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Bromodomain-Containing Protein 2 gene in photosensitive epilepsy
Seizure 21 (2012) 646–648
Contents lists available at SciVerse ScienceDirect
Seizure journal homepage: www.elsevier.com/locate/yseiz
Short communication
Bromodomain-Containing Protein 2 gene in photosensitive epilepsy§ Ebru Nur Yavuz a, Ozkan Ozdemir b, Suzin Catal b, Nerses Bebek a,b, Ugur Ozbek b, Betul Baykan a,b,* a b
Istanbul University, Istanbul Faculty of Medicine, Department of Neurology and Istanbul University Epilepsy Center, Turkey Istanbul University, Institute of Experimental Medicine (DETAE), Department of Genetics, Turkey
A R T I C L E I N F O
A B S T R A C T
Article history: Received 1 April 2012 Received in revised form 31 May 2012 Accepted 2 June 2012
Purpose: Photosensitive epilepsy (PSE) is a form of reflex epilepsy characterized by seizures triggered by light. Genetic factors play an important role and some studies have indicated a possible role of the Bromodomain-Containing Protein 2 (BRD2) gene. Our aim was to investigate the relationship between PSE and mutations of the BRD2 gene. Methods: Fifty-four PSE patients with normal findings on neurological examination and neuro-imaging studies were included. All had a clear photoparoxysmal response in the EEG as reported by 2 experienced EEG interpreters. We investigated the BRD2 gene by denaturing high performance liquid chromatography followed by direct DNA sequencing. Results: We failed to detect any mutations of the BRD2 gene. However, several single-nucleotide polymorphisms (SNPs) were observed in the gene; three of them were novel SNPs. The comparison of the patients showing these SNP changes with the remaining patients suggested a link between carrier status and prognosis. Conclusion: Our study did not confirm the presence of the genetic variants previously found to link the BRD2 gene to the idiopathic form of photosensitive epilepsy. SNP changes of the BRD2 gene may be clinically relevant but these findings need to be verified by larger studies. ß 2012 British Epilepsy Association. Published by Elsevier Ltd. All rights reserved.
Keywords: Photosensitive epilepsy BRD2 gene Epilepsy genetics Juvenile myoclonic epilepsy Mutation Polymorphism
1. Introduction Photosensitivity is an abnormal, exaggerated response of the brain to light defined by the occurrence of spikes or spikes and waves in response to intermittent photic stimulation (IPS) in the electroencephalogram (EEG).1,2 Photosensitive epilepsy (PSE) is a heterogeneous genetic epilepsy with seizures triggered by IPS or daily light sources.1,2 Photosensitivity is frequently observed in idiopathic (genetic) generalized epilepsy (IGE) especially in its subtypes juvenile myoclonic epilepsy (JME), childhood and juvenile absence epilepsy, and also in the idiopathic photosensitive occipital lobe epilepsy (IPOE).3,4 Although PSE is commonly observed in the neurology practice, its pathophysiology has not yet been explained. Genetic factors play an important role and one study has indicated a relation with the Bromodomain-Containing Protein 2 (BRD2) gene.5 Highly
§
This study was presented in a preliminary form as a poster in the 63rd Annual American Academy of Neurology Meeting, held in Toronto on April 10–17, 2010. The study was approved by the Ethics Committee of the Istanbul Faculty of Medicine (23.5.2007-05). * Corresponding author at: Istanbul University, Istanbul Faculty of Medicine, Department of Neurology, Millet Cad, 34390 Capa, Istanbul, Turkey. Tel.: +90 212 414 2000x32598; fax: +90 212 533 4393. E-mail addresses: [email protected], [email protected] (B. Baykan).
