The Impact of Potassium Channel Gene Polymorphisms on Antiepileptic Drug Responsiveness in Arab Patients with Epilepsy

Pharmacogenetic insights into ABCB1, ABCC2, CYP1A2, and CYP2B6 variants with epilepsy susceptibility among Egyptian Children: A retrospective case-control study

BACKGROUND

Pediatric epilepsy is a complicated neuropsychiatric disorder that is characterized by recurrent seizures and unusual synchronized electrical activities within brain tissues. It has a substantial effect on the quality of life of children, thus understanding of the hereditary considerations influencing epilepsy susceptibility and the response to antiepileptic medications is crucial. This study focuses on assessing the correlation of the ABCB1, ABCC2, CYP1A2, and CYP2B6 genetic polymorphisms with the susceptibility to epileptic seizures and their contributions to antiepileptic medication throughout the course of the disease.

METHODS

This study included 134 Egyptian epileptic children, comprising 67 drug-responsive and 67 drug-resistant patients, along with 124 healthy controls matching for age, gender, and geographical district. Genotyping of the rs2032582, rs717620, rs2273697, rs762551, and rs3745274 variants was performed using the PCR technique. Statistical analyses, including haplotype, multivariate, logistic regression, and bioinformatics approaches, were conducted to evaluate the associations within the disease.

RESULTS

The ABCC2*rs717620 (T allele) revealed an increased risk of epilepsy compared to healthy controls (OR = 2.12, p-value < 0.001), with the rs717620 (C/T + T/T genotypes) showing significant differences between drug-responsive and drug-resistant patients (p-value < 0.05). Moreover, the ABCC2*rs2273697 (A allele) indicated a decreased risk of epileptic seizures compared to healthy controls (OR = 0.51, p-value = 0.033), with the rs2273697 (G/A + A/A genotypes) indicating a significant association with drug-resistant patients (OR = 0.21, p-value = 0.002). The rs717620*T/rs2273697*G haplotype was significantly correlated with an elevated risk of epileptic seizures within drug-responsive patients (OR = 2.26, p-value = 0.019). Additionally, the CYP1A2*rs762551 (A allele) represented a protective effect against epilepsy susceptibility (OR = 0.50, p-value < 0.001), with the rs762551 (G/A + A/A genotypes) disclosing a substantial association with a decreased risk of epileptic seizures among drug-resistant patients compared to drug-responsive patients (OR = 0.07, p-value < 0.001). Conversely, the ABCB1*rs2032582 (G allele) and the CYP2B6*rs3745274 (T allele) did not attain a significant difference with the epilepsy risk compared to healthy controls (p-value > 0.05).

CONCLUSIONS

The findings of our study emphasize the importance of pharmacogenetic screening in epilepsy research, particularly regarding to drug-resistant patients. The ABCC2*rs717620 variant conferred a significant correlation with elevated risk of epileptic seizures, while the ABCC2*rs2273697 and CYP1A2*rs762551 variants confirmed their contributions as protective markers against epilepsy development. Conversely, the ABCB1*rs2032582 and CYP2B6*rs3745274 alleles were not considered as independent risk factors with the course of epilepsy disease.

Review of pharmacogenetics of antiseizure medications: focusing on genetic variants of mechanistic targets

Antiseizure medications (ASMs) play a central role in seizure management, however, unpredictability in the response to treatment persists, even among patients with similar seizure manifestations and clinical backgrounds. An objective biomarker capable of reliably predicting the response to ASMs would profoundly impact epilepsy treatment. Presently, clinicians rely on a trial-and-error approach when selecting ASMs, a time-consuming process that can result in delays in receiving alternative non-pharmacological therapies such as a ketogenetic diet, epilepsy surgery, and neuromodulation therapies. Pharmacogenetic studies investigating the correlation between ASMs and genetic variants regarding their mechanistic targets offer promise in predicting the response to treatment. Sodium channel subunit genes have been extensively studied along with other ion channels and receptors as targets, however, the results have been conflicting, possibly due to methodological disparities including inconsistent definitions of drug response, variations in ASM combinations, and diversity of genetic variants/genes studied. Nonetheless, these studies underscore the potential effect of genetic variants on the mechanism of ASMs and consequently the prediction of treatment response. Recent advances in sequencing technology have led to the generation of large genetic datasets, which may be able to enhance the predictive accuracy of the response to ASMs.

