Polymorphisms and Haplotypes in the YWHAE Gene Increase Susceptibility to Bipolar Disorder in Chinese Han Population
ABSTRACT
Background: Schizophrenia and bipolar disorder are 2 major psychiatric illnesses sharing some specific genetic risk factors. Increasing evidence suggests the 2 illnesses might be more closely related than previously considered.
Objective: To test this hypothesis, we investigated the allele and genotype frequencies of 11 single nucleotide polymorphisms (SNPs) and the haplotypes in these SNPs of the YWHAE gene.
Method: 1,982 patients were interviewed by 2 independent, experienced psychiatrists. Bipolar disorder diagnoses were made in strict accordance with Diagnostic and Statistical Manual of Mental Disorders, Fourth Edition (DSM-IV) criteria using the Structured Clinical Interview for DSM-IV Axis I Disorders. In 2011, we conducted this genetic association analysis between 11 SNPs in YWHAE and bipolar disorder, involving a male group and a female group.
Results: In the analysis of allele and genotype frequencies, the SNP rs1873827 increased susceptibility to bipolar disorder in the male group. The haplotype analysis of CAC in rs3752826, rs2131431, and rs1873827 in the male group (χ2 = 25.744, P = 3.97E-07, OR = 0.478 [95% CI, 0.358-0.639]) and of ACT and CAC in rs3752826, rs2131431, and rs1873827 in the female group (for ACT, χ2 = 30.365, P = 3.67E-08, OR = 0.040 [95% CI, 0.007-0.218]; for CAC, χ2 = 16.874, P = 4.04E-05, OR = 0.597 [95% CI, 0.466-0.765]) showed they are protective factors for bipolar disorder. However, the haplotype analysis of CAT in the male group (χ2 = 19.874, P = 8.39E-06, OR = 2.314 [95% CI, 1.587-3.374]) and of AAC and CAT in the female group (for AAC, χ2 = 38.561, P = 5.47E-10, OR = 7.104 [95% CI, 3.471-14.540]; for CAT, χ2 = 25.497, P = 4.52E-07, OR = 2.076 [95% CI, 1.556-2.770]) showed they are risk factors for bipolar disorder.
Conclusions: Considering the size of our sample, the results suggest that YWHAE does play a major role in bipolar disorder in the Han Chinese population.
J Clin Psychiatry 2012;73(10):e1276-e1282
© Copyright 2012 Physicians Postgraduate Press, Inc.
Submitted: April 3, 2012; accepted June 25, 2012 (doi:10.4088/JCP.12m07824).
Corresponding author: Lin He, PhD, Bio-X Institutes, Shanghai Jiao Tong University, The Central Little White House, 1954 Huashan Rd, Shanghai 200030, P.R.China ([email protected]).
Bipolar disorder (Online Mendelian Inheritance in Man [OMIM] 125480) is a major psychiatric illness that causes extreme shifts in mood, energy, and functioning. It is a genetically complex neuropsychiatric disorder like other psychiatric diseases such as schizophrenia and major depressive disorder. Psychiatrists have debated whether schizophrenia and bipolar disorder are 2 distinct mental disorders with different etiopathogenesis, course, and prognosis or whether they are more connected mental disorders, possibly representing different ends of the common pathophysiologic processes.1,2 And increasing evidence suggests that schizophrenia and bipolar disorder might be more closely related than previously considered in that they share certain specific genetic and environmental risk factors.3-6 Bipolar disorder is a manic-depressive illness that is estimated to have a lifetime prevalence of 0.8%-2.6%.7 Data from family, twin, and adoption studies provide strong evidence that bipolar disorder is predominantly a polygenic genetic disorder with high heritability.8-12
Recently, Ikeda et al13 identified the YWHAE gene as a possible susceptibility gene for schizophrenia in the Japanese population. However, in an earlier study,14 we found no association of the YWHAE gene with schizophrenia, major depressive disorder, or bipolar disorder in the Han Chinese Population. YWHAE encodes 14-3-3epsilon, which is an interacting partner of DISC1. DISC1 has been identified as a potential susceptibility gene for major psychiatric disorders, including schizophrenia, depressive disorder, and bipolar disorder. In a large Scottish pedigree, DISC1 was found to be disrupted by a translocation that cosegregated