First family-based test for association of neuregulin with bipolar affective disorder

The Association Between Schizophrenia Risk Variants and Creativity in Healthy Han Chinese Subjects

Although previous evidence has suggested that there is a genetic link between schizophrenia and creativity, the specific genetic variants that underlie the link are still largely unknown. To further explore the potential genetic link between schizophrenia and creativity, in a sample of 580 healthy Han Chinese subjects, this study aimed to (1) validate the role of Neuregulin 1 (NRG1) rs6994992 (one schizophrenia risk variant that has been previously linked to creativity in the European population) in the relationship between schizophrenia and creativity and (2) explore the associations between 10 other schizophrenia risk variants and creativity. For NRG1 rs6994992, the result validated its association with creativity measures. However, since NRG1 rs6994992 is not a schizophrenia risk variant in the Han Chinese population, the validated association suggested that ethnic difference may exist in the relationship between NRG1 rs6994992, schizophrenia and creativity. For other schizophrenia risk variants, the result only demonstrated a nominal association between ZNF536 rs2053079 and creativity measures which would not survive correction for multiple testing. No association between polygenic risk score for these 10 schizophrenia risk variants and creativity measures was observed. In conclusion, this study provides limited evidence for the associations between these schizophrenia risk variants and creativity in healthy Han Chinese subjects. Future studies are warranted to better understand the potential genetic link between schizophrenia and creativity.

Association of the 3' region of the neuregulin 1 gene with bipolar I disorder in the Chinese Han population

BACKGROUND

Based on the function of neuregulin 1 (NRG1) in neurodevelopment, susceptibility to bipolar disorder presumably involves this gene. The 3' region of NRG1 contains the majority of the coding exons, and transcripts from this region encode 8 of the 9 known NRG1 isoforms; therefore, this region is likely to be predominant versus the 5' region in terms of their relative contributions to NRG1 function. We investigated the association between the 3' region of the NRG1 gene and bipolar I disorder (BPI) in the Chinese Han population and performed further analyses depending on the presence or absence of psychotic features.

METHODS

A total of 385 BPI patients and 475 healthy controls were recruited for this study. Thirty tag single nucleotide polymorphisms (SNPs) across the 3' region of the NRG1 gene were genotyped for allelic and haplotypic associations with BPI and subgroups with psychotic features (BPI-P) or without psychotic features (BPI-NP).

RESULTS

Individual marker analysis showed that 2 SNPs (rs12547858 and rs6468121) in this region were significantly associated with BPI. Moreover, subgroup analyses showed significant but marginal associations of rs6468121 with BPI-P and rs3757933 with BPI-NP. Haplotype analyses showed that 6 haplotypes were associated with BPI only.

LIMITATIONS

The sample size was relatively small. The investigated tag SNPs only represented 83% of the information on the targeted region. There might be a retrospective bias in the subgroup analyses.

CONCLUSION

The results suggest that the 3' region of the NRG1 gene plays a role in BPI susceptibility in the Chinese Han population. In addition, the preliminary results show that BPI with psychotic features and BPI without psychotic features may constitute different sub-phenotypes; however, this finding should be confirmed in a larger population sample.

Case-control association study of 36 single-nucleotide polymorphisms within 10 candidate genes for major depression and bipolar disorder

In this study we investigated 36 single nucleotide polymorphisms within 10 genes previously associated with major depression and bipolar disorder, as well as with the response to their treatment (ABCB1, ABCB4, TAP2, CLOCK, CPLX1, CPLX2, SYN2, NRG1, 5HTR1A and GPRIN2). No association with mood disorders and clinical outcomes was observed.

DISC1: a key lead in studying cortical development and associated brain disorders

For the past decade, DISC1 has been studied as a promising lead to understand the biology underlying major mental illnesses, such as schizophrenia. Consequently, many review articles on DISC1 have been published. In this article, rather than repeating comprehensive overviews of research articles, we will introduce the utility of DISC1 in the study of cortical development in association with a wide range of developmental brain disorders. Cortical development involves cell autonomous and cell nonautonomous mechanisms as well as host responses to environmental factors, all of which involve DISC1 function. Thus, we will discuss the significance of DISC1 in forming an overall understanding of multiple mechanisms that orchestrate corticogenesis and can serve as therapeutic targets in diseases caused by abnormal cortical development.

Evidence for single nucleotide polymorphisms and their association with bipolar disorder

Bipolar disorder (BD) is a complex disorder with a number of susceptibility genes and environmental risk factors involved in its pathogenesis. In recent years, huge progress has been made in molecular techniques for genetic studies, which have enabled identification of numerous genomic regions and genetic variants implicated in BD across populations. Despite the abundance of genetic findings, the results have often been inconsistent and not replicated for many candidate genes/single nucleotide polymorphisms (SNPs). Therefore, the aim of the review presented here is to summarize the most important data reported so far in candidate gene and genome-wide association studies. Taking into account the abundance of association data, this review focuses on the most extensively studied genes and polymorphisms reported so far for BD to present the most promising genomic regions/SNPs involved in BD. The review of association data reveals evidence for several genes (SLC6A4/5-HTT [serotonin transporter gene], BDNF [brain-derived neurotrophic factor], DAOA [D-amino acid oxidase activator], DTNBP1 [dysbindin], NRG1 [neuregulin 1], DISC1 [disrupted in schizophrenia 1]) to be crucial candidates in BD, whereas numerous genome-wide association studies conducted in BD indicate polymorphisms in two genes (CACNA1C [calcium channel, voltage-dependent, L type, alpha 1C subunit], ANK3 [ankyrin 3]) replicated for association with BD in most of these studies. Nevertheless, further studies focusing on interactions between multiple candidate genes/SNPs, as well as systems biology and pathway analyses are necessary to integrate and improve the way we analyze the currently available association data.

Genetic association of the EGR2 gene with bipolar disorder in Korea

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.

NRG1 gene in recurrent major depression: no association in a large-scale case-control association study

The Neuregulin 1 (NRG1) gene was initially implicated in schizophrenia (SZ) and has recently been associated with bipolar disorder (BPD) in two studies. An association with major depressive disorder (MDD) has not yet been investigated but is warranted in view of the genetic overlap between MDD and BPD. We have performed a large-scale case-control study investigating the association between NRG1 polymorphisms and MDD, genotyping a selection of 14 single nucleotide polymorphisms (SNPs) spanning the NRG1 gene in a sample of 1,398 patients of White European ancestry with a diagnosis of MDD and 1,304 ethnically matched controls from three clinical sites in the UK. We found no single marker or haplotype associations that withstood correction for multiple testing. Our findings do not provide evidence that NRG1 plays a role in MDD or that this gene explains part of the genetic overlap with BPD.

Family-based association study of Neuregulin 1 with psychotic bipolar disorder

The Neuregulin 1 gene (NRG1) has been associated with schizophrenia, and, to a lesser extent, with bipolar disorder (BP). We investigated the association of NRG1 with BP in a large family sample, and then performed analyses according to the presence of psychotic features or mood-incongruent psychotic features. We genotyped 116 tagSNPs and four Icelandic "core" SNPs in 1,199 subjects from 314 nuclear families. Of 515 BP offspring, 341 had psychotic features, and 103 had mood-incongruent psychotic features. In single-marker and sliding window haplotype analyses using FBAT, there was little association using the standard BP or mood-incongruent psychotic BP phenotypes, but stronger signals were seen in the psychotic BP phenotype. The most significant associations with psychotic BP were in haplotypes within the 5' "core" region. The strongest global P-value was across three SNPs: NRG241930-NRG243177-rs7819063 (P = 0.0016), with an undertransmitted haplotype showing an individual P = 0.0007. The most significant individual haplotype was an undertransmitted two-allele subset of the above (NRG243177-rs7819063, P = 0.0004). Additional associations with psychotic BP were found across six SNPs in a 270 kb central region of the gene. The most 3' of these, rs7005606 (P = 0.0029), is located approximately 4 kb from the type I NRG1 isoform promoter. In sum, our study suggests that NRG1 may be specifically associated with the psychotic subset of BP; however, our results should be interpreted cautiously since they do not meet correction for multiple testing and await independent replication.

Chromosome 8p as a potential hub for developmental neuropsychiatric disorders: implications for schizophrenia, autism and cancer

Defects in genetic and developmental processes are thought to contribute susceptibility to autism and schizophrenia. Presumably, owing to etiological complexity identifying susceptibility genes and abnormalities in the development has been difficult. However, the importance of genes within chromosomal 8p region for neuropsychiatric disorders and cancer is well established. There are 484 annotated genes located on 8p; many are most likely oncogenes and tumor-suppressor genes. Molecular genetics and developmental studies have identified 21 genes in this region (ADRA1A, ARHGEF10, CHRNA2, CHRNA6, CHRNB3, DKK4, DPYSL2, EGR3, FGF17, FGF20, FGFR1, FZD3, LDL, NAT2, NEF3, NRG1, PCM1, PLAT, PPP3CC, SFRP1 and VMAT1/SLC18A1) that are most likely to contribute to neuropsychiatric disorders (schizophrenia, autism, bipolar disorder and depression), neurodegenerative disorders (Parkinson's and Alzheimer's disease) and cancer. Furthermore, at least seven nonprotein-coding RNAs (microRNAs) are located at 8p. Structural variants on 8p, such as copy number variants, microdeletions or microduplications, might also contribute to autism, schizophrenia and other human diseases including cancer. In this review, we consider the current state of evidence from cytogenetic, linkage, association, gene expression and endophenotyping studies for the role of these 8p genes in neuropsychiatric disease. We also describe how a mutation in an 8p gene (Fgf17) results in a mouse with deficits in specific components of social behavior and a reduction in its dorsomedial prefrontal cortex. We finish by discussing the biological connections of 8p with respect to neuropsychiatric disorders and cancer, despite the shortcomings of this evidence.

Neuregulin 1 and age of onset in the major psychoses

Genetic vulnerability to psychiatric illness extends across major psychiatric illness. Neuregulin 1 (NRG1) is a large gene on chromosome 8p, that has been identified as a susceptibility factor in bipolar disorder and schizophrenia. In particular, a core at risk haplotype has received considerable attention for a putative role in the pathophysiology of the major psychoses (schizophrenia and bipolar disorder). This core haplotype can be represented by three markers 478B14-848, 420M9-1395, and SNP8NRG221533. We genotyped 312 families with bipolar probands, and 120 families with schizophrenia probands. Association of the core haplotype was tested for with age-at-onset and with three phenotypes: major psychosis, schizophrenia, and bipolar disorder. Neither age of onset (P = 0.893) nor the major psychosis phenotype (P = 0.374) was associated with the core haplotype in the overall sample. Ours was the first study to investigate the NRG1 core haplotype with age of onset of major psychoses, and despite our preliminary negative findings, this area deserves further investigation.

The genetics of bipolar affective disorder

PURPOSE OF REVIEW

Molecular genetic studies of bipolar affective disorder are beginning to show some positive and reproducible findings. The most relevant of these will be reviewed.

RECENT FINDINGS

Obtaining consistent findings from whole genome scans has been hampered by small sample sizes and phenotypic heterogeneity. Recently, there have been concerted efforts to overcome these problems by combining data for meta-analysis. What has become increasingly clear is that several regions that are likely to contain genes contributing to bipolar affective disorder are also relevant to schizophrenia, a finding supported by recent twin data. Studies to date have implicated the D-amino acid oxidase activator complex (also known as G72/G30), disrupted in schizophrenia-1 and neuregulin, and have pointed to several promising linkage regions in which the genes have not yet been identified. In addition, there is some evidence to support the involvement of genetic variants in catechol-o-methyl transferase and brain-derived neurotrophic factor in the aetiology of bipolar affective disorder.

SUMMARY

Molecular genetic research in bipolar affective disorder may lead to the development of new diagnostic paradigms for classifying the psychoses and affective states. In addition, determining the functional significance of the susceptibility genes will pave the way for enhanced diagnostic accuracy and improved treatments.