significant linkage disequilibrium (LD) was shown between JME and a core haplotype of five single-nucleotide-polymorphism (SNP) and microsatellite markers with LD peaking in the BRD2 (RING3) gene.6 Lorenz et al. reported allelic and haplotypic associations between photoparoxysmal response (PPR) and six BRD2 polymorphisms in 187 subjects exhibiting PPR and 666 healthy controls.5 Considering the strong neurobiological association of JME with PPR, these results suggested that PPR and JME may share epileptogenic pathways, for which the BRD2 gene variations might be an underlying susceptibility factor.5 Our aim was to investigate the relationship between idiopathic PSE and the mutations or polymorphisms of the BRD2 gene in a group of Turkish patients. We also assessed whether patients with variants of BRD2 differ from patients without these variants. 2. Materials and methods We included 54 patients with idiopathic/genetic epilepsy having a clear photoparoxysmal response in at least one EEG as reported by 2 experienced interpreters. All participants had normal findings on neurological examination and neuro-imaging studies. The patients with epileptic discharges during resting EEG or during hyperventilation had at least two-fold or more increase in the epileptic discharges during IPS. All patients were followed up by the same Epilepsy Center at least for 2 years to determine the prognosis. They underwent interictal or ictal EEG studies. EEG
1059-1311/$ – see front matter ß 2012 British Epilepsy Association. Published by Elsevier Ltd. All rights reserved. http://dx.doi.org/10.1016/j.seizure.2012.06.008
E.N. Yavuz et al. / Seizure 21 (2012) 646–648
investigations were performed using a standard IPS scheme. It started eyes open for 5 s and then eyes closed for 5 s; the stimulus train was given in a screening phase with 5–10–15–20–25–30– 35 Hz as described elsewhere.4 Clinical photosensitivity was defined as the self-report of the patients stating that their seizures were induced by light during daily life (sunlight, TV, video games, patterns, etc.). All patients’ clinical and EEG files were evaluated in detail for characteristics such as sex, current age, median age at onset, triggers for seizures in daily life, seizure types and syndrome classification. An epilepsy syndrome diagnosis was made for each patient, based on the clinical and EEG features according to the International League Against Epilepsy (ILAE) classification. The patients with myoclonia as the predominant seizure type were diagnosed as juvenile myoclonic epilepsy, whereas the others having absence seizures were grouped according to the age at onset before and after 10 years, as childhood or juvenile absence epilepsy. The study was approved by the local ethics committee and all patients gave written informed consent. The remission for 2 years and relapses were also evaluated. DNA was extracted from blood samples using Qiagen DNA extraction kit. Specific primers for each exon, including exon– intron boundary sites were designed with the BRD2 sequence taken from NCBI (NM_001113182.2) database by using ‘‘primer3’’ software (http://frodo.wi.mit.edu/primer3/). After optimization stage, polymerase chain reaction (PCR) was performed for all 13 exons and PCR products were controlled with 3% agarose gel electrophoresis. Amplified PCR products were scanned through the dHPLC (denaturing high-performance liquid chromatography) system (WAVE System Model 3500 HT) in specific conditions. Denaturation patterns of all amplicons were carefully investigated and those samples having any deflection over others were confirmed by bidirectional sequencing (for both 50 and 30 strands). We used Fisher’s exact test to compare clinical findings between the group of patients who have at least one variation and the group of patients without variation. P values less than 0.05 were considered statistically significant. 3. Results There were 40 women and 14 men diagnosed with PSE and their current ages were between 12 and 63 years. The median age at onset of the seizures was 13.1 5.5 years. Fifty-two patients were diagnosed with IGE (34 with JME, 4 with childhood absence epilepsy, 10 with juvenile absence epilepsy, 4 with late-onset IGE) and the remaining two patients were diagnosed with IPOE.4 All patients had PPR in the EEG and 43 patients also reported seizures triggered by light in their daily life (TV in 16 pts, sunlight in 17, computer/video 7 pts, patterns 4 pts). The variants found after sequencing analysis are presented in Table 1. Three unknown variants were found, but none of them Table 1 Sequenced samples and variations of the BRD2 gene. Number of patientsa
Variant
Position
Aminoacid Change
2 2 2 1b 13 1b 6 1 2b
rs9276935; heterozygous rs55912052; heterozygous rs516535; heterozygous c.177C>A; heterozygous rs15912; hetero-homozygous c.2147-10A>C rs2071876; heterozygous rs3918140; heterozygous c.3053G>A
50 UTR 50 UTR Exon 3 Exon 3 Exon 6 Intron Exon 13 Exon 13 30 UTR
– – Lys > Lys Ala > Ala Leu > Leu – Ser > Ser Ser > Ser –
a b
Some patients have more than one variation. Unknown variants.