with major psychiatric illness, including schizophrenia, bipolar disorder, recurrent depression, and childhood-onset behavioral disorder.15 DISC1 has also been associated with bipolar disorder in several studies. Many researchers have recently conducted studies of its function, and DISC1 has been found to be widely distributed throughout neurons, nuclei, mitochondria, and neurites. It interacts with many proteins and is related to many functions, such as neurite extension, neuronal migration, dendrite plasticity, and neurotransmitter signaling. Several DISC1 interactors such as PDE4B have also been defined as independent genetic susceptibility factors for psychiatric illness. DISC1 is a hub protein in a multidimensional risk pathway for major psychiatric illness, and studies of this pathway are opening up opportunities for a better understanding of causality and possible intervention mechanisms.16
An interactor of DISC1, 14-3-3epsilon is encoded by YWHAE and is a subtype of the 14-3-3 protein family. This family consists of 7 subtypes (β, γ, ε, σ, η, θ/τ, and ζ) encoded by separate genes. They are involved in many processes, including cell cycle regulation, metabolism control, apoptosis, and control of gene transcription.17 YWHAH, which encodes 14-3-3ζ, is a positional and functional candidate gene for both schizophrenia and bipolar disorder.18,19 As an interacting partner of DISC1, YWHAE may also have a role to play in these psychiatric disorders. In 2005, Yanagi et al20 showed that YWHAE is associated with suicide in the Japanese population. In 2008, Ikeda et al13 reported that YWHAE is a possible susceptibility gene for schizophrenia in the Japanese population. They first identified this gene by screening 25 tag single nucleotide polymorphisms (SNPs) that covered 5 DISC1-interacting molecules (NUDEL, LIS1, YWHAE, GRB2, KIF5A). Their study also showed that rs28365859, rs34041110, rs7224258, rs3752826, rs11655548, rs2131431, and rs1873827 were significantly associated with schizophrenia in both allele and genotype analyses. Other studies21,22 have shown that patients with deletion of 17p13.3 involving YWHAE were affected by Miller-Dieker syndrome, along with cognitive impairment, shared craniofacial features, and structural abnormalities of the brain. In our earlier study14 investigating the possible relationship between the YWHAE gene and major psychiatric disorders, we genotyped 11 SNPs of YWHAE in 1,140 schizophrenia patients, 1,140 major depressive disorder patients, 1,140 bipolar disorder patients, and 1,140 normal controls of Chinese Han origin but found no association between the YWHAE gene and these major mental disorders in the Han Chinese population. However, to date, no other studies of the relationship between YWHAE and bipolar disorder have been reported.
- Our study suggests that some susceptibility may be common to both schizophrenia and bipolar disorder and that a putative, sex-dependent relationship exists between the YWHAE gene and bipolar disorder.
- Evidence from this study will be useful in influencing psychiatric research to move from reliance on a diagnostic and classification system that is based only on clinical description to a scheme that better reflects the underlying biology of the psychiatric entities encountered in our clinics.
To investigate whether the YWHAE gene plays a significant role in men or women with bipolar disorder, we focused on the YWHAE gene in bipolar disorder in Han Chinese samples involving 993 bipolar disorder patients (533 men and 460 women) and 989 normal controls (296 men and 693 women). We genotyped 11 SNPs in YWHAE, consisting of the 7 positive SNPs in the study by Ikeda et al13 (rs34041110, rs7224258, rs3752826, rs11655548, rs2131431, rs1873827, and rs28365859) and 4 additional tag SNPs (rs12452627, rs1532976, rs8064578, and rs7225165) selected from the HapMap database (http://hapmap.ncbi.nlm.nih.gov/cgi-perl/gbrowse/hapmap28_B36/; version: release #21/phase II, July 2006; population: Han Chinese in Beijing, minor allele frequencies more than 0.05) to provide a good coverage of the gene.
