early growth response ( egr ) genes , which include egr1 , egr2 , egr3 , and egr4 , encode dna - binding transcription factors that contain cys2-his2 zinc fingers ( beckmann and wilce , 1997 ; o'donovan et al . , 1999 ) . the egr genes encode a family of immediate early gene transcription factors that mediate the transcription of various genes related to neuronal development and plasticity , cognition , circadian rhythm , and social behaviors ( beckmann and wilce , 1997 ; morris et al . , 1998 ; o'donovan et al . , 1999 ; davis et al . , 2003 ; knapska and kaczmarek , 2004 ; james et al . , 2006 ; baumgartel et al . , 2008 ; poirier et al . , 2008 ) , which have been implicated in the pathophysiology of schizophrenia ( spr ) and bipolar disorder ( bd ) . egrs are involved in rodent models of psychotic disorders ( gallitano - mendel et al . , 2007 , 2008 ) , as well as in the action mechanisms of antipsychotics and electroconvulsive seizures ( yamagata et al . , 1994 ; jung et al . , 1996 ; verma et al . , 2007 ) . moreover , downregulation of egr1 , egr2 , and egr3 transcripts in the postmortem brains of patients with spr has been reported ( yamada et al . , 2007 ) . in particular , egr3 has a strong , consistent association with spr in both family - based and case - control association studies in japanese cohorts ( yamada et al . , 2007 ) . , 2010b ) , while a negative association has been reported in a chinese population ( liu et al . , additionally , a genetic association between egr3 and bipolar disorder was recently reported ( mansour et al . , 2009 ) . although egrs encode closely related transcription factors that contain cys2-his2 zinc fingers that can bind to the same cognate gc - rich consensus dna binding motif , individual egr genes have little sequence homology outside the common dna - binding domain . furthermore , they are regulated by different signal pathways and serve different functions ( beckmann and wilce , 1997 ; herdegen and leah , 1998 ; poirier et al . , 2008 ) . in certain circumstances , they may even have antagonistic functions ; for example , egr1 and egr2 exert opposing influences on adipocyte differentiation ( boyle et al . , 2009 ) and t cell receptor - induced changes in t cell function ( collins et al . , 2008 ) . additionally , egr2 has been reported to have different effects on cognitive function than other egr genes ( poirier et al . , 2007 ) . the human egr2 gene resides at chromosomal location 10q21.3 , which the linkage analysis has identified as a susceptibility locus for bd ( venken et al . , the linked regions could contain multiple susceptibility genes showing association ( straub and weinberger , 2006 ) . for example , ankyrin g ( ank3 ) , one of the most promising susceptibility genes for bd , is also located at chromosome 10q21 ( ferreira et al . , 2008 ; schulze et al . , 2009 ; smith et al . , egr2 is involved in regulating bcl-2 family protein and mitochondrial function ( unoki and nakamura , 2003 ; lauritsen et al . , 2008 ) , which are thought to be involved in the pathophysiology of bd ( kato , 2006 ; marmol , 2008 ; andreazza et al . , 2010 ; kim et al . , egr2 plays important roles in peripheral nerve myelination , t cell maturation , hindbrain segmentation , and lipid biosynthesis ( schneider - maunoury et al . , 1993 ; swiatek and gridley , 1993 ; topilko et al . , 1994 ; leblanc et al . , 2005 ) . as noted above , the involvement of egr2 in cognitive behavioral phenotypes have been reported . an attention set shifting task induced the expression of egr2 , but not egr1 or egr3 , in the frontal cortex of mice ( desteno and schmauss , 2008 ) . forebrain - specific egr2-deficient mice demonstrated enhanced long - term object recognition memory and superior implicit motor skill learning abilities ( poirier et al . , 2007 ) , in sharp contrast to the behavioral phenotypes of egr3-deficient mice , which had poor long- and short - term memory ( gallitano - mendel et al . , 2007 ) . these findings suggest that egr2 has different effects of on brain functions than other egr genes . given the possible relationship between egr2 and bd , we investigated the association of egr2 with bd in a korean population . we also extended the investigation to the association of egr2 with spr , which showed negative associations in previous korean and chinese case control association studies ( kim et al . , 2010b ; liu et al . , 2010 ) and positive findings in a family - based association study done in japanes population ( yamada et al . , 2007 ) nine snps within the 15-kb region surrounding the egr2 gene were selected as described in methods . snp information , including the relative location of the snps on the egr2 gene , is presented in figure 1 . of the nine investigated snps of egr2 , rs2295814 ( snp3 ) , rs61865882 ( snp4 ) , rs10995315 ( snp6 ) , rs2297488 ( snp7 ) , and rs2297489 ( snp8 ) showed significant allelic associations with bd ( p = 0.0027 , 0.0008 , 0.0020 , 0.0103 , and 0.0011 for each snp , respectively ) . these snps also showed genotypic associations with bd ( p = 0.0026 , 0.0011 , 0.0068 , 0.0240 , and 0.0048 for each snp , respectively ) . the frequencies of the a , c , a , a , and g alleles in snp 3 , 4 , 6 , 7 , and 8 , respectively , were significantly increased in the bd group compared to the controls , and all withstood multiple testing correction with 10,000 permutations ( ppermutation = 0.0164 , 0.0056 , 0.0127 , 0.0460 , and 0.0074 for each snp , respectively ) . additionally , the positive associations with bd in snp 3 , 4 , 6 , and 8 remained significant after the bonferroni correction ( p < 0.0028 ) . the other four snps of egr2 [ rs9990 ( snp1 ) , rs1509963 ( snp2 ) , rs45602133 ( snp5 ) , and rs224278 ( snp9 ) ] did not show significant associations with bd in allele - wise or genotype - wise analyses . additionally , no significant association was found between the examined egr2 snps and the spr group . association results for rs2295814 and rs2297488 with the spr group from our previous study ( kim et al . the genotypic distributions of all snps were found to be in hardy - weinberg equilibrium ( hwe ) in the control , bd , and spr groups . the allelic and genotypic frequencies of the nine snps of egr2 in the three groups are summarized in table 1 . high levels of ld between snps 2 and 3 , and among snps 6 , 7 , and 8 were found , as reflected by the squared correlation coefficients ( r ) , for the snps that showed significant positive associations with bd . the ld block structure was calculated using the solid spine method ( d ' > 0.8 ) implemented within haploview , which demonstrated that five snps ( snps 1 to 5 ) and the remaining four snps ( snps 6 to 9 ) formed distinct haplotype blocks ( blocks 1 and 2 ) . the ld pattern of egr2 is presented in figure 1 . we performed a haplotype analysis of the haplotype blocks formed by the ld structure of the egr2 gene . regarding haplotype block 1 , four common haplotypes ( frequency > 5% ) were analyzed and the ' c - g - g - t - t ( snp1 - 5 ) ' haplotype was significantly under - represented ( p = 0.0422 ,  = 4.126 , or = 0.805 ) , while the ' t - g - a - c - t ' haplotype was significantly over - represented ( p = 0.0035 ,  = 8.548 , or = 1.736 ) in the bd group compared with the controls . additionally , among the three common haplotypes ( frequency > 5% ) of haplotype block 2 , the ' a - a - g - c ( snp5 - 8 ) ' haplotype was significantly over - represented in the bd group compared to the controls ( p = 0.0091 ,  = 6.807 , or = 1.543 ) . however , there was no significant haplotypic association with the spr group ( data not shown ) . the frequencies of the egr2 haplotypes in the control and bd groups are summarized in table 2 . in this study , we found a genetic association between egr2 and bd in korea . of the nine egr2 snps examined , five [ snp3 ( rs2295814 ) , snp4 ( rs61865882 ) , snp6 ( rs10995315 ) , snp7 ( rs2297488 ) , and snp8 ( rs2297489 ) ] showed significant allelic and genotypic associations with bd . additionally , the ' t - g - a - c - t ( snp1 - 5 ) ' and ' a - a - g - c ( snp6 - 9 ) ' haplotypes were over - represented , while the ' c - g - g - t - t ( snp1 - 5 ) ' haplotype was under - represented in the bd subjects . in contrast , there was no association between the examined snps of egr2 and spr . these findings provide provisional evidence that egr2 may be a susceptibility gene for bd . to our knowledge , this is the first report of a positive association of egr2 with bd . five snps in the egr2 gene , which showed a ld trend , were found to be associated with bd . significant positive associations of four egr2 snps ( snps 3 , 4 , 6 , and 8) remained after the multiple testing correction with permutation analysis and the bonferroni correction . minor alleles of the associated snps , a , c , a , a , g in snp 3 , 4 , 6 , 7 , and 8 , respectively , were over - represented in the bd group . consistently , the haplotypes containing these alleles , ' t - g - a - c - t ( snp1 - 5 ) ' in haplotype block 1 and ' a - a - g - c ( snp6 - 9 ) ' in haplotype block 2 , were significantly over - represented in the bd group . although an extended analysis with a larger sample size or independent replication is required , these findings suggest that egr2 may be related to the development of bd . of the associated egr2 snps , snps 7 and 8 ( rs2297488 and rs2297489 ) egr2 expression is upregulated through intronic cpg islands methylation ( unoki and nakamura , 2003 ) , and the binding of methyl - cpg - binding protein 2 ( mecp2 ) , which plays important roles in neurodevelopment ( gonzales and lasalle , 2010 ) , to this region upregulates egr2 expression ( swanberg et al . , 2009 ) . the c / g polymorphism in snp8 