The potential implication of MDR1 and NAC1 genetic polymorphisms on resistance to antiepileptic drugs among a Jordanian epileptic population: a cross-sectional study

BACKGROUND

Resistance to antiepileptic drugs (AEDs) remains one of the main challenges to neurologists. Polymorphisms of drug efflux transporters such as multidrug resistance (MDR1) gene and target sites such as the nucleus accumbens-associated 1 (NAC1) gene have been suggested to influence the responsiveness to treatment.

AIM

Evaluation of the association of MDR1 and NAC1 polymorphisms with AEDs resistance among Jordanian epileptic patients.

SUBJECTS AND METHODS

86 Jordanian epileptics were included in the study. DNA was extracted and genotyping was conducted by polymerase chain reaction followed by sequencing. Nine single nucleotide polymorphisms (SNPs) on the MDR1 gene and six SNPs on the NAC1 gene were investigated.

RESULTS

MDR1 and NAC1 polymorphisms don't seem to influence the resistance to AEDs at the genotype or allele level. However, a strong association was found between MDR1 rs2032588 (OR = 5; 95%CI = [1.3-18.8], p = 0.01) and AEDs resistance among males at the allele level. Also, data revealed an association between MDR1 rs1128503 and AEDs resistance among females at the allele level.

CONCLUSION

The data suggest that MDR1 and NAC1 polymorphisms do not influence the AEDs resistance among Jordanian epileptics. However, there is a gender-dependent association between MDR1 polymorphisms and resistance to AEDs at two SNPs (rs2032588 and rs1128503).

A Decade of Pharmacogenetic Studies in Jordan: A Systemic Review

The aim of this study was to perform a systematic overview of the pharmacogenetic studies conducted in Jordan. A structured search of Medline was conducted for articles over the last decade (January 2010-July 2020). Studies were classified by design, sample size, drug-gene combination, and the significance of the results. Thirty-two studies met the criteria for review. Most pharmacogenomic studies had a case-only design (n = 23). Only five studies included >500 participants. The total number of genetic variants in all studies was one hundred fifteen, which were found in forty genes, including dynamic (n = 27), and kinetic (n = 9) genes. The most commonly studied drugs were within the hematology and cardiology therapeutic areas and included statins, warfarin, aspirin, and clopidogrel. Most studies (n = 18) reported results with mixed p values [<0.05 and >0.05]. Pharmacogenomic research in Jordan is still in its infancy and is limited mainly to replication attempts. The need for standardization is imperative, especially in developing countries with scarce funding resources.

DNA Methylation Signature of Epileptic Encephalopathy-Related Pathogenic Genes Encoding Ion Channels in Temporal Lobe Epilepsy

Epilepsy is characterized by highly abnormal synchronous discharge of brain neurons, and ion channels are fundamental in the generation and modulation of neural excitability. Considering that abnormal methylation can either activate or repress genes, this study was designed to explore the DNA methylation signature of pathogenic genes encoding ion channels in temporal lobe epilepsy (TLE). In total, 38 TLE patients and 38 healthy controls were enrolled in the study, and genomic DNA and total protein of the lymphocytes were extracted from peripheral blood samples to assess methylation and protein levels. The DNA methylation levels of all 12 genes examined were significantly lower in the TLE group than in the control group. After false-positive correction, 83.3% (10/12) of these genes, namely, gamma-aminobutyric acid type A receptor subunit beta1 (GABRB1), gamma-aminobutyric acid type A receptor subunit beta2 (GABRB2), gamma-aminobutyric acid type A receptor subunit beta1 (GABRB3), glutamate ionotropic receptor NMDA type subunit 1 (GRIN1), glutamate ionotropic receptor NMDA type subunit 2A (GRIN2A), glutamate ionotropic receptor NMDA type subunit 2B (GRIN2B), hyperpolarization activated cyclic nucleotide gated potassium channel 1 (HCN1), potassium voltage-gated channel subfamily A member 2 (KCNA2), potassium voltage-gated channel subfamily B member 1 (KCNB1), and potassium sodium-activated channel subfamily T member 1 (KCNT1), were still differentially expressed. Among these ion channels, HCN1 and KCNA2 were selected to evaluate the effects of DNA methylation, and the levels of these proteins were inversely upregulated in the TLE group compared to the control group. As the genes identified as having differential methylation levels are involved in both excitatory and inhibitory ion channels, this study observed by binary logistic regression that hypermethylated GARAB1 was an independent risk factor for TLE, indicating that the overwhelming effect of ion channels on TLE is probably inhibitory from the perspective of DNA methylation. All these findings support the involvement of DNA methylation in TLE pathologies, but the mechanisms need to be further investigated.