647
Table 2 Comparison of patients with and without SNP changes in the BRD2 gene.
Poor prognosis (no remission) 1st degree consanguineous marriage Family history of epilepsy JME syndrome Recorded seizure during IPS Absence seizures Generalized tonic–clonic convulsions
Group1 (n: 26)
Group2 (n: 28)
P value
8 5 16 18 8 10 22
17 5 10 16 14 13 22
0.03a Ns Ns Ns Ns Ns Ns
JME, juvenile myoclonus epilepsy; IPS, intermittent photic stimulation; ns, not significant. Group 1, patients with single nucleotide polymorphism in the BRD2 gene. Group 2, patients without SNPs in the BRD2 gene. a Fisher’s exact test.
cause any aminoacid change or splicing defect. The other variants were well-known polymorphisms. We compared the clinical and EEG features of the patients showing these SNP changes (26 cases), with the remaining patients without any SNP changes (28 patients) using the nonparametric Fisher’s exact test. We found a statistically significant association of the SNPs in the BRD2 gene with the prognosis (which is defined as seizure remission for 2 years under anti-epileptic drug therapy for 26 patients versus no remission in 28 patients, P = 0.03) as shown in Table 2. 4. Discussion Reflex seizures and epilepsies are well-known entities, which create a human model that can help with the understanding of the basic mechanisms underlying epilepsy. The increased risk of exposure to potentially ictogenic artificial light sources associated with modern life makes photosensitive epilepsy (PSE) an important issue to study.7 The chromosomal region on 6p21 has shown linkage to various IGE syndromes, particularly to JME and also PSE.8,9 The BRD2 gene, a putative nuclear transcriptional regulator from a family of genes that are expressed during development, is a good positional candidate. Pal et al. reported two JME-associated SNP variants in the BRD2 (RING3) promoter region and suggested that the BRD2 gene is EJM1, the first gene identified for JME.6 These findings also suggested that abnormalities of neural development may cause common idiopathic epilepsy.6 Recently, in a heterozygous BRD2+/ mice model, Velı´sˇek et al. reported that the non-channel-encoding, developmentally critical BRD2 gene is associated with sex-specific increases in the seizure susceptibility, which is also a well-known feature in human PSE.10 The seizure-related anatomical changes in the GABA system further supported BRD2’s involvement in human IGE.10 The BRD2 gene expresses distinct tissue-specific transcripts that originate from different promoters and have strikingly different lengths of 50 untranslated regions (50 UTR). It was also experimentally confirmed that the presence of a highly conserved, but alternatively spliced exon would result in a premature termination of translation. These multiple levels of regulation would affect the production of functional BRD2 protein during neural development, hence its role in the etiology of seizure susceptibility.11 The association between JME/PPR and the BRD2 gene has been reported with different alleles in different studies. Furthermore some population studies have shown association with the promoter region, whereas the others with the 3-end. On the other hand, the replication studies for both regions failed in some
648
E.N. Yavuz et al. / Seizure 21 (2012) 646–648
other reported samples. Lorenz et al. reported an association between markers in the BRD2 region and PPR in German individuals, 59% of whom also had IGE.5 A following multi-center study typed a single SNP (the promoter variant rs3918149) in the promoter of JME patients from five independent European populations consisting of 531 JME cases and 1390 healthy controls. They observed a significant effect in a small sample recruited in Britain, a borderline significant effect in a sample recruited in Ireland and no associations in larger samples of German, Australian, and Indian populations, interestingly.12 The Dutch group further investigated three SNP markers in the 3-end of the BRD2 gene showing the strongest association in the study with German individuals. They found no significant difference between the allele frequencies in cases and controls for these chosen markers.13 Due to these inconclusive results, we investigated this plausible gene with a different technique in a different ethnic cohort. Our results suggested that mutations of the BRD2 gene did not seem to be frequently associated with idiopathic photosensitive epilepsy in Turkish epileptic patients. Due to the lack of a healthy control group in our study, our results should be interpreted with caution. We want to emphasize that there is currently no diagnostic role of the BRD2 gene investigations in clinical practice. We also tested a hypothesis that SNP changes of the BRD2 gene might be clinically relevant. The comparison of the patients showing these SNP changes with the remaining patients suggested a link between carrier status and prognosis. It was interesting to note that a poor prognosis for PSE (no remission for 2 years under appropriate anti-epileptic drug therapy) is more common in the group without any SNP changes of the BRD2 gene. This peculiar result may indicate a potential protective or therapy modulating effect of SNP changes of the BRD2 gene but this finding needs to be verified by larger studies. In conclusion, our study did not confirm the presence of the genetic variants previously found to link the BRD2 gene to the idiopathic form of photosensitive epilepsy in Turkish patients.