is associated with a sequence change from cc to cg [ 5'-ccacc(c / g)ccatc-3 ' ] , which can add a cpg site for methylation . changes in nucleotide sequences related to polymorphisms creating additional cpg sites can affect the dna methylation and transcriptional activity ( moser et al . , 2009 ) . these findings suggest a possible function of bd - associated intronic snps of egr2 regulating gene expression via alterations in dna methylation , which requires further examination . in the central nervous system ( cns ) , egr2 expression is abundant in neurons ( herdegen et al . , 1993 ) , and it is expressed strongly in layers ii and iii of the cortical regions of the brain ( beckmann and wilce , 1997 ) , where the reduction in neuronal density is most prominent in the postmortem brains of patients with mood disorders ( rajkowska , 2000 ) . forebrain - specific knockout of egr2 in mice induced enhanced motor skill learning and long - term memory , indicating an inhibitory role of egr2 in certain cognitive functions ( poirier et al . egr2 is induced in the prefrontal cortex of mice performing attention set - shifting ( desteno and schmauss , 2008 ) , dysfunction of which has been implicated as an endophenotype of bd ( clark et al . , egr2 is also involved in nmethyl d - aspartate ( nmda ) receptor - mediated long - term potentiation ( ltp ) and long - term depression ( ltd ) in the mouse hippocampus ( coba et al . , these findings suggest the involvement of egr2 dysregulation in the cognitive dysfunction of bd through altered levels in the brain . the function of egr2 as an intracellular signaling molecule supports its potential role in bd . egr2 is involved in the signal pathways possibly responsible for the pathogenesis of psychotic disorders , such as spr and bd , including intracellular signal transduction related to the neuregulin - erbb receptor ( jacobson et al . , 2004 ; he et al . , 2010 ) , calcineurin ( hildeman et al . , 2003 ; kao et al . , 2009 ) , and brain - derived neurotrophic factor ( glorioso et al . , 2006 ) . neuregulin 1 ( nrg1 ) gene has been reported to be associated with spr and bd ( stefansson et al . , 2002 , 2003 ; cassidy et al . , 2006 ; thomson et al . , 2007 ; georgieva et al egr2 acts as a downstream effector of the neuregulin - erbb receptor signal , which plays a critical role in peripheral nerve myelination in schwann cells ( kao et al . , 2009 ; he et al . , 2010 ) . in the cns , a different role of the neuregulin signal in brain development has been suggested , such as guiding axon pathfinding ( birchmeier , 2009 ) . these findings suggest a different role of egr2 in the cns as a downstream effector of neuregulin signals , which requires further investigation . egr2 is also involved in apoptosis and mitochondrial functions via the regulation of bcl-2 family proteins ( unoki and nakamura , 2003 ; lauritsen et al . , 2008 ) , and the involvement of dysregulation of the bcl-2 family proteins or mitochondrial function in the pathogenesis of bd has been suggested ( kato , 2006 ; marmol , 2008 ; andreazza et al . , 2010 ; kim et al . , 2010a ) . recently , we reported the association of egr3 with spr in a case - control association study in korea ( kim et al . , 2010b ) , replicating a previous japanese report ( yamada et al . , 2007 ) . however , two egr2 snps ( rs2295814 and rs2297488 ) did not show positive associations with spr ( kim et al . , 2010b ) , although they were associated with spr in a japanese family - based association analysis ( yamada et al . , 2007 ) . additionally , in the current study , seven more examined egr2 snps did not show associations with spr . a recent case - control association study in a han chinese population also demonstrated that egr2 did not show a significant association with spr ( liu et al . , 2010 ) . the possible association of egr2 with spr and the common and differential involvement of egr genes , especially egr2 and egr3 , require further clarification . as our study had a limited sample size , further extended analysis with a larger sample size or an independent replication study is required to confirm the positive association of egr2 with bd . the strong association of egr2 snps with bd , withstanding multiple testing corrections and a p value < 0.001 ( in the case of rs61865882 ) , are noteworthy , and reduce the chance of this being a false - positive finding and predict future replication ( lohmueller et al . , 2003 ) . although the possible involvement of population stratification was not tested in this study , it seems unlikely in our sample because the korean population is relatively homogeneous . in conclusion of the nine snps of egr2 examined , five showed nominal significant allelic and genotypic associations with bd , and the positive association of four snps remained significant after multiple testing correction . the human egr2 gene