METHOD
Samples
In total, 993 unrelated bipolar patients (men, n = 533; women, n = 460; mean ± SD age = 36.8 ± 5.8 years), and 989 unrelated controls (men, n = 296; women, n = 693; mean ± SD age = 57.2 ± 3.7 years) were recruited. All the subjects were from Shanghai and were of Han origin. Among the 993 bipolar patients, 851 (85.6%) were diagnosed with bipolar I disorder. Two independent psychiatrists made a final diagnosis on the basis of interview data and hospital case notes. Diagnoses were made in strict accordance with Diagnostic and Statistical Manual of Mental Disorders, Fourth Edition (DSM-IV) criteria based on the Structured Clinical Interview for DSM-IV Axis I Disorders. All participating subjects signed an informed consent statement. The complete details of the entire study design and procedures involved were approved by the ethics committee of Bio-X Institutes, Shanghai Jiao Tong University. Controls were randomly selected from the Shanghai general population. DNA was extracted from peripheral blood samples of the subjects by using the phenol-chloroform method. The study was conducted in 2011.
Genotyping
Of the 11 SNPs, rs3752826, rs2131431, rs1873827, rs12452627, rs8064578, rs7224258, and rs11655548 are in the intron, and rs34041110, rs1532976, rs28365859, and rs7225165 are in the intergenic region. All the SNPs were genotyped on the ABI 7900 DNA detection platform (Applied Biosystems, Foster City, California) by using TaqMan technology. All probes and primers were designed by the Assay-by-DesignTM or Assayon-DemandTM service of Applied Biosystems. The standard polymerase chain reactions (PCRs) of 4.435 µL were carried out using TaqMan Universal PCR Master Mix reagent kits (Applied Biosystems, Foster City, California) under the guidelines provided. To ensure the accuracy of genotyping results, 4 negative controls (no DNA) and 4 duplicated samples were included in each of the 384-well plates for the quality control. Five percent of the samples were repeated, and the results were 100% concordant. All genotypes were called blind to their case status in the genotyping process.
Statistical Analysis
The χ2 test for goodness of fit was used to check for Hardy-Weinberg equilibrium in genotype distributions in patients and controls. The differences in the genotype and allele distributions between patients and controls were examined by using the χ2 test for independence. All the analyses were carried out online on a robust and user-friendly software platform.23,24 All tests were 2-tailed, and statistical significance was assumed at P < .05.
RESULTS
In the 1,982 samples, genotype distributions were in Hardy-Weinberg equilibrium for all the SNPs. The allele and genotype frequencies of the 11 SNPs of the male patient sample group and the healthy controls are listed in Table 1. The allele and genotype frequencies of the 11 SNPs of the female patient sample group and the healthy controls are listed in Table 2. The linkage disequilibrium among the 11 SNPs is shown in Figures 1 and 2. The selection criteria for haplotypes used in the haplotype analyses were the adjacent SNPs with pairwise D‘ ² > 0.70. In the analysis, haplotypes with frequencies above 0.03 were tested. According to the selection criteria, 3 SNPs (rs3752826, rs2131431, and rs1873827) with strong pairwise D‘ ² > 0.70 were in 1 block, both in the male and female groups. Total results for haplotypes in the male and female groups are listed in Table 3.
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In the male group, only the allele and genotype P values for rs1873827 are associated with bipolar disorder (allele, P = 0.013298; genotype, P = 0.025579; OR = 0.768045 [95% CI, 0.623133-0.946658]) (Table 1). In Table 2, all the allele and genotype P values for the 11 SNPs are greater than .05.
In Table 3, the haplotype analysis of CAC in rs3752826, rs2131431, and rs1873827 in the male group (χ2 = 25.744, P = 3.97E-07, OR = 0.478 [95% CI, 0.358-0.639]) and of ACT and CAC in rs3752826, rs2131431, and rs1873827 in the female group (for ACT, χ2 = 30.365, P = 3.67E-08, OR = 0.040 [95% CI, 0.007-0.218]; for CAC, χ2 = 16.874, P = 4.04E-05, OR = 0.597 [95% CI, 0.466-0.765]) showed they are protective factors for bipolar disorder. The haplotype analysis of CAT in the male group (χ2 = 19.874, P = 8.39E-06, OR = 2.314 [95% CI, 1.587-3.374]) and of AAC and CAT in the female group (for AAC, χ2 = 38.561, P = 5.47E-10, OR = 7.104 [95% CI, 3.471-14.540]; for CAT, χ2 = 25.497, P = 4.52E-07, OR = 2.076 [95% CI, 1.556-2.770]) showed they are risk factors for bipolar disorder.
DISCUSSION
Although no significant associations were shown between the 11 SNPs of YWHAE gene and bipolar disorder when we investigated male and female subjects collectively in our prior study,14 significant associations may arise when looking at these SNPs in the male and female samples separately. Thus, the main purpose of the current study was to investigate whether there is a gender-limited association between the YWHAE gene and bipolar disorder. We tested 11 SNPs of YWHAE gene between the bipolar disorder cases and controls. By the angle of both allele and genotype frequencies analysis, our results indicate that, in the male group, rs1873827 showed statistically significant differences between the 533 cases and 296 controls. Also in the male group, the CAC haplotype and CAT haplotype of rs3752826, rs2131431, and rs1873827 were positively associated with bipolar disorder. For the CAC haplotype, the OR value and the upper limit of 95% CI were less than 1, which indicates that CAC was a protective factor for bipolar disorder. For haplotype CAT, the OR value and the lower limit of 95% CI were greater than 1, which indicates that CAT was a risk factor for bipolar disorder. When we applied the same metric to the female group, the AAC haplotype and the CAT haplotype of rs3752826, rs2131431, and rs1873827 were positively associated with bipolar disorder, and they were both risk factors of the disease. On the other hand, the ACT and CAC were 2 protective factors for bipolar disorder. Therefore, the conclusion above shows that the combination of rs3752826, rs2131431, and rs1873827 may therefore play an important role in the development of bipolar disorder in both male and female groups. Compared with our prior study,14 the present one showed that, when analyzed separately by genders, the rs1873827 polymorphism, which was not significantly associated with bipolar disorder when analyzed in all cases and controls, was associated with the male group. The reason for this finding is that rs1873827 plays an important role in the male group with bipolar disorder, but not in the female group with bipolar disorder. Therefore, in our prior study, which analyzed subjects that were not divided into gender groups, the role of rs1873827 was masked. Also, since we did not subdivide bipolar disorder patients in our prior study, the associations shown with the haplotypes in the present study were not detected in the prior study.
In summary, by analyzing from the allele angle and the genotype angle, this study provides further evidence for the hypothesis that some susceptibility may be common to both schizophrenia and bipolar disorder, and its findings imply a putative, sex-dependent relationship between the YWHAE gene and bipolar disorder. The relatively weak association obtained in our study may result from the weak effect of the gene. However, analyzing the gene from the angle of haplotype, it is true that several important haplotypes may significantly affect bipolar disorder, in both the protective direction and the risk direction and in both the male group and the female group.
Certainly, there is an important limitation of our previous study and present study. The samples we used were all from Shanghai area. The results would be more convincing if we could use samples from all over the country or even from all over the world. Although caution is needed in drawing conclusions from the current data, our study and previous findings should encourage further investigation into YWHAE and its potential role in the etiology of neurologic and psychiatric diseases.
Author affiliations: Shanghai Key Laboratory for Prevention and Treatment of Bone and Joint Diseases with Integrated Chinese-Western Medicine, Shanghai Institute of Orthopaedics and Traumatology, Department of Orthopedics, Shanghai Ruijin Hospital, Shanghai Jiao Tong University School of Medicine (Dr Liu); Bio-X Institutes, Key Laboratory for the Genetics of Developmental and Neuropsychiatric Disorders (Ministry of Education), Shanghai Jiao Tong University (Drs Liu, Z-Q Li, J-Y Li, T Li, Wang, Y Li, Shi, and He, and Ms Feng); Shanghai Institute of Mental Health (Dr Xu); and Shanghai genomePilot Institutes for Genomics and Human Health and Institutes of Biomedical Sciences, Fudan University (Dr He), Shanghai, China.
Potential conflicts of interest: The authors declare no conflicts of interest.
Funding/support: This work was supported by grants from the 973 Program (2010CB529600) and the 863 Program (2012AA02A515) of the Chinese government, the National Key Technology Research and Development Program (2006BAI05A09, 2012BAI01B09), the National Nature Science Foundation of China (81121001, 81130022, 31000553), the Shanghai Municipal Commission of Science and Technology Program (09DJ1400601), and the Shanghai Leading Academic Discipline Project (B205).
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