A1) and mutations of the GLUT1/SLC2A2 gene results in the failure of glucose transport, which is related with a glucose type-1 transporter (GLUT1) deficiency syndrome (GLUT1DS). GLUT1 deficiency syndrome is a treatable disorder of glucose transport into the brain caused by a variety of mutations in the SLC2A1 gene which are the cause of different neurological disorders also with different types of epilepsy and related clinical phenotypes. Since patients continue to experience seizures due to a pharmacoresistance, an early clinical diagnosis associated with specific genetic testing in SLC2A1 pathogenic variants in clinical phenotypes could predict pure drug response and might improve safety and efficacy of treatment with the initiation of an alternative energy source including ketogenic or analog diets in such patients providing individualized strategy approaches.

Association between SCN1A gene polymorphisms and drug resistant epilepsy in pediatric patients

PURPOSE

"Single Nucleotide Polymorphisms (SNPs)" could be an important explanation of drug resistance in epilepsy. The aim of this study was to investigate if genetic polymorphisms (SNPs) of the SCN1A gene could influence the response to anti - epileptic drugs (AED) and if they could predispose to a drug resistant epilepsy in pediatric patients.

METHODS

We investigated SNPs in exon and intronic regions of the SCN1A gene in a sample of 120 pediatric patients, in both drug-resistant and drug-responsive patients. Association between polymorphisms and refractory epilepsy were investigated by comparing SNPs in exon and intronic regions between the two groups. The genotypes of each intronic polymorphism in the drug-resistant group was analyzed. Odds ratios and confidence intervals were calculated.

RESULTS

None of the SNPs identified in exons of the SCN1A gene were associated with drug-resistance. In the intronic regions, a statistically significant difference was found in the prevalence of three polymorphisms was found between the two patient groups (rs6730344A/C, rs6732655A/T, rs10167228A/T). The analysis of the genotypes of each intronic polymorphism in the drug-resistant group revealed that the AA and AT genotypes for the rs1962842 polymorphism are associated with an increased risk of developing drug resistance compared to TT genotype.

CONCLUSION

The intronic rs6730344, rs6732655 and rs10167228 polymorphisms of the SCN1A gene are a potential risk factors for drug resistance. AA e AT genotype of the rs1962842 intronic polymorphism also emerged as a risk factor in the drug resistant group. Therefore, polymorphisms of the SCN1A gene could play a role in the response to AED in patients with drug-resistant epilepsy, with important implications for clinical practice.

Novel insights into the effect of paroxetine administration in pilocarpine‑induced chronic epileptic rats

The aim of the present study was to investigate the role of paroxetine intervention in epilepsy, and its association with the expression of serotonin transporter (SERT) and hippocampal apoptosis. Thirty adult male Sprague Dawley rats were divided into control vehicle (n=6) and epileptic (n=24) groups. Status epilepticus (SE) was induced via systemic injection of pilocarpine, and seizure activity was monitored via video electroencephalogram. The epileptic group was then randomly divided into two groups; Four weeks following SE induction, paroxetine (5 mg/kg/day; SE + paroxetine group) or normal saline (SE group) was intraperitoneally injected for 4 weeks. Brain tissue was collected to evaluate apoptosis via terminal deoxynucleotidyl transferase dUTP nick‑end labeling. SERT, B‑cell lymphoma‑2 (Bcl‑2) and brain derived neurotropic factor (BDNF) expression levels were evaluated by western blotting, and miR‑16 expression was evaluated by reverse transcription‑quantitative polymerase chain reaction. Paroxetine did not affect the mortality of the pilocarpine‑induced chronic epileptic rats. Spontaneous recurrent seizures (SSRs) were observed 7‑28 days following SE induction. The frequency and stage of the SSRs were reduced by paroxetine administration. Apoptotic cells were observed in the epileptic hippocampus. Following paroxetine intervention, the staining intensity and number of apoptotic cells were significantly decreased. Expression levels of BDNF and Bcl‑2 were lower in the SE group compared with the vehicle group. The former was not altered by paroxetine injection; however, the latter was increased. In the SE group, SERT expression was not altered in the raphe nucleus but was decreased in the hippocampus. Following paroxetine administration, SERT expression was decreased in the raphe nucleus and increased in the hippocampus. In the SE group, miR‑16 expression was decreased in the raphe nucleus and increased in the hippocampus. Following paroxetine administration, miR‑16 expression was not altered in the raphe nucleus but was reduced in the hippocampus. In conclusion, the seizures and hippocampal apoptosis observed in chronic epileptic rats were alleviated by paroxetine treatment. This effect may be associated with the reduced Bcl‑2 and BDNF expression and the modulation of SERT expression. The alterations in miR‑16 expression may provide a potential explanation for the modulation of apoptosis; however, further research is required to determine the complete underlying molecular mechanism.

Polymorphisms in ABCB1 and EPHX1 genes influence drug effectiveness in refractory epilepsy: a retrospective study

Aim: Thirty percent of epileptic patients are refractory to treatment. We investigated the association between the number of seizures in refractory epileptic patients and potential interactions between their antiepileptic medications (AEDs) and single nucleotide polymorphisms in genes ABCB1, CYP2C9 and EPHX1. Methods: Thirty-three adult patients were included and tested for genetic variations using the Neuropharmagen® test. Retrospective data on AED therapy and number of seizures during the 12 months before inclusion were extracted from clinical records. Results: Patients displaying potential single nucleotide polymorphisms × AED interactions had a median of 14.5 seizures during the previous 12 months (IQR 5.5–105.0), compared to a median of 7.0 seizures (IQR 4.0–12.0) in patients without these interactions (univariate p = 0.051, adjusted p = 0.034). Conclusion: Refractory patients carrying genetic variations potentially affecting their AED medication experienced a significantly higher number of seizures. Thus, genotyping could help to better control epilepsy in some refractory patients.

Impact of Genetic Polymorphisms of ABCB1 (MDR1, P-Glycoprotein) on Drug Disposition and Potential Clinical Implications: Update of the Literature

ATP-binding cassette transporter B1 (ABCB1; P-glycoprotein; multidrug resistance protein 1) is an adenosine triphosphate (ATP)-dependent efflux transporter located in the plasma membrane of many different cell types. Numerous structurally unrelated compounds, including drugs and environmental toxins, have been identified as substrates. ABCB1 limits the absorption of xenobiotics from the gut lumen, protects sensitive tissues (e.g. the brain, fetus and testes) from xenobiotics and is involved in biliary and renal secretion of its substrates. In recent years, a large number of polymorphisms of the ABCB1 [ATP-binding cassette, sub-family B (MDR/TAP), member 1] gene have been described. The variants 1236C>T (rs1128503, p.G412G), 2677G>T/A (rs2032582, p.A893S/T) and 3435C>T (rs1045642, p.I1145I) occur at high allele frequencies and create a common haplotype; therefore, they have been most widely studied. This review provides an overview of clinical studies published between 2002 and March 2015. In summary, the effect of ABCB1 variation on P-glycoprotein expression (messenger RNA and protein expression) and/or activity in various tissues (e.g. the liver, gut and heart) appears to be small. Although polymorphisms and haplotypes of ABCB1 have been associated with alterations in drug disposition and drug response, including adverse events with various ABCB1 substrates in different ethnic populations, the results have been majorly conflicting, with limited clinical relevance. Future research activities are warranted, considering a deep-sequencing approach, as well as well-designed clinical studies with appropriate sample sizes to elucidate the impact of rare ABCB1 variants and their potential consequences for effect sizes.