Abstract
Background
Susceptibility genes for migraine, despite it being a highly prevalent and disabling neurological disorder, have not been analyzed in Asians by genome-wide association study (GWAS).
Methods
We conducted a two-stage case-control GWAS to identify susceptibility genes for migraine without aura in Han Chinese residing in Taiwan. In the discovery stage, we genotyped 1005 clinic-based Taiwanese migraine patients and 1053 population-based sex-matched controls using Axiom Genome-Wide CHB Array. In the replication stage, we genotyped 27 single-nucleotide polymorphisms with
Results
We identified a novel susceptibility locus (rs655484 in
Conclusion
The present study is the first migraine GWAS conducted in Han-Chinese and Asians. The newly identified susceptibility genes have potential implications in migraine pathogenesis.
Introduction
As the most common and disabling complex neurological disorder in humans, migraine is characterized by recurrent throbbing headache that may be associated with nausea, vomiting, photophobia, or phonophobia (1,2). The global one-year prevalence of migraine is 14.6% (1). In Asians, this prevalence is 9.1% (3). Clinically, migraine can be classified into migraine with or without aura, according to the International Classification of Headache Disorders (ICHD) (4,5). Migraine with aura accounts for approximately one-third of migraine cases in Western countries, but only about one-tenth of cases in Asians (3). Migraine-associated photophobia is also less commonly noted in Asian patients with migraine (6,7). These differences suggest that the genetic contribution of migraine pathogenesis could vary across different ethnic groups.
Recently, genome-wide association studies (GWASs) in Caucasians have identified common genetic variants associated with migraine with or without aura (8–12). Collectively, 38 genetic variants have been identified (8–12). Three of these variants, in
The purpose of this study was to report the first GWAS of migraine in Asians. We performed a two-stage case-control GWAS using clinic-based migraine patients and population-based controls as discovery and validation cohorts. We sought to identify susceptibility genes for migraine without aura in Han Chinese residing in Taiwan.
Materials and methods
Ethics
This study was approved by the Institutional Review Boards of Taipei Veterans General Hospital, National Yang-Ming University, and Academia Sinica, Taiwan. Written informed consent was obtained from each participant after full explanation of the study objectives and procedures. All clinical investigations were conducted according to the principles expressed in the Declaration of Helsinki. All collected information was de-identified before statistical data analysis. The corresponding authors had full access to all of the data in the study and had final responsibility for the decision to submit for publication.
Study participants and data collection
This study was a two-stage case-control GWAS, including a discovery cohort and a replication cohort. The initial significant findings of the discovery cohort were validated in the replication cohort, and a combined analysis of both cohorts was employed to examine the significance of the validated SNPs. For this study, including the discovery and replication cohorts of the case-control GWAS, we enrolled patients with migraine from headache or neurologic clinics in Taiwan. We recruited 85% of subjects from a single tertiary medical center (Taipei Veterans General Hospital) (Supplementary Figure 1). The discovery and replication cohorts were recruited based on the time they entered the study. Subjects who were recruited before 2012 were included in the discovery cohort and subjects recruited after that were assigned to the replication cohort.
All participants filled out a structured questionnaire that included questions on personal information, medical history, and headache history. Participants were interviewed, with their questionnaires and medical records reviewed simultaneously, by board-certified neurologists who were experienced in headache diagnosis. Diagnosis of migraine was made according to the criteria proposed in the ICHD, 2nd edition (4).
Some categories of patients were excluded from this study. First, patients with migraine with aura were excluded for two reasons: (a) The low prevalence of aura in Taiwanese migraine patients (10%) made it difficult to achieve an adequate sample size for acceptable statistical power; (b) a meta-analysis of GWASs found that with the same sample size, the power to identify risk alleles for migraine without aura was higher than that for migraine with aura (10). Second, patients with “age at onset > 35 years old” (16) were excluded. This condition was set to enrich the genetic component, because migraine is a complex disease that is subject to environmental influences (only ∼ 50% heritability). Third, after employing questionnaires to quasi-quantify the severity of psychological disturbance, patients with a Beck Depression Inventory (BDI) score greater than 20 were excluded. This criterion was used because genetic risk score analysis showed that migraine with and without comorbid depression might be genetically different disorders (17). Fourth, patients were excluded if they had a history of head injury. Fifth, Taiwanese aborigines were excluded to ensure that all participants were of Han Chinese descent.