Genetic Association of Epilepsy and Anti-Epileptic Drugs Treatment in Jordanian Patients

Purpose

The aim of this study was to investigate the possible effects of single-nucleotide polymorphisms (SNPs) within SLC1A1, SLC6A1, FAM131B, GPLD1, F2, GABRG2, GABRA1, and CACNG5 genes on response to anti-epileptic drugs (AEDs) and the genetic predisposition of epilepsy in Jordanian patients.

Patients and Methods

A total of 299 healthy individuals and 296 pediatric patients from the Jordanian population were recruited. Blood samples are collected, and genotyping was performed using a custom platform array analysis.

Results

The SLC1A1 rs10815018 and FAM131B rs4236482 polymorphisms found to be associated with epilepsy susceptibility. Moreover, SLC1A1 rs10815018 and GPLD1 rs1126617 polymorphisms were associated with generalized epilepsy (GE), while FAM131B rs4236482 is associated with the focal phenotype. Regarding the therapeutic response, the genetic polymorphisms of FAM131B rs4236482, GABRA1 rs2279020, and CACNG5 rs740805 are conferred poor response (resistance) to AEDs. There was no linkage of GLPD1 haplotypes to epilepsy, its subtypes, and treatment responsiveness.

Conclusion

Our findings suggested that SLC1A1, FAM131B, and GPLD1 polymorphisms increasing the risk of generating epilepsy, while FAM131B, GABRA1, and CACNG5 variants may play a role in predicting drug response in patients with epilepsy (PWE).

Genetic Analysis of Pharmacogenomic VIP Variants of ABCB1, VDR and TPMT Genes in an Ethnically Isolated Population from the North Caucasus Living in Jordan

Background:

Differences in individual responses to the same medications remarkably differ among populations. A number of genes that play integral roles in drug responses have been designated as very important pharmacogenes (VIP), as they are responsible for differences in drug safety, efficacy, and adverse drug reactions among certain ethnic groups. Identifying the polymorphic distribution of VIP in a range of ethnic groups will be conducive to population-based personalized medicine.

Objective:

The aim of the current study is to identify the polymorphic distribution of VIP regarding the Chechen minority group from Jordan and compare their allele frequencies with other populations.

Methods:

A total of 131 unrelated Chechen individuals from Jordan were randomly recruited for blood collection. Identification of allelic and genotypic frequencies of eleven VIP variants within the genes of interest (ABCB1, VDR and TPMT) was carried out by means of the MassARRAY®System (iPLEX GOLD).

Results:

Within ABCB1, we found that the minor allele frequencies of the rs1128503 (A: 0.43), rs2032582 (A: 0.43), rs1045642 (A: 0.43). For VDR, the minor allele frequencies of rs11568820 (T: 0.18), rs1540339 (T: 0.30), rs1544410 (T: 0.41), rs2228570 (T: 0.24), rs3782905 (C: 0.28) and rs7975232 (C: 0.45). Finally, the minor allele frequencies for the TPMT rs1142345 and rs1800460 polymorphisms were found to be (C: 0.02) and (T: 0.01), respectively.