Acknowledgement This study was supported by the Scientific Research Projects Fund of Istanbul University (project no. 2007-1407). References 1. Kasteleijn-Nolst-Trenite´ DG. Photosensitivity, visually sensitive seizures and epilepsies. Epilepsy Research 2006;70:S269–79. 2. Yavuz EN, Demirkan A, Moen S, Ozdemir O, Catal S, Bebek N, et al. Investigation of the relationship between clinical and EEG findings of photosensitive epilepsy and GABA receptor alpha 1 subunit (GABRA1) gene mutations. Archives of Neuropsychiatry 2011;48:39–43. http://www.noropsikiyatriarsivi.com/sayilar/ 402/buyuk/39-43.pdf. 3. Taylor I, Marini C, Johnson MR, Turner S, Berkovic SF, Scheffer IE. Juvenile myoclonic epilepsy and idiopathic photosensitive occipital lobe epilepsy: is there overlap? Brain 2004;127:1878–86. 4. Baykan B, Matur Z, Gures C, Aykutlu E, Gokyigit A. Typical absence seizures triggered by photosensitivity. Epilepsia 2005;46:159–63. 5. Lorenz S, Taylor KP, Gehrmann A, Becker T, Muhle H, Gresch M, et al. Association of BRD2 polymorphisms with photoparoxysmal response. Neuroscience Letters 2006;400:135–9. 6. Pal DK, Evgrafov OV, Tabares P, Zhang F, Durner M, Greenberg DA. BRD2 (RING3) is a probable major susceptibility gene for common juvenile myoclonic epilepsy. American Journal of Human Genetics 2003;73:261–70. 7. Striano S, Coppola A, Del Gaudio L, Striano P. Reflex seizures and reflex epilepsies: old models for understanding mechanisms of epileptogenesis. Epilepsy Research 2012. http://dx.doi.org/10.1016/j.eplepsyres.2012.01.013. 8. Durner M, Sander T, Greenberg DA, Johnson K, Beck-Mannagetta G, Janz D. Localization of idiopathic generalized epilepsy on chromosome 6p in families of juvenile myoclonic epilepsy patients. Neurology 1991;41:1651–5. 9. Sander T, Bockenkamp B, Hildmann T, Blasczyk R, Kretz R, Wienker TF, et al. Refined mapping of the epilepsy susceptibility locus EJM1 on chromosome 6. Neurology 1997;49:842–7. 10. Velı´sˇek L, Shang E, Velı´sˇkova´ J, Chachua T, Macchiarulo S, Maglakelidze G, et al. GABAergic neuron deficit as an idiopathic generalized epilepsy mechanism: the role of BRD2 haploinsufficiency in juvenile myoclonic epilepsy. PLoS One 2011;6(8):e23656. 11. Shang E, Cui Q, Wang X, Beseler C, Greenberg DA, Wolgemuth DJ. The bromodomain-containing gene BRD2 is regulated at transcription, splicing, and translation levels. Journal of Cellular Biochemistry 2011;112:278493. 12. Cavalleri GL, Walley NM, Soranzo N, Mulley J, Doherty CP, Kapoor A, et al. A multicenter study of BRD2 as a risk factor for juvenile myoclonic epilepsy. Epilepsia 2007;48:706–12. 13. de Kovel CG, Pinto D, de Haan GJ, Kasteleijn-Nolst Trenite´ DG, Lindhout D, Koeleman BP. Association analysis of BRD2 (RING3) and epilepsy in a Dutch population. Epilepsia 2007;48:2191–2.
