Hiroto Nakano1, Emily Shuldiner2, Anne Hinks3, Marc Sudman4, Elaine Remmers5, Colleen Satorius6, Elizabeth Schmitz1, Victoria Arthur7, Patricia Woo8, Alexei Grom9, Dirk Foell10, John Bohnsack11, Marco Gattorno12, Seza Ozen13, Sampath Prahalad14, Rae Yeung15, Elizabeth Mellins2, Sheila Oliveira16, Jordi Antón17, Claudio Len18, Carol Lake19, Ly-Lan Bergeron20, Michelle Millwood21, Estefania de los santos21, Mariana Correia Marques22, Juvenile Arthritis Consortium for the Immunochip23, The Genomic Ascertainment Cohort Investigators24, INCHARGE Consortium25, Carl Langefeld26, Susan Thompson27, Wendy Thomson28 and Michael Ombrello1, 1National Institutes of Arthritis and Musculoskeletal and Skin Diseases (NIAMS), National Institutes of Health (NIH), Bethesda, MD, 2Stanford University, Stanford, CA, 3The University of Manchester, Manchester, United Kingdom, 4Cincinnati Children's Hospital Medical Center, Cincinnati, OH, 5National Human Genome Research Institute, Bethesda, MD, 6NHGRI, NIH, Bethesda, MD, 7Boston Children's Hospital, Boston, MA, 8University College London, London, United Kingdom, 9Divisions of Rheumatology, Cincinnati Children’s Hospital Medical Center, Cincinnati, OH, 10University Hospital Münster, Münster, Germany, 11University of Utah, Salt Lake City, UT, 12Pediatric Clinic and Rheumatology Unit, IRCCS Istituto Giannina Gaslini, Genoa, Italy, 13Hacettepe University Faculty of Medicine, Ankara, Turkey, 14Emory + Children's Pediatric Institute, Atlanta, GA, 15The Hospital for Sick Children, University of Toronto, Toronto, ON, Canada, 16Universidade Federal do Rio de Janeiro, Rio De Janeiro, Brazil, 17Pediatric Rheumatology Department. Hospital Sant Joan de Déu. Universitat de Barcelona, Esplugues de Llobregat, Spain, 18Universidade Federal de São Paulo, São Paulo, Brazil, 19NIH, Gaithersburg, MD, 20NIH/NIAMS, Vienna, VA, 21NIAMS, NIH, Bethesda, MD, 22National Institute of Arthritis and Musculoskeletal and Skin Diseases / Children`s National Hospital, Bethesda, MD, 23Juvenile Arthritis Consortium for the Immunochip, Bethesda, MD, 24The Genomic Ascertainment Cohort Investigators, Bethesda, MD, 25International Childhood Arthritis Genetics Consortium, Bethesda, MD, 26Wake Forest School of Medicine, Winston Salem, NC, 27Cincinnati Children's Hospital Medical Center/Univ of Cincinnati College of Medicine, Blue Ash, OH, 28Manchester Academic Health Science Centre, Manchester, United Kingdom
Background/Purpose: Systemic juvenile idiopathic arthritis (sJIA) is a rare inflammatory disease that causes spiking fever, skin rash, chronic arthritis, and inflammation of the heart and lungs. Despite recognition of excessive innate immune responses, the cause of sJIA is largely unknown. Genomic investigations are an important tool for identifying new disease-associated genes and pathways. To explore the genetic contribution to sJIA, we studied an international cohort of sJIA cases and matched controls with the Immunochip, a single nucleotide polymorphism (SNP) array that generates exceptionally dense genotyping at 186 loci of immunologic importance.
Methods: SNP genotyping was performed with Immunochip arrays in 889 subjects with ILAR-classified sJIA and 16,144 control subjects according to manufacturer’s protocols. Quality control operations (QC) were applied to remove poor quality samples/markers and to remove ancestral outliers. Imputation was performed with the Michigan Imputation Server. Haplotype analysis was performed with Haploview. Association testing was performed by logistic regression, corrected for sex and ancestry. Variant-expression relationships were examined in silico in paired DNA/RNA sequencing data from 1000 Genomes Project (1KG). Migration of fresh peripheral leukocytes was measured by flow cytometry-based transwell assay. Statistical analyses used Kruskal-Wallis test.
Results: SNP genotyping and QC yielded a final population of 579 sJIA cases and 12,930 control subjects. Association testing of an imputation-expanded SNPset identified a novel, highly significant susceptibility locus on chromosome 2. The strongest risk factor was a 124kb 6-SNP haplotype that contained the entire CXCR4 gene (OR 1.7; p=4.3E-10), encoding C-X-C chemokine receptor type 4. Homozygosity for the haplotype conferred an even greater risk of sJIA (OR 2.8). The sJIA risk haplotype correlated with high CXCR4 expression in B lymphoblasts from 1KG participants (p=4.0E-4). Because CXCR4 is important for the development, maturation and migration of many leukocyte populations, we evaluated the effect of the haplotype on leukocyte migration towards CXCL12 in 6 pairs of population control subjects with 0 and 2 copies of the risk haplotype. CD14+ monocytes and neutrophils from risk haplotype homozygotes displayed greater migration towards the CXCR4 ligand, CXCL12, than did monocytes from subjects without the risk haplotype. Finally, when we examined CD14+ monocyte RNAseq data from sJIA patients (GSE147608), expression of CXCR4 was higher in sJIA monocytes than in those from healthy subjects, regardless of disease activity (p=0.0009).
Conclusion: We report a novel association between sJIA and a high-expression CXCR4 haplotype. Homozygosity for this haplotype is nearly 3-fold greater in sJIA than in the control population. The risk haplotype leads to increased migration of CD14+ monocytes and neutrophils from healthy subjects. The relevance of this finding is amplified by the observation that CXCR4 expression is increased in CD14+ monocytes from both active and inactive sJIA patients. This suggests that increased CXCR4 expression and signaling may be a genetically-encoded, intrinsic characteristic of sJIA.
Disclosures: H. Nakano, None; E. Shuldiner, None; A. Hinks, None; M. Sudman, None; E. Remmers, None; C. Satorius, None; E. Schmitz, None; V. Arthur, None; P. Woo, None; A. Grom, Sobi, Novartis; D. Foell, Novartis, Sobi, Boehringer, Novartis, Sobi; J. Bohnsack, None; M. Gattorno, None; S. Ozen, None; S. Prahalad, Novartis; R. Yeung, None; E. Mellins, GlaxoSmithKline, Genentech, Codexis; S. Oliveira, None; J. Antón, None; C. Len, None; C. Lake, None; L. Bergeron, None; M. Millwood, None; E. de los santos, None; M. Correia Marques, None; J. for the Immunochip, None; T. Investigators, None; I. Consortium, None; C. Langefeld, None; S. Thompson, None; W. Thomson, None; M. Ombrello, None.