is located at chromosome 10q21 , one of the loci related to the pathophysiology of bd . egr2 plays important roles in cognitive function , the myelination process , and intracellular signaling , making involvement in the pathogenesis of bd plausible . this study enrolled 946 individuals : 350 controls ( 174 men , 176 women ; mean age 25.9  6.5 years ) , 352 patients with bd ( 149 men , 203 women ; average age 33.5  12.0 years ) , and 244 patients with spr ( 147 men , 97 women ; average age 32.7  7.8 years ) . all patients met the diagnostic and statistical manual of mental disorders , 4 edition ( dsm - iv ) , criteria for the diagnosis of bd or spr . patients were interviewed individually by trained researchers using the korean translation of the diagnostic interview for genetic studies ( digs ) ( joo et al . , 2004 ) . meetings with at least two psychiatrists were held regularly to arrive at consensual decisions about the participants ' final diagnoses and to eliminate subjects with organic brain disease , alcohol or drug problems , or other general medical conditions possibly manifesting as psychiatric symptoms . healthy subjects included in the control group were recruited from hospital staff members and college students who volunteered to participate . interviews conducted by a psychiatrist enabled the exclusion of subjects with histories or current evidence of psychiatric illnesses , organic mental disorders , substance abuse , or any medical conditions that might lead to mental symptoms . control subjects who had any first - degree relatives with suspected psychiatric illnesses were also excluded . the study protocol was approved by the ethics committee of seoul national university hospital , and this study was conducted in accordance with the latest version of the declaration of helsinki . written informed consent was obtained from each patient before enrollment , and only subjects able to provide informed consent were included in the study . tag snps within the 15-kb region surrounding the egr2 gene ( from 64237 to 64252 kb ) were selected in the international hapmap database ( data release # 27 , http://hapmap.ncbi.nlm.nih.gov/ ) . based on the close genetic backgrounds of the korean and japanese populations ( kim et al . , 2005 ; tian et al . , 2008 ) , the genotypes downloaded were restricted to those of the japanese population of tokyo , japan ( jpt ) . five tag snps ( rs9990 , rs1509963 , rs2295814 , rs10995315 , and rs224278 ) with minor allele frequencies ( maf ) above 10% and a minimum value of 0.8 for the r parameter were selected using the tagger algorithm ( de bakker et al . , 2005 ) snp rs2297488 , which was included in previous studies of spr in japan ( yamada et al . , 2007 ) , korea ( kim et al . , 2010b ) , and china ( liu et al . , 2010 three additional egr2 snps ( rs6186 - 5882 , rs45602133 , and rs2297489 ) with maf above 10% in east asian populations in the ncbi database ( http://www.ncbi.nlm.nih.gov/projects/snp/ ) were included in the analysis . snp information , including the relative location of the snps on the egr2 gene , is presented in figure 1 . dna was extracted from whole blood samples using a dna isolation kit ( roche applied science , indianapolis , in ) . genotyping assays were performed using the taqman method ( applied biosystems , foster city , ca ) , and high genotyping rates for all markers were achieved . the genotyping failure rates for all markers were less than 1% for the control , bd , and spr groups . snps rs2295814 and rs2297488 in the control and spr groups were genotyped in our previous study ( kim et al . , 2010b ) , and are presented together with the current findings . contingency chi - square tests or fisher 's exact test were performed to compare allele and genotype frequencies between patients and controls . correction for multiple testing was performed using a correction with 10,000 permutations with the haploview software ( ver . to avoid false - positive results due to multiple testing , we used the bonferroni correction for the nine independent loci genotyped and for the comparisons of the control group with the spr and bd groups . rare haplotypes were excluded from the analysis , while frequencies exceeding 5% were included for the analysis . this study enrolled 946 individuals : 350 controls ( 174 men , 176 women ; mean age 25.9  6.5 years ) , 352 patients with bd ( 149 men , 203 women ; average age 33.5  12.0 years ) , and 244 patients with spr ( 147 men , 97 women ; average age 32.7  7.8 years ) . all patients met the diagnostic and statistical manual of mental disorders , 4 edition ( dsm - iv ) , criteria for the diagnosis of bd or spr . patients were interviewed individually by trained researchers using the korean translation of the diagnostic interview for genetic studies ( digs ) ( joo et al . , 2004 ) . meetings with at least two psychiatrists