All clinical information was uploaded to the digitalized Clinical Study Information System for computation. Control subjects in the discovery and replication cohorts of the case-control GWAS were obtained from a representative genomic sample randomly selected from The Cell Bank and Genetic Database of Non-Aboriginal Taiwanese (18). Subjects with a history of migraine were excluded by using a validated pre-enrollment screening questionnaire. The control groups were age- and sex-matched to the patient groups in both discovery and replication cohorts. The baseline characteristics of participants in both cohorts were analyzed.
Genotyping in the discovery cohort
In the discovery stage, we genotyped 642,832 single-nucleotide polymorphisms (SNPs) using the Affymetrix Axiom Genome-Wide CHB 1 Array Plate, which has the highest coverage of genome-wide common variants for Han Chinese, at the National Center for Genomics Medicine, Academia Sinica, Taiwan . SNP genotypes were called using the Axiom GT1 algorithm. Quality control (QC) criteria for SNPs were applied to exclude SNPs if they (a) were monomorphic in both cases and controls, (b) had a total call rate of less than 95% in cases and controls combined, (c) had a minor allele frequency of less than 5%
Heterozygosity of SNPs on the X chromosome was used to verify the sex of the samples. PLINK version 1.07 software (19) was used to identify samples with genetic relatedness, indicating that they were from the same individual (or monozygotic twins) or from first, second or third degree relatives. These determinations were made on the basis of evidence for cryptic relatedness from identity-by-descent status (pi-hat cutoff of 0.125). After QC filtering, 590,945 autosomal SNPs in 1005 cases and 1053 controls were retained for analysis.
Genotyping in the replication cohort
We selected SNPs with a trend
Genotype imputation analysis
We conducted a genotype imputation analysis in the discovery cohort using the 1000 Genomes Phase 3 reference data (20) and IMPUTE2 as implemented (21–23). Well-imputed SNPs (info score > 0.4) were retained followed by systematic QC, as described above (24).
Statistical analysis
Association analyses were carried out by comparing allele/genotype/haplotype frequencies between migraine cases and controls using six single-point methods: Genotype, allele-type, and Cochran–Armitage trend tests along with tests considering additive, dominant, and recessive models. The distribution of expected
Detection of possible population stratification was carried out by using principal component analysis (PCA) as implemented in EIGENSTRAT to infer continuous axes of genetic variation (Supplementary Figure 2) . We adjusted for potential genetic heterogeneity by incorporating the first two or first 10 PCs in the logistic regression tests of association with migraine without aura. Joint analysis was conducted by combining data from the discovery and validation samples of the case-control GWAS.
Results
Study participants
Baseline characteristics of participants.
Association analysis of GWAS
In the first stage, we genotyped 1005 cases and 1053 controls using the Affymetrix Axiom Genome-Wide CHB 1 Array Plate (Figure 1). After applying stringent QC criteria, we obtained 590,945 (91.93%) SNPs with an average call rate of 99.66% ± 0.43%. The value of the genomic inflation factor was 1.037, suggesting that there was little evidence for population stratification in our study sample (Figure 2). PCA showed no outliers (Supplementary Figure 2).
Manhattan plot for migraine association. Manhattan plot of the discovery genome-wide association analysis of 1005 cases and 1053 controls. The Quantile-quantile plot of results from the Cochran-Mantel-Haenszel analysis. Red line represents the distribution of 

Association results for migraine without aura in Han Chinese resided in Taiwan.
Abbreviations: SNP, single nucleotide polymorphism; Chr, chromosome; OR, odds ratio for risk allele; CI, confidence interval; PC, principal component. Stage 1 (GWAS) included 1005 cases and 1053 controls. Stage 2 (replication stage) included 1120 cases and 604 controls.