Contents lists available at SciVerse ScienceDirect
Seizure journal homepage: www.elsevier.com/locate/yseiz
Short communication
Bromodomain-Containing Protein 2 gene in photosensitive epilepsy§ Ebru Nur Yavuz a, Ozkan Ozdemir b, Suzin Catal b, Nerses Bebek a,b, Ugur Ozbek b, Betul Baykan a,b,* a b
Istanbul University, Istanbul Faculty of Medicine, Department of Neurology and Istanbul University Epilepsy Center, Turkey Istanbul University, Institute of Experimental Medicine (DETAE), Department of Genetics, Turkey
A R T I C L E I N F O
A B S T R A C T
Article history: Received 1 April 2012 Received in revised form 31 May 2012 Accepted 2 June 2012
Purpose: Photosensitive epilepsy (PSE) is a form of reflex epilepsy characterized by seizures triggered by light. Genetic factors play an important role and some studies have indicated a possible role of the Bromodomain-Containing Protein 2 (BRD2) gene. Our aim was to investigate the relationship between PSE and mutations of the BRD2 gene. Methods: Fifty-four PSE patients with normal findings on neurological examination and neuro-imaging studies were included. All had a clear photoparoxysmal response in the EEG as reported by 2 experienced EEG interpreters. We investigated the BRD2 gene by denaturing high performance liquid chromatography followed by direct DNA sequencing. Results: We failed to detect any mutations of the BRD2 gene. However, several single-nucleotide polymorphisms (SNPs) were observed in the gene; three of them were novel SNPs. The comparison of the patients showing these SNP changes with the remaining patients suggested a link between carrier status and prognosis. Conclusion: Our study did not confirm the presence of the genetic variants previously found to link the BRD2 gene to the idiopathic form of photosensitive epilepsy. SNP changes of the BRD2 gene may be clinically relevant but these findings need to be verified by larger studies. ß 2012 British Epilepsy Association. Published by Elsevier Ltd. All rights reserved.
Keywords: Photosensitive epilepsy BRD2 gene Epilepsy genetics Juvenile myoclonic epilepsy Mutation Polymorphism
1. Introduction Photosensitivity is an abnormal, exaggerated response of the brain to light defined by the occurrence of spikes or spikes and waves in response to intermittent photic stimulation (IPS) in the electroencephalogram (EEG).1,2 Photosensitive epilepsy (PSE) is a heterogeneous genetic epilepsy with seizures triggered by IPS or daily light sources.1,2 Photosensitivity is frequently observed in idiopathic (genetic) generalized epilepsy (IGE) especially in its subtypes juvenile myoclonic epilepsy (JME), childhood and juvenile absence epilepsy, and also in the idiopathic photosensitive occipital lobe epilepsy (IPOE).3,4 Although PSE is commonly observed in the neurology practice, its pathophysiology has not yet been explained. Genetic factors play an important role and one study has indicated a relation with the Bromodomain-Containing Protein 2 (BRD2) gene.5 Highly
§
This study was presented in a preliminary form as a poster in the 63rd Annual American Academy of Neurology Meeting, held in Toronto on April 10–17, 2010. The study was approved by the Ethics Committee of the Istanbul Faculty of Medicine (23.5.2007-05). * Corresponding author at: Istanbul University, Istanbul Faculty of Medicine, Department of Neurology, Millet Cad, 34390 Capa, Istanbul, Turkey. Tel.: +90 212 414 2000x32598; fax: +90 212 533 4393. E-mail addresses: [email protected], [email protected] (B. Baykan).
