Association Analysis of BRD2 (RING3) and Epilepsy in a Dutch Population

A BRD's (BiRD's) eye view of BET and BRPF bromodomains in neurological diseases

Neurological disorders (NLDs) are among the top leading causes for disability worldwide. Dramatic changes in the epigenetic topography of the brain and nervous system have been found in many NLDs. Histone lysine acetylation has prevailed as one of the well characterised epigenetic modifications in these diseases. Two instrumental components of the acetylation machinery are the evolutionarily conserved Bromodomain and PHD finger containing (BRPF) and Bromo and Extra terminal domain (BET) family of proteins, also referred to as acetylation 'readers'. Several reasons, including their distinct mechanisms of modulation of gene expression and their property of being highly tractable small molecule targets, have increased their translational relevance. Thus, compounds which demonstrated promising results in targeting these proteins have advanced to clinical trials. They have been established as key role players in pathologies of cancer, cardiac diseases, renal diseases and rheumatic diseases. In addition, studies implicating the role of these bromodomains in NLDs are gaining pace. In this review, we highlight the findings of these studies, and reason for the plausible roles of all BET and BRPF members in NLDs. A comprehensive understanding of their multifaceted functions would be radical in the development of therapeutic interventions.

Association of the carriage of BRD2 rs206787 and rs516535 and GJD2 rs3743123 polymorphisms with juvenile myoclonic epilepsy in Caucasian patients of Siberia

In recent years, the genetics of juvenile myoclonic epilepsy (JME) has been actively studied; the association of JME with the carriage of polymorphic allelic variants of the BRD2 (EJM3 locus) and GJD2 (EJM2 locus) genes has been established. Objective: to establish risk factors for JME in terms of a genetic predisposition; specifically, polymorphic allelic variants rs206787 and rs516535 in the BRD2 gene and rs3743123 in the GJD2 gene. Patients and methods: Examinations were made in 79 patients with JME and in 150 healthy volunteers, who were Caucasian and resided in the Siberian Federal District (SFD) and underwent determination of the carriage of single nucleotide polymorphisms (SNPs) rs206787 and rs516535 in the BRD2 gene and rs3743123 in the GJD2 gene by real-time polymerase chain reaction. Results and discussion. In 2003, American scientists from New York showed that the alleles associated with the development of JME with an autosomal recessive inheritance pattern might be located in the BRD2 gene. Patients with JME are assumed to have an autosomal dominant inheritance pattern of mutations in the BRD2 gene. British scientists revealed that different populations were found to have an association of SNP rs3918149 and no relationship of BRD2 rs206787 to the development of JME in Caucasians, as well as ascertained local linkage disequilibrium in the BRD2 gene. Our investigation has established complete linkage disequilibrium between the loci in patients with JME and in healthy individuals and no association of the carriage of SNPs rs206787 and rs516535 in the BRD2 gene with the development of JME in the patients residing in the SFD (p >0.05). German scientists studied the impact of SNP in the BRD2 gene on a predisposition to a photoparoxysmal response in patients with JME/genetic generalized epilepsy. Our investigation has indicated the association of the carriage of TT/TT haplotype for SNP rs206787 and rs516535 in the BRD2 gene with a photoparoxysmal response in patients with JME (odds ratio (OR), 3.6; 95% confidence interval (CI), 1.37–9.48; p=0.02). We have confirmed that in the studied sample, the carriage of the T allele in the GJD2 gene (rs3743123) in the homozygous form is associated with the development of JME in Caucasian patients residing in the SFD and is a risk factor for JME (OR, 2.66; 95% CI, 1.24–5.74; p=0.04). The clinically significant association of this SNP in the GJD2 gene with the development of JME had been also previously demonstrated in two independent studies conducted in the European populations in the UK and Germany. There is a rise in the proportion of homozygotes in JME patients versus the control group, suggesting that the 588T allele under consideration increases the risk for JME in the homozygous state in the autosomal recessive inheritance pattern. Conclusion. The findings suggest that it is necessary to genotype Caucasian patients with JME, who reside in Siberia, for determination of the carriage of the TT/TT haplotype in terms of the investigated SNPs in the BRD2 gene (EJM 3 locus) and the carriage the T allele (rs3743123) in the GJD2 gene via a personalized approach to predicting the course of JME, as well as for identification of persons at risk for JME in the families having a history of this disease.

Genetic susceptibility in Juvenile Myoclonic Epilepsy: Systematic review of genetic association studies

BACKGROUND

Several genetic association investigations have been performed over the last three decades to identify variants underlying Juvenile Myoclonic Epilepsy (JME). Here, we evaluate the accumulating findings and provide an updated perspective of these studies.

METHODOLOGY

A systematic literature search was conducted using the PubMed, Embase, Scopus, Lilacs, epiGAD, Google Scholar and Sigle up to February 12, 2016. The quality of the included studies was assessed by a score and classified as low and high quality. Beyond outcome measures, information was extracted on the setting for each study, characteristics of population samples and polymorphisms.

RESULTS

Fifty studies met eligibility criteria and were used for data extraction. With a single exception, all studies used a candidate gene approach, providing data on 229 polymorphisms in or near 55 different genes. Of variants investigating in independent data sets, only rs2029461 SNP in GRM4, rs3743123 in CX36 and rs3918149 in BRD2 showed a significant association with JME in at least two different background populations. The lack of consistent associations might be due to variations in experimental design and/or limitations of the approach.

CONCLUSIONS

Thus, despite intense research evidence established, specific genetic variants in JME susceptibility remain inconclusive. We discussed several issues that may compromise the quality of the results, including methodological bias, endophenotype and potential involvement of epigenetic factors.

PROSPERO REGISTRATION NUMBER

CRD42016036063.

