National Institutes of Health/ Children`s National Hospital Bethesda, MD, United States
Mariana Correia Marques1, Danielle Rubin2, Emily Shuldiner2, Elizabeth Schmitz2, Elizabeth Baskin2, Andrew Patt3, Alexei Grom4, Dirk Foell5, Marco Gattorno6, John Bohnsack7, Rae Yeung8, Sampath Prahalad9, Elizabeth Mellins10, Jordi Antón11, Claudio Len12, Sheila Oliveira13, Patricia Woo14, Seza Ozen15, INCHARGE Consortium16 and Michael Ombrello17, 1National Institute of Arthritis and Musculoskeletal and Skin Diseases / Children`s National Hospital, Bethesda, MD, 2National Institute of Arthritis and Musculoskeletal and Skin Diseases, Bethesda, MD, 3National Center for Advancing Translational Sciences, Bethesda, MD, 4Divisions of Rheumatology, Cincinnati Children’s Hospital Medical Center, Cincinnati, OH, 5University Hospital Münster, Münster, Germany, 6Pediatric Clinic and Rheumatology Unit, IRCCS Istituto Giannina Gaslini, Genoa, Italy, 7University of Utah, Salt Lake City, UT, 8The Hospital for Sick Children, University of Toronto, Toronto, ON, Canada, 9Emory + Children's Pediatric Institute, Atlanta, GA, 10Stanford University, Stanford, CA, 11Pediatric Rheumatology Department. Hospital Sant Joan de Déu. Universitat de Barcelona, Esplugues de Llobregat, Spain, 12Universidade Federal de São Paulo, São Paulo, Brazil, 13Universidade Federal do Rio de Janeiro, Rio De Janeiro, Brazil, 14University College London, London, United Kingdom, 15Hacettepe University Faculty of Medicine, Ankara, Turkey, 16International Childhood Arthritis Genetics Consortium, Bethesda, MD, 17National Institutes of Arthritis and Musculoskeletal and Skin Diseases (NIAMS), National Institutes of Health (NIH), Bethesda, MD
Background/Purpose: Systemic juvenile idiopathic arthritis (sJIA) is a genetically complex inflammatory condition. It can be marked by severe systemic inflammation that resembles the hereditary periodic fever syndromes (HPF). Sometimes that inflammation leads to macrophage activation syndrome (MAS), a secondary form of hemophagocytic lymphohistiocytosis (HLH). To date, studies have attempted to identify whether variants in HPF and familial HLH (fHLH) genes contribute to the pathophysiology of sJIA; however, they lacked sufficient statistical power to reach generalizable conclusions. Our goal was to determine whether rare variation in these genes contributes to the risk of developing sJIA.
Methods: Targeted sequencing of HPF (MEFV, MVK, NLRP12, NLRP3, NOD2, PSTPIP1, TNFRSF1A) and fHLH (LYST, PRF1, RAB27A, STX11, STXBP2, UNC13D) genes was performed in sJIA cases and control subjects from the International Childhood Arthritis Genetics Consortium cohort using Illumina Nextera Custom Capture Assays and Illumina sequencers. Sequence reads were aligned to human genome assembly hg19 with the Burrows-Wheeler Aligner. Data processing and quality control were performed using the Genome Analysis Toolkit. Variants were filtered to retain rare (minor allele frequency < 0.01), protein-altering variation that mapped to Ensembl canonical transcripts. The distribution of rare variants among sJIA cases was compared to the distribution among INCHARGE healthy controls or simulated data from the 33,370 Non-Finnish European (NFE) reference subjects from the Exome Aggregation Consortium (ExAC) using rare variant association testing (RVT). RVT was performed in R using the data-adaptive sum test and the sequence kernel association test. Significance was evaluated at a threshold of p < 0.05 after 100,000 permutations.
Results: Targeted sequencing was performed in 525 sJIA cases and 366 control subjects. Patients were excluded for meeting genetic criteria for HPF (n=4) or fHLH (n=2), and if their ancestry was dissimilar from the rest of the cohort by principal component analysis (39 cases, 1 control). Sequencing of the remining 480 sJIA cases identified 78 rare fHLH gene variants and 62 rare HPF gene variants. RVT comparing the distribution of rare variants of sJIA cases with that of the ExAC NFE population revealed significant rare variant associations between sJIA and LYST, STXBP2, UNC13D and MEFV. We also discovered recurrent, ultra-rare mutations of STXBP2, UNC13D, and MEFV among the sJIA cohort, including several that were not observed in the ExAC population. A sub-analysis of 123 sJIA cases with known MAS status (32 with MAS, 91 without MAS) identified a significant association between rare variation of UNC13D and the development of MAS in sJIA (SKAT p=0.024).
Conclusion: The observations of this study connect HPF and fHLH genes to the pathophysiology of sJIA. These results highlight the potential value of studying rare genetic variation in sJIA. To expand this approach, we have established a collaborative infrastructure to perform an exome sequencing-based study of rare variation across all protein-coding genes in sJIA.
Disclosures: M. Correia Marques, None; D. Rubin, None; E. Shuldiner, None; E. Schmitz, None; E. Baskin, None; A. Patt, None; A. Grom, Sobi, Novartis; D. Foell, Novartis, Sobi, Boehringer, Novartis, Sobi; M. Gattorno, None; J. Bohnsack, None; R. Yeung, None; S. Prahalad, Novartis; E. Mellins, GlaxoSmithKline, Genentech, Codexis; J. Antón, None; C. Len, None; S. Oliveira, None; P. Woo, None; S. Ozen, None; I. Consortium, None; M. Ombrello, None.