significant linkage disequilibrium (LD) was shown between JME and a core haplotype of five single-nucleotide-polymorphism (SNP) and microsatellite markers with LD peaking in the BRD2 (RING3) gene.6 Lorenz et al. reported allelic and haplotypic associations between photoparoxysmal response (PPR) and six BRD2 polymorphisms in 187 subjects exhibiting PPR and 666 healthy controls.5 Considering the strong neurobiological association of JME with PPR, these results suggested that PPR and JME may share epileptogenic pathways, for which the BRD2 gene variations might be an underlying susceptibility factor.5 Our aim was to investigate the relationship between idiopathic PSE and the mutations or polymorphisms of the BRD2 gene in a group of Turkish patients. We also assessed whether patients with variants of BRD2 differ from patients without these variants. 2. Materials and methods We included 54 patients with idiopathic/genetic epilepsy having a clear photoparoxysmal response in at least one EEG as reported by 2 experienced interpreters. All participants had normal findings on neurological examination and neuro-imaging studies. The patients with epileptic discharges during resting EEG or during hyperventilation had at least two-fold or more increase in the epileptic discharges during IPS. All patients were followed up by the same Epilepsy Center at least for 2 years to determine the prognosis. They underwent interictal or ictal EEG studies. EEG
1059-1311/$ – see front matter ß 2012 British Epilepsy Association. Published by Elsevier Ltd. All rights reserved. http://dx.doi.org/10.1016/j.seizure.2012.06.008
E.N. Yavuz et al. / Seizure 21 (2012) 646–648
investigations were performed using a standard IPS scheme. It started eyes open for 5 s and then eyes closed for 5 s; the stimulus train was given in a screening phase with 5–10–15–20–25–30– 35 Hz as described elsewhere.4 Clinical photosensitivity was defined as the self-report of the patients stating that their seizures were induced by light during daily life (sunlight, TV, video games, patterns, etc.). All patients’ clinical and EEG files were evaluated in detail for characteristics such as sex, current age, median age at onset, triggers for seizures in daily life, seizure types and syndrome classification. An epilepsy syndrome diagnosis was made for each patient, based on the clinical and EEG features according to the International League Against Epilepsy (ILAE) classification. The patients with myoclonia as the predominant seizure type were diagnosed as juvenile myoclonic epilepsy, whereas the others having absence seizures were grouped according to the age at onset before and after 10 years, as childhood or juvenile absence epilepsy. The study was approved by the local ethics committee and all patients gave written informed consent. The remission for 2 years and relapses were also evaluated. DNA was extracted from blood samples using Qiagen DNA extraction kit. Specific primers for each exon, including exon– intron boundary sites were designed with the BRD2 sequence taken from NCBI (NM_001113182.2) database by using ‘‘primer3’’ software (http://frodo.wi.mit.edu/primer3/). After optimization stage, polymerase chain reaction (PCR) was performed for all 13 exons and PCR products were controlled with 3% agarose gel electrophoresis. Amplified PCR products were scanned through the dHPLC (denaturing high-performance liquid chromatography) system (WAVE System Model 3500 HT) in specific conditions. Denaturation patterns of all amplicons were carefully investigated and those samples having any deflection over others were confirmed by bidirectional sequencing (for both 50 and 30 strands). We used Fisher’s exact test to compare clinical findings between the group of patients who have at least one variation and the group of patients without variation. P values less than 0.05 were considered statistically significant. 3. Results There were 40 women and 14 men diagnosed with PSE and their current ages were between 12 and 63 years. The median age at onset of the seizures was 13.1 5.5 years. Fifty-two patients were diagnosed with IGE (34 with JME, 4 with childhood absence epilepsy, 10 with juvenile absence epilepsy, 4 with late-onset IGE) and the remaining two patients were diagnosed with IPOE.4 All patients had PPR in the EEG and 43 patients also reported seizures triggered by light in their daily life (TV in 16 pts, sunlight in 17, computer/video 7 pts, patterns 4 pts). The variants found after sequencing analysis are presented in Table 1. Three unknown variants were found, but none of them Table 1 Sequenced samples and variations of the BRD2 gene. Number of patientsa
Variant
Position
Aminoacid Change
2 2 2 1b 13 1b 6 1 2b
rs9276935; heterozygous rs55912052; heterozygous rs516535; heterozygous c.177C>A; heterozygous rs15912; hetero-homozygous c.2147-10A>C rs2071876; heterozygous rs3918140; heterozygous c.3053G>A
50 UTR 50 UTR Exon 3 Exon 3 Exon 6 Intron Exon 13 Exon 13 30 UTR
– – Lys > Lys Ala > Ala Leu > Leu – Ser > Ser Ser > Ser –
a b
Some patients have more than one variation. Unknown variants.