Regional plots of association signals. Regional plots for two newly identified loci associated with migraine in the discovery cohort. Each regional plot shows the chromosomal position (GRCh37/hg19) of SNPs in the specific region against –log10
In the discovery dataset, rs655484 in
The second most significant SNP in the discovery cohort was rs3781545 in
Also significantly associated with migraine in the discovery cohort were two other SNPs, rs10803531 in G protein-coupled receptor 39 (
Replications of genetic variants identified in Caucasian GWASs
We examined whether SNPs that have been repetitively found to be associated with migraine risk in Caucasians (i.e.,
Discussion
To the best of our knowledge, this report describes the results of the first migraine GWAS to be performed in an Asian population. We identified two novel migraine susceptibility genes,
We found that rs3781545 in
GPR39 is a G protein coupled metabotropic Zn2+ receptor, and widely expressed in the brain (39). The role of GPR39 in migraine pathogenesis has not been reported. GPR39 is associated with the zinc-related changes in the level of cAMP response element-binding protein (CREB) and brain-derived neurotrophic factor (BDNF), and
Our study has several implications. First, our findings provide genetic evidences to support prevailing theories of migraine pathogenesis, including glutamatergic neurotransmission, altered nociception, and oxidative stress (10,28,29). The novel genes that we identified all have been implicated in regulating glutamatergic/GABAergic homeostasis.
Our study has several limitations. First, only common variants were included from the GWAS results in this study. Further investigations would be required to look at rare variants, as they are likely to have the larger effect size, and to use predictive software tools to obtain an indication of whether they are damaging or not. Second, the Axiom Genome-Wide CHB Array we used in our discovery cohort did not contain the SNPs for
In this study, we identified novel genetic variants and replicated two previously identified variants for migraine susceptibility. Functional studies are mandatory to dissect the molecular mechanisms and to identify potential therapeutic targets for this complex neurological disorder.
Clinical implications
Two novel susceptibility genes, DLG2 is a membrane-associated guanylate kinase responsible for glutamatergic neurotransmission, supporting the theory of neuronal hyperexcitability. GFRA1 is a receptor of glial-derived neurotrophic factor expressed in CGRP-containing trigeminal neurons, suggesting its importance in modulating the trigeminovascular system. Successful replication of
Footnotes
Acknowledgements
We wish to thank all individuals in this study for their generous participation. We thank the National Center for Genome Medicine of Taiwan for the technical/bioinformatics/statistics support.
Declaration of conflicting interests
The authors declared no potential conflicts of interest with respect to the research, authorship, and/or publication of this article.
Funding
The authors disclosed receipt of the following financial support for the research, authorship, and/or publication of this article: This work was supported by the Ministry of Education, Aim for the Top University Plan (to SWJ and LSK); Brain Research Center, National Yang-Ming University (to SWJ and LSK); Taipei Veterans General Hospital [V100E6-001, V101E7-003, V102E9-001, V103E9-006, V104E9-001, V105E9-001-MY2-1] (to SWJ); Ministry of Science and Technology of Taiwan [MOST 104-2314-B-010-015-MY2, and MOST 103-2321-B-010-017-] (to SWJ); Ministry of Science and Technology support for the Center for Dynamical Biomarkers and Translational Medicine, National Central University, Taiwan [MOST 103-2911-I-008-001] (to SWJ); National Center for Genome Medicine of the National Core Facility Program for Biotechnology, Ministry of Science and Technology, Taiwan; Institute of Biomedical Sciences, Academia Sinica [Grant No. IBMS-CRC103-P04, 104-2314-B-001-003-] (to CSJF); Taiwan Han Chinese Cell and Genome Bank of Academia Sinica; Translational Resource Center for Genomic Medicine of National Research Program for Biopharmaceuticals (NRPB), Taiwan; and Ministry of Health and Welfare, Taiwan [MOHW 103-TDU-B-211-113-003, MOHW 104-TDU-B-211-113-003, MOHW 105-TDU-B-211-113-003] (to SJW). The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.
References
Supplementary Material
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