Epi4K: gene discovery in 4,000 genomes

A major challenge in epilepsy research is to unravel the complex genetic mechanisms underlying both common and rare forms of epilepsy, as well as the genetic determinants of response to treatment. To accelerate progress in this area, the National Institute of Neurological Disorders and Stroke (NINDS) recently offered funding for the creation of a “Center without Walls” to focus on the genetics of human epilepsy. This article describes Epi4K, the collaborative study supported through this grant mechanism and having the aim of analyzing the genomes of a minimum 4,000 subjects with highly selected and well-characterized epilepsy.

GABAergic neuron deficit as an idiopathic generalized epilepsy mechanism: the role of BRD2 haploinsufficiency in juvenile myoclonic epilepsy

Idiopathic generalized epilepsy (IGE) syndromes represent about 30% of all epilepsies. They have strong, but elusive, genetic components and sex-specific seizure expression. Multiple linkage and population association studies have connected the bromodomain-containing gene BRD2 to forms of IGE. In mice, a null mutation at the homologous Brd2 locus results in embryonic lethality while heterozygous Brd2+/− mice are viable and overtly normal. However, using the flurothyl model, we now show, that compared to the Brd2+/+ littermates, Brd2+/− males have a decreased clonic, and females a decreased tonic-clonic, seizure threshold. Additionally, long-term EEG/video recordings captured spontaneous seizures in three out of five recorded Brd2+/− female mice. Anatomical analysis of specific regions of the brain further revealed significant differences in Brd2+/− vs +/+ mice. Specifically, there were decreases in the numbers of GABAergic (parvalbumin- or GAD67-immunopositive) neurons along the basal ganglia pathway, i.e., in the neocortex and striatum of Brd2+/− mice, compared to Brd2+/+ mice. There were also fewer GABAergic neurons in the substantia nigra reticulata (SNR), yet there was a minor, possibly compensatory increase in the GABA producing enzyme GAD67 in these SNR cells. Further, GAD67 expression in the superior colliculus and ventral medial thalamic nucleus, the main SNR outputs, was significantly decreased in Brd2+/− mice, further supporting GABA downregulation. Our data show that the non-channel-encoding, developmentally critical Brd2 gene is associated with i) sex-specific increases in seizure susceptibility, ii) the development of spontaneous seizures, and iii) seizure-related anatomical changes in the GABA system, supporting BRD2's involvement in human IGE.

Genetic linkage study of an autosomal recessive form of juvenile myoclonic epilepsy in a consanguineous Tunisian family

Juvenile myoclonic epilepsy (JME) is the most common idiopathic generalized epilepsies (IGEs), affecting 12-30% of all epilepsies in medical centers. To date genetic linkage studies have revealed putative loci on different chromosomes, but these findings are still inconclusive about which gene precisely is responsible for the disease. Here, we report the genetic and clinical analysis of a (JME) consanguineous Tunisian family with four affected children out of eight. A genome-wide search was carried out by using the Affymetrix GeneChip Mapping 500K NspI chip. Pairewise logarithm of the odds (LOD) scores were calculated with MERLIN (1.1) assuming an autosomal recessive model, and a complementary homozygous mapping analysis was performed with AutoSNPa software. The genome-wide parametric linkage analysis showed suggestive linkage to chromosome 2q. Interactive visual analysis of SNP data using AutoSNPa revealed two large regions of shared homozygosity by descent on 2q23.3 and on 2q24.1. We decided to sequence the exons of the two genes coding for such proteins located in 2q23.3, CACNB4 and 2q24.1, KCNJ3. No nucleotide variation--comprising the previously reported mutations--was detected.

Role of GRM4 in idiopathic generalized epilepsies analysed by genetic association and sequence analysis

BACKGROUND

GRM4 encoding the group III metabotropic glutamate receptor 4 (mGluR4), is located on the chromosomal segment 6p21.3 where tentative susceptibility loci for Juvenile Myoclonic Epilepsy (JME) and Photoparoxysmal Response (PPR) have been mapped. The present candidate gene study examined if variation in GRM4 confers susceptibility to IGE.

PATIENTS AND METHODS

The case-control association sample included 564 unrelated IGE patients and 733 population controls of German descent. Association analysis was carried out for 17 single nucleotide polymorphisms (SNPs) covering the genomic GRM4 sequence for all IGE patients as well as for two common IGE subsyndromes [Juvenile Myoclonic Epilepsy (JME, n=215) and Childhood Absence Epilepsy (CAE, n=175)]. Sequence analysis was performed in 85 IGE and 42 PPR cases and 44 controls.

RESULTS

Nominally significant associations were detected between IGE and seven GRM4 SNPs (with P-values ranging from 0.037 to 0.0036), between JME and five SNPs (P=0.042-0.0106), and between CAE and two SNPs (P=0.0466-0.0021). Four novel SNPs were identified by sequence analysis.

CONCLUSIONS

Our association findings support the hypothesis that GRM4 sequence variants might confer low-risk effects to the etiology of IGE. A minor pathogenetic contribution of the examined variants is possible. These exploratory findings warrant further replication analyses.

BRD2 and TAP-1 genes and juvenile myoclonic epilepsy

Juvenile myoclonic epilepsy (JME) is a genetically determined common subtype of idiopathic generalized epilepsy. Linkage of JME to the chromosomal region 6p21.3 has been reported. An association has been previously observed between JME and the positional candidate, 6p21.3 linked, BRD2. Another candidate in this region is the TAP-1 gene encoding the Transporter Associated with Antigen Processing. The aim of the present study is to determine whether these two genes modulate the vulnerability to JME. While no difference was observed in the allele and genotype frequencies of BRD2 between JME and controls, an association was found between a TAP-1 haplotype and JME, suggesting that this gene may be another 6p21.3 linked vulnerability factor to JME.