Evidence for Genetic Overlap Between Schizophrenia and Age at First Birth in Women

IMPORTANCE: A recently published study of national data by McGrath et al in 2014 showed increased risk of schizophrenia (SCZ) in offspring associated with both early and delayed parental age, consistent with a U-shaped relationship. However, it remains unclear if the risk to the child is due to psychosocial factors associated with parental age or if those at higher risk for SCZ tend to have children at an earlier or later age. OBJECTIVE: To determine if there is a genetic association between SCZ and age at first birth (AFB) using genetically informative but independently ascertained data sets. DESIGN, SETTING, AND PARTICIPANTS: This investigation used multiple independent genome-wide association study data sets. The SCZ sample comprised 18?957 SCZ cases and 22?673 controls in a genome-wide association study from the second phase of the Psychiatric Genomics Consortium, and the AFB sample comprised 12?247 genotyped women measured for AFB from the following 4 community cohorts: Estonia (Estonian Genome Center Biobank, University of Tartu), the Netherlands (LifeLines Cohort Study), Sweden (Swedish Twin Registry), and the United Kingdom (TwinsUK). Schizophrenia genetic risk for each woman in the AFB community sample was estimated using genetic effects inferred from the SCZ genome-wide association study. MAIN OUTCOMES AND MEASURES: We tested if SCZ genetic risk was a significant predictor of response variables based on published polynomial functions that described the relationship between maternal age and SCZ risk in offspring in Denmark. We substituted AFB for maternal age in these functions, one of which was corrected for the age of the father, and found that the fit was superior for the model without adjustment for the father's age. RESULTS: We observed a U-shaped relationship between SCZ risk and AFB in the community cohorts, consistent with the previously reported relationship between SCZ risk in offspring and maternal age when not adjusted for the age of the father. We confirmed that SCZ risk profile scores significantly predicted the response variables (coefficient of determination R2?=?1.1E-03, P?=?4.1E-04), reflecting the published relationship between maternal age and SCZ risk in offspring by McGrath et al in 2014. CONCLUSIONS AND RELEVANCE: This study provides evidence for a significant overlap between genetic factors associated with risk of SCZ and genetic factors associated with AFB. It has been reported that SCZ risk associated with increased maternal age is explained by the age of the father and that de novo mutations that occur more frequently in the germline of older men are the underlying causal mechanism. This explanation may need to be revised if, as suggested herein and if replicated in future studies, there is also increased genetic risk of SCZ in older mothers. This research is supported by grants 613602, 1047956, 1078901, 1080157, 1087889, and 1067795 from the Australian National Health and Medical Research Council and by grants DE130100614 and DP160102126 from the Australian Research Council. Primary analyses of the SchizophreniaWorking Group of the Psychiatric Genomics Consortium data were conducted on the Genetic Cluster Computer (http://www .geneticcluster.org) hosted by SURFsara and supported by grant NOW480-05-003 from the Netherlands Scientific Organization, along with a supplement from the Dutch Brain Foundation and the Vrije Universitiet Amsterdam. TwinsUK was funded by theWellcome Trust, by grant FP7/2007-2013 from the European Community’s Seventh Framework Programme, and by support from the National Institute for Health Research–funded BioResource, Clinical Research Facility, and Biomedical Research Centre based at Guy’s and St Thomas’ National Health Service Foundation Trust in partnership with King’s College London, and single-nucleotide polymorphism genotyping was performed by theWellcome Trust Sanger Institute and National Eye Institute via the National Institute for Health/Center for Inherited Disease Research. Estonian Genome Center Biobank, University of Tartu, received targeted financing by grant IUT20-60 from the Estonian Research Council, Center of Excellence in Genomics, and University of Tartu, and data analyses were carried out in part in the High Performance Computing Center of the University of Tartu. The Swedish Twin Registry is supported by Karolinska Institutet. Mr Tropf received funding from sciencestarter.de for a research visit to The University of Queensland. The research leading to these results received funding from the European Research Council via an ERC Consolidator Grant SOCIOGENOME (grant 615603 awarded to Dr Mills [http://www.sociogenome.com]).