647
Table 2 Comparison of patients with and without SNP changes in the BRD2 gene.
Poor prognosis (no remission) 1st degree consanguineous marriage Family history of epilepsy JME syndrome Recorded seizure during IPS Absence seizures Generalized tonic–clonic convulsions
Group1 (n: 26)
Group2 (n: 28)
P value
8 5 16 18 8 10 22
17 5 10 16 14 13 22
0.03a Ns Ns Ns Ns Ns Ns
JME, juvenile myoclonus epilepsy; IPS, intermittent photic stimulation; ns, not significant. Group 1, patients with single nucleotide polymorphism in the BRD2 gene. Group 2, patients without SNPs in the BRD2 gene. a Fisher’s exact test.
cause any aminoacid change or splicing defect. The other variants were well-known polymorphisms. We compared the clinical and EEG features of the patients showing these SNP changes (26 cases), with the remaining patients without any SNP changes (28 patients) using the nonparametric Fisher’s exact test. We found a statistically significant association of the SNPs in the BRD2 gene with the prognosis (which is defined as seizure remission for 2 years under anti-epileptic drug therapy for 26 patients versus no remission in 28 patients, P = 0.03) as shown in Table 2. 4. Discussion Reflex seizures and epilepsies are well-known entities, which create a human model that can help with the understanding of the basic mechanisms underlying epilepsy. The increased risk of exposure to potentially ictogenic artificial light sources associated with modern life makes photosensitive epilepsy (PSE) an important issue to study.7 The chromosomal region on 6p21 has shown linkage to various IGE syndromes, particularly to JME and also PSE.8,9 The BRD2 gene, a putative nuclear transcriptional regulator from a family of genes that are expressed during development, is a good positional candidate. Pal et al. reported two JME-associated SNP variants in the BRD2 (RING3) promoter region and suggested that the BRD2 gene is EJM1, the first gene identified for JME.6 These findings also suggested that abnormalities of neural development may cause common idiopathic epilepsy.6 Recently, in a heterozygous BRD2+/ mice model, Velı´sˇek et al. reported that the non-channel-encoding, developmentally critical BRD2 gene is associated with sex-specific increases in the seizure susceptibility, which is also a well-known feature in human PSE.10 The seizure-related anatomical changes in the GABA system further supported BRD2’s involvement in human IGE.10 The BRD2 gene expresses distinct tissue-specific transcripts that originate from different promoters and have strikingly different lengths of 50 untranslated regions (50 UTR). It was also experimentally confirmed that the presence of a highly conserved, but alternatively spliced exon would result in a premature termination of translation. These multiple levels of regulation would affect the production of functional BRD2 protein during neural development, hence its role in the etiology of seizure susceptibility.11 The association between JME/PPR and the BRD2 gene has been reported with different alleles in different studies. Furthermore some population studies have shown association with the promoter region, whereas the others with the 3-end. On the other hand, the replication studies for both regions failed in some
648
E.N. Yavuz et al. / Seizure 21 (2012) 646–648
other reported samples. Lorenz et al. reported an association between markers in the BRD2 region and PPR in German individuals, 59% of whom also had IGE.5 A following multi-center study typed a single SNP (the promoter variant rs3918149) in the promoter of JME patients from five independent European populations consisting of 531 JME cases and 1390 healthy controls. They observed a significant effect in a small sample recruited in Britain, a borderline significant effect in a sample recruited in Ireland and no associations in larger samples of German, Australian, and Indian populations, interestingly.12 The Dutch group further investigated three SNP markers in the 3-end of the BRD2 gene showing the strongest association in the study with German individuals. They found no significant difference between the allele frequencies in cases and controls for these chosen markers.13 Due to these inconclusive results, we investigated this plausible gene with a different technique in a different ethnic cohort. Our results suggested that mutations of the BRD2 gene did not seem to be frequently associated with idiopathic photosensitive epilepsy in Turkish epileptic patients. Due to the lack of a healthy control group in our study, our results should be interpreted with caution. We want to emphasize that there is currently no diagnostic role of the BRD2 gene investigations in clinical practice. We also tested a hypothesis that SNP changes of the BRD2 gene might be clinically relevant. The comparison of the patients showing these SNP changes with the remaining patients suggested a link between carrier status and prognosis. It was interesting to note that a poor prognosis for PSE (no remission for 2 years under appropriate anti-epileptic drug therapy) is more common in the group without any SNP changes of the BRD2 gene. This peculiar result may indicate a potential protective or therapy modulating effect of SNP changes of the BRD2 gene but this finding needs to be verified by larger studies. In conclusion, our study did not confirm the presence of the genetic variants previously found to link the BRD2 gene to the idiopathic form of photosensitive epilepsy in Turkish patients.
