University of Groningen Mapping of Gene Expression Reveals CYP 27 A 1 as a Susceptibility Gene for Sporadic

Amyotrophic lateral sclerosis (ALS) is a progressive, neurodegenerative disease characterized by loss of upper and lower motor neurons. ALS is considered to be a complex trait and genome-wide association studies (GWAS) have implicated a few susceptibility loci. However, many more causal loci remain to be discovered. Since it has been shown that genetic variants associated with complex traits are more likely to be eQTLs than frequency-matched variants from GWAS platforms, we conducted a two-stage genome-wide screening for eQTLs associated with ALS. In addition, we applied an eQTL analysis to finemap association loci. Expression profiles using peripheral blood of 323 sporadic ALS patients and 413 controls were mapped to genome-wide genotyping data. Subsequently, data from a two-stage GWAS (3,568 patients and 10,163 controls) were used to prioritize eQTLs identified in the first stage (162 ALS, 207 controls). These prioritized eQTLs were carried forward to the second sample with both gene-expression and genotyping data (161 ALS, 206 controls). Replicated eQTL SNPs were then tested for association in the second-stage GWAS data to find SNPs associated with disease, that survived correction for multiple testing. We thus identified twelve cis eQTLs with nominally significant associations in the second-stage GWAS data. Eight SNP-transcript pairs of highest significance (lowest p = 1.27610) withstood multiple-testing correction in the second stage and modulated CYP27A1 gene expression. Additionally, we show that C9orf72 appears to be the only gene in the 9p21.2 locus that is regulated in cis, showing the potential of this approach in identifying causative genes in association loci in ALS. This study has identified candidate genes for sporadic ALS, most notably CYP27A1. Mutations in CYP27A1 are causal to cerebrotendinous xanthomatosis which can present as a clinical mimic of ALS with progressive upper motor neuron loss, making it a plausible susceptibility gene for ALS. Citation: Diekstra FP, Saris CGJ, van Rheenen W, Franke L, Jansen RC, et al. (2012) Mapping of Gene Expression Reveals CYP27A1 as a Susceptibility Gene for Sporadic ALS. PLoS ONE 7(4): e35333. doi:10.1371/journal.pone. 0035333 Editor: Marcel P. van der Brug, Genentech, United States of America Received December 20, 2011; Accepted March 13, 2012; Published April 11, 2012 Copyright: 2012 Diekstra 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. Funding: This work was supported by the Prinses Beatrix Fonds (Kersten Foundation); VSB fonds; The Netherlands ALS Foundation and J.R. van Dijk; and the Adessium Foundation to [LHB]. JHV is supported by the Brain Foundation of The Netherlands; and the Thierry Latran Foundation. The GWA study was funded by the Netherlands Organization of Scientific Research NWO Investments [grant numbers 175.010. 2005.011, 911-03-012]; the Research Institute for Diseases in the Elderly (014-93-015; RIDE); and the Netherlands Genomics Initiative (NGI)/Netherlands Organisation for Scientific Research (NWO) [project number 050-060-810]. In addition, the research leading to these results has received funding from the European Community’s Health Seventh Framework Programme (FP7/2007-2013) [grant agreement number 259867]. SH is supported by National Institutes of Health [grant numbers IU19A1063603-01, 5P30CA016042-28, P50CA092131, and DK072206]. The Rotterdam Study is funded by Erasmus Medical Center and Erasmus University, Rotterdam; Netherlands Organization for the Health Research and Development (ZonMw); the Research Institute for Diseases in the Elderly (RIDE); the Ministry of Education, Culture and Science; the Ministry for Health, Welfare and Sports; the European Commission (DG XII); and the Municipality of Rotterdam. The Irish study was funded by The Muscular Dystrophy Association (USA); The Health Research Board of Ireland; The Irish Neurological Association Travel Award; and The Irish Motor Neuron Disease Research Foundation. In Sweden, this project was supported by the Swedish Brain Research Foundation; the Hållstens Research Foundation; the Swedish Medical Society; the Björklund Foundation for ALS Research; and the Swedish Association for the Neurologically Disabled to [PMA]. WR was supported by grants from the University of Leuven (Methusalem); and the Interuniversity Attraction Poles program P6/43 of the Belgian Federal Science Policy Office. In France, this study was funded by the Association pour la Recherche sur la SLA; and the Association Réseau SLA Ile de France. Support was also provided by the ALS Therapy Alliance; Project ALS; the Angel Fund; the Pierre L. de Bourgknecht ALS Research Foundation; the Al-Athel ALS Research Foundation; the ALS Family Charitable Foundation and the National Institute of Neurological Disorders and Stroke [NS050557]. ’’ The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript. PLoS ONE | www.plosone. org 1 April 2012 | Volume 7 | Issue 4 | e35333 Competing Interests: The authors have declared that no competing interests exist. * E-mail: j.h. veldink@umcutrecht.nl . These authors contributed equally to this work.