Genome-Wide Association Identifies a Common Variant in the Reelin Gene That Increases the Risk of Schizophrenia Only in Women Sagiv Shifman 1*¤ , Martina Johannesson 1 , Michal Bronstein 2 , Sam X. Chen 3,4 , David A. Collier 5 , Nicholas J. Craddock 6 , Kenneth S. Kendler 3,4 , Tao Li 5,7,8 , Michael O’Donovan 6 , F. Anthony O’Neill 9 , Michael J. Owen 6 , Dermot Walsh 10 , Daniel R. Weinberger 11 , Cuie Sun 3,4 , Jonathan Flint 1 , Ariel Darvasi 2 1 Wellcome Trust Centre for Human Genetics, University of Oxford, Oxford, United Kindgdom, 2 Department of Genetics, The Institute of Life Sciences, The Hebrew University of Jerusalem, Jerusalem, Israel, 3 Department of Psychiatry, Virginia Commonwealth University, Richmond, Virginia, United States of America, 4 Virginia Institute for Psychiatric and Behavior Genetics, Virginia Commonwealth University, Richmond, Virginia, United States of America, 5 Social, Genetic and Developmental Psychiatry Centre, Institute of Psychiatry, King’s College London, London, United Kingdom, 6 Department of Psychological Medicine, School of Medicine, Cardiff University, Cardiff, United Kingdom, 7 Psychiatric Laboratory and Department of Psychiatry, West China Hospital, Sichuan University, The People’s Republic of China, 8 State Key Laboratory of Biotherapy, West China Hospital, Sichuan University, The People’s Republic of China, 9 The Department of Psychiatry, The Queens University, Belfast, Northern Ireland, 10 The Health Research Board, Dublin, Ireland, 11 Clinical Brain Disorders Branch, Genes, Cognition, and Psychosis Program, Intramural Research Program, National Institute of Mental Health, National Institutes of Health (NIH), United States Department of Health and Human Services, Bethesda, Maryland, United States of America Sex differences in schizophrenia are well known, but their genetic basis has not been identified. We performed a genome-wide association scan for schizophrenia in an Ashkenazi Jewish population using DNA pooling. We found a female-specific association with rs7341475, a SNP in the fourth intron of the reelin (RELN) gene (p ¼ 2.9 3 10 5 in women), with a significant gene-sex effect (p ¼ 1.8 3 10 4 ). We studied rs7341475 in four additional populations, totaling 2,274 cases and 4,401 controls. A significant effect was observed only in women, replicating the initial result (p ¼ 2.1 3 10 3 in women; p ¼ 4.2 3 10 3 for gene-sex interaction). Based on all populations the estimated relative risk of women carrying the common genotype is 1.58 (p ¼ 8.8 3 10 7 ; p ¼ 1.6 3 10 5 for gene-sex interaction). The female- specific association between RELN and schizophrenia is one of the few examples of a replicated sex-specific genetic association in any disease. Citation: Shifman S, Johannesson M, Bronstein M, Chen SX, Collier DA, et al. (2008) Genome-wide association identifies a common variant in the reelin gene that increases the risk of schizophrenia only in women. PLoS Genet 4(2): e28. doi:10.1371/journal.pgen.0040028 Introduction Schizophrenia (181500) is a common psychiatric disorder of unknown aetiology. Individual twin studies and meta- analyses of twin studies [1] estimate that the heritability of schizophrenia is approximately 80%. Analysis of family, adoption and twin data indicate that inheritance acts in a complex fashion, in combination with the environment, to mediate the risk of developing the illness [2]. However, despite the relatively large heritability of schizophrenia, efforts to identify the molecular risk factors have so far yielded equivocal results (reviewed in [3]). Sex differences in the risk of a disorder can provide clues about its pathogenesis. For schizophrenia, the age of onset, premorbid functioning, symptomatic characteristics, and course of illness differ significantly between men and women [4]. Two systematic reviews have demonstrated a sex differ- ence in the risk of developing schizophrenia [5,6]; both studies report that the male to female risk ratio is 1.4. Sex- specific associations with schizophrenia have previously been reported for a number of loci [7–11], but the robustness of these claims is open to doubt; results have yet to be corroborated [8–10] or replication has not been found with the same single nucleotide polymorphism (SNP) in the same direction in the same sex (e.g. [7,11]). This difficulty has afflicted attempts to establish sex-specific association in other diseases. An empirical assessment of 432 published sex differences in genetic association studies for different conditions found a single valid interaction that was consis- tently replicated in at least two other studies [12]. In the present study, we carried out a genome-wide association study using DNA pools of cases and controls constructed separately for men and women to allow the identification of sex-specific effects. Several studies have shown that DNA pooling detects the most promising loci with considerable savings in time and costs [13–18]. We previously scanned a three Mb region spanning the 22q11 microdeletion for association with schizophrenia using DNA pools. Our previous study [7,19] showed that the pools are representative of the allele frequencies in the sample and are adequate for Editor: Greg Gibson, North Carolina State University, United States of America Received October 5, 2007; Accepted December 17, 2007; Published February 15, 2008 Copyright: Ó 2008 Shifman et al. This is an open-access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited. Abbreviations: CEU, Utah residents with ancestry from northern and western Europe; LD, linkage disequilibrium; MAF, minor allele frequency; OR, odds ratio; SNP, single nucleotide polymorphism * To whom correspondence should be addressed. E-mail: sagiv@vms.huji.ac.il ¤ Current address: Department of Genetics, The Institute of Life Sciences, The Hebrew University of Jerusalem, Jerusalem, Israel PLoS Genetics | www.plosgenetics.org February 2008 | Volume 4 | Issue 2 | e28 0001