Conclusion:

Significant differences in allelic frequencies of eleven ABCB1, VDR and TPMT VIP variants were found between Jordanian Chechens and other populations. In our study, most populations that are similar to Chechens are those from South Asian, European (Finnish) and European, including: Utah residents with Northern and Western European ancestry, Toscani in Italia, Mexican ancestry in Los Angeles and Circassian from Jordan. The level of similarity between Chechens and those populations means that they might have shared high levels of gene flow in the past. The results obtained in this study will contribute to the worldwide pharmacogenomic databases and provide valuable information for future studies and better individualized treatments.

Genetic variations associated with pharmacoresistant epilepsy (Review)

Epilepsy is a common, serious neurological disorder worldwide. Although this disease can be successfully treated in most cases, not all patients respond favorably to medical treatments, which can lead to pharmacoresistant epilepsy. Drug-resistant epilepsy can be caused by a number of mechanisms that may involve environmental and genetic factors, as well as disease- and drug-related factors. In recent years, numerous studies have demonstrated that genetic variation is involved in the drug resistance of epilepsy, especially genetic variations found in drug resistance-related genes, including the voltage-dependent sodium and potassium channels genes, and the metabolizer of endogenous and xenobiotic substances genes. The present review aimed to highlight the genetic variants that are involved in the regulation of drug resistance in epilepsy; a comprehensive understanding of the role of genetic variation in drug resistance will help us develop improved strategies to regulate drug resistance efficiently and determine the pathophysiological processes that underlie this common human neurological disease.

Pharmacogenomic landscape of VIP genetic variants in Jordanian Arabs and comparison with worldwide populations

The pharmacogenomics has lately become a focal field of research that investigates the influence of genetic variations of drug-metabolizing enzymes and their receptors and downstream proteins on the interindividual variability in response to medications and adverse drug reactions. Therefore, it is significantly important to study and analyze the variations in drug response between different ethnic groups and populations. The current study aimed to detect the distribution of the genotype and allele frequencies in several very important pharmacogenetic (VIP) gene polymorphisms in the Jordanian population of Arab descent. This study involved 500 unrelated Jordanian individuals of Arab descent. A total of 65 VIP variants located within 33 candidate genes were randomly selected from the PharmGKB database and genotyped using the MassARRAY (iPLEX GOLD) system. The chi-square test was used to evaluate the significant differences of minor allele and genotype frequencies between the Jordanian and other populations including CHE, ASW, CEU, CHB, CDX, GIH, GBR, JPT, LWK, MXL, TSI, YRI, CAR, and ACB. This study revealed six variants were not in Hardy Weinberg equilibrium (HWE) (P-value > 0.05) and ten SNPs showed monomorphic features. Most of the remaining forty-nine variant frequencies were significantly different from the compared ethnic groups (P-value < 0.05). The results of this study may be helpful to develop safer treatment by applying the concept of personalized medicine based on the profile of VIP pharmacogene variants of the Jordanian population of Arab descent.

Genetic Polymorphisms of Pharmacogenes among the Genetically Isolated Circassian Subpopulation from Jordan

Several genetic variants have been identified that cause variation among different populations and even within individuals of a similar descent. This leads to interindividual variations in the optimal dose of the drug that is required to sustain the treatment efficiency. In this study, 56 single nucleotide polymorphisms (SNPs) within several pharmacogenes were analyzed in 128 unrelated subjects from a genetically isolated group of Circassian people living in Jordan. We also compared these variant distributions to other ethnic groups that are available at two databases (Genome 1000 and eXAC). Our results revealed that the distribution of allele frequencies within genes among Circassians in Jordan showed similarities and disparities when compared to other populations. This study provides a powerful base for clinically relevant SNPs to enhance medical research and future pharmacogenomic studies. Rare variants detected in isolated populations can significantly guide to novel loci involved in the development of clinically relevant traits.

Genetic polymorphisms of CYP3A5, CHRM2, and ZNF498 and their association with epilepsy susceptibility: a pharmacogenetic and case-control study

Background

A total of 50 million persons were diagnosed worldwide with epilepsy. One-third of them are experiencing debilitating seizures despite optimum anti-epileptic drugs (AEDs) treatment. Several studies have suggested that CYP3A5, CHRM2, and ZNF498 influence the pharmacokinetics of AEDs. Therefore, the severity of the disease as well as the degree of response to the AEDs could be affected by the genetic polymorphisms within these genes.

Objectives

In this study, we assessed the effect of certain single nucleotide polymorphisms (SNPs) within CYP3A5, CHRM2, and ZNF498 genes on the susceptibility to develop epilepsy and the responsiveness to AEDs treatment.

Methods

A case-control and pharmacogenetic study was conducted on samples of 299 healthy individuals in addition to 296 epileptic patients. Genotypic, allelic, and clinical data association were performed for the selected polymorphisms within the (rs324649, rs420817, rs15524, and rs1859690) in the Jordanian population.

Results

The analysis revealed no significant association of the investigated SNPs with epilepsy in general, partial and generalized epilepsy as well as drug responsiveness. CYP3A5 and ZNF498 were associated with family history (P=0.003 and P=0.002, respectively) and the classification of epilepsy for the ZNF498 variant (P=0.009). On the other hand, CHRM2 was not linked to either disease severity or treatment responsiveness.

Conclusion

Our results failed to confirm the association of CYP3A5, ZNF498, and CHRM2 variants with either disease development or treatment response. Clinical pharmacogenetic studies may contribute to treatment personalization, appropriate drug dose selection, minimizing drug adverse reactions, increasing drug efficacy, and reducing the costive burdens.

Efficacy of antiepileptic drugs in the era of pharmacogenomics: A focus on childhood

BACKGROUND

In recent years advances in the field of pharmacogenomics have expanded the concept for more individualized treatments. Our aim is to provide literature data about the relationship between genetic polymorphisms and efficacy of antiepileptic drugs in children.

METHODS

Pubmed was used as the main medical database source. Only original research papers were considered. No year-of-publication restriction was placed. Quality of evidence was assessed according to American Academy of Neurology guidelines.

RESULTS

A total of 12 cross-sectional and case-control studies fulfilled our selection criteria. ABCB1 gene was associated with drug responsiveness in 2 out of 6 studies and ABCC2 gene in 1 out of 1 studies. SCN1A gene was also associated with seizure control in 4 out of 5 studies. Cytochrome P450 genes were found to significantly affect drug responsiveness in 2 out of 4 studies, while polymorphisms of uridinediphosphateglucuronosyltransferaseUGT2B7 gene predisposed to drug-resistance in 1 out of 2 studies.

CONCLUSION

Variability in genes coding for sodium channels, drug transporters and cytochrome P450 enzymes can have a significant impact on response to antiepileptic drugs. Larger prospective studies with better stratification of samples are needed to shed light on these associations.

Effects of MTHFR and ABCC2 gene polymorphisms on antiepileptic drug responsiveness in Jordanian epileptic patients

Background

Epilepsy is one of the most common neurological diseases with unclear etiology where its genetic background and treatment regime still need further exploration.

Objectives

This study designed to evaluate the pharmacogenomics of MTHFR and ABCC2 genes, and their association with epilepsy susceptibility among Jordanian population.

Methods

A case-control study was conducted on Jordanian cohort of 296 epileptic patients and 299 healthy individuals. Custom platform array was used to genotype the genetic polymorphisms within MTHFR (rs1801133) and ABCC2 (rs717620, rs3740066, rs2273697) genes.

Results

This study revealed a significant genetic association of MTHFR rs1801133 polymorphism with susceptibility to generalized in general and generalized tonic-clonic epilepsy (GTCE)(p=0.018 and 0.01, respectively). Regarding ABCC2 gene, rs717620 was of linkage with generalized and GTCE subtypes (p=0.045 and 0.048, respectively), while rs717620 was associated with poor responder patients (p=0.036) with no linkage of the ABCC2 haplotypes.

Conclusions

MTHFR and ABCC2 polymorphisms showed an association with either epilepsy types in general or subtypes and treatment response among Jordanian population. This study also suggested that these gene polymorphisms have an important role in epilepsy development and drug effectiveness and could be of a great impact in the era of epilepsy diagnosis and treatment.