Acknowledgement This study was supported by the Scientific Research Projects Fund of Istanbul University (project no. 2007-1407). References 1. Kasteleijn-Nolst-Trenite´ DG. Photosensitivity, visually sensitive seizures and epilepsies. Epilepsy Research 2006;70:S269–79. 2. Yavuz EN, Demirkan A, Moen S, Ozdemir O, Catal S, Bebek N, et al. Investigation of the relationship between clinical and EEG findings of photosensitive epilepsy and GABA receptor alpha 1 subunit (GABRA1) gene mutations. Archives of Neuropsychiatry 2011;48:39–43. http://www.noropsikiyatriarsivi.com/sayilar/ 402/buyuk/39-43.pdf. 3. Taylor I, Marini C, Johnson MR, Turner S, Berkovic SF, Scheffer IE. Juvenile myoclonic epilepsy and idiopathic photosensitive occipital lobe epilepsy: is there overlap? Brain 2004;127:1878–86. 4. Baykan B, Matur Z, Gures C, Aykutlu E, Gokyigit A. Typical absence seizures triggered by photosensitivity. Epilepsia 2005;46:159–63. 5. Lorenz S, Taylor KP, Gehrmann A, Becker T, Muhle H, Gresch M, et al. Association of BRD2 polymorphisms with photoparoxysmal response. Neuroscience Letters 2006;400:135–9. 6. Pal DK, Evgrafov OV, Tabares P, Zhang F, Durner M, Greenberg DA. BRD2 (RING3) is a probable major susceptibility gene for common juvenile myoclonic epilepsy. American Journal of Human Genetics 2003;73:261–70. 7. Striano S, Coppola A, Del Gaudio L, Striano P. Reflex seizures and reflex epilepsies: old models for understanding mechanisms of epileptogenesis. Epilepsy Research 2012. http://dx.doi.org/10.1016/j.eplepsyres.2012.01.013. 8. Durner M, Sander T, Greenberg DA, Johnson K, Beck-Mannagetta G, Janz D. Localization of idiopathic generalized epilepsy on chromosome 6p in families of juvenile myoclonic epilepsy patients. Neurology 1991;41:1651–5. 9. Sander T, Bockenkamp B, Hildmann T, Blasczyk R, Kretz R, Wienker TF, et al. Refined mapping of the epilepsy susceptibility locus EJM1 on chromosome 6. Neurology 1997;49:842–7. 10. Velı´sˇek L, Shang E, Velı´sˇkova´ J, Chachua T, Macchiarulo S, Maglakelidze G, et al. GABAergic neuron deficit as an idiopathic generalized epilepsy mechanism: the role of BRD2 haploinsufficiency in juvenile myoclonic epilepsy. PLoS One 2011;6(8):e23656. 11. Shang E, Cui Q, Wang X, Beseler C, Greenberg DA, Wolgemuth DJ. The bromodomain-containing gene BRD2 is regulated at transcription, splicing, and translation levels. Journal of Cellular Biochemistry 2011;112:278493. 12. Cavalleri GL, Walley NM, Soranzo N, Mulley J, Doherty CP, Kapoor A, et al. A multicenter study of BRD2 as a risk factor for juvenile myoclonic epilepsy. Epilepsia 2007;48:706–12. 13. de Kovel CG, Pinto D, de Haan GJ, Kasteleijn-Nolst Trenite´ DG, Lindhout D, Koeleman BP. Association analysis of BRD2 (RING3) and epilepsy in a Dutch population. Epilepsia 2007;48:2191–2.