were held regularly to arrive at consensual decisions about the participants ' final diagnoses and to eliminate subjects with organic brain disease , alcohol or drug problems , or other general medical conditions possibly manifesting as psychiatric symptoms . healthy subjects included in the control group were recruited from hospital staff members and college students who volunteered to participate . interviews conducted by a psychiatrist enabled the exclusion of subjects with histories or current evidence of psychiatric illnesses , organic mental disorders , substance abuse , or any medical conditions that might lead to mental symptoms . control subjects who had any first - degree relatives with suspected psychiatric illnesses were also excluded . the study protocol was approved by the ethics committee of seoul national university hospital , and this study was conducted in accordance with the latest version of the declaration of helsinki . written informed consent was obtained from each patient before enrollment , and only subjects able to provide informed consent were included in the study . tag snps within the 15-kb region surrounding the egr2 gene ( from 64237 to 64252 kb ) were selected in the international hapmap database ( data release # 27 , http://hapmap.ncbi.nlm.nih.gov/ ) . based on the close genetic backgrounds of the korean and japanese populations ( kim et al . , 2005 ; tian et al . , 2008 ) , the genotypes downloaded were restricted to those of the japanese population of tokyo , japan ( jpt ) . five tag snps ( rs9990 , rs1509963 , rs2295814 , rs10995315 , and rs224278 ) with minor allele frequencies ( maf ) above 10% and a minimum value of 0.8 for the r parameter were selected using the tagger algorithm ( de bakker et al . , 2005 ) snp rs2297488 , which was included in previous studies of spr in japan ( yamada et al . , 2007 ) , korea ( kim et al . , 2010b ) , and china ( liu et al . , 2010 three additional egr2 snps ( rs6186 - 5882 , rs45602133 , and rs2297489 ) with maf above 10% in east asian populations in the ncbi database ( http://www.ncbi.nlm.nih.gov/projects/snp/ ) were included in the analysis . snp information , including the relative location of the snps on the egr2 gene , is presented in figure 1 . dna was extracted from whole blood samples using a dna isolation kit ( roche applied science , indianapolis , in ) . genotyping assays were performed using the taqman method ( applied biosystems , foster city , ca ) , and high genotyping rates for all markers were achieved . the genotyping failure rates for all markers were less than 1% for the control , bd , and spr groups . snps rs2295814 and rs2297488 in the control and spr groups were genotyped in our previous study ( kim et al . contingency chi - square tests or fisher 's exact test were performed to compare allele and genotype frequencies between patients and controls . correction for multiple testing was performed using a correction with 10,000 permutations with the haploview software ( ver . 4.2 ) and the bonferroni correction . to avoid false - positive results due to multiple testing , we used the bonferroni correction for the nine independent loci genotyped and for the comparisons of the control group with the spr and bd groups . rare haplotypes were excluded from the analysis , while frequencies exceeding 5% were included for the analysis .
the early growth response gene 2 ( egr2 ) is located at chromosome 10q21 , one of the susceptibility loci in bipolar disorder ( bd ) . 
 egr2 is involved in cognitive function , myelination , and signal transduction related to neuregulin - erbb receptor , bcl-2 family proteins , and brain - derived neurotrophic factor . 
 this study investigated the genetic association of the egr2 gene with bd and schizophrenia ( spr ) in korea . in 946 subjects ( 
 350 healthy controls , 352 patients with bd , and 244 with spr ) , nine single nucleotide polymorphisms ( snps ) in the egr2 gene region were genotyped . 
 five snps showed nominally significant allelic associations with bd ( rs2295814 , rs61865882 , rs10995315 , rs2297488 , and rs2297489 ) , and the positive associations of all except rs2297488 remained significant after multiple testing correction . 
 linkage disequilibrium structure analysis revealed two haplotype blocks . among the common identified haplotypes ( frequency > 5% ) , ' 
 t - g - a - c - t ( block 1 ) ' and ' a - a - g - c ( block 2 ) ' haplotypes were over - represented , while ' c - g - g - t - t ( block 1 ) ' haplotype was under - represented in bd . in contrast 
 , no significant associations were found with spr . 
 although an extended analysis with a larger sample size or independent replication is required , these findings suggest a genetic association of egr2 with bd . 
 combined with a plausible biological function of egr2 , the egr2 gene is a possible susceptibility gene in bd .