Myelin Basic Protein as a Novel Genetic Risk Factor in Rheumatoid Arthritis—A Genome-Wide Study Combined with Immunological Analyses

Chikashi Terao,Koichiro Ohmura,Ryo Yamada,Simon Heath,Gora Diop,Masaki Katayama,Natsuki Yamamoto,Ivo Gut,Meiko Takahashi,Tsuneyo Mimori,Mark Lathrop,Fumihiko Matsuda,Toshiaki Manabe,Reiko Shinkura,Yoshinobu Toda,Inga Melchers,Masakazu Shimizu,Mitsunori Kokubo

doi:10.1371/journal.pone.0020457

Abstract

Rheumatoid arthritis (RA) is a major cause of adult chronic inflammatory arthritis and a typical complex trait. Although several genetic determinants have been identified, they account for only a part of the genetic susceptibility. We conducted a genome-wide association study of RA in Japanese using 225,079 SNPs genotyped in 990 cases and 1,236 controls from two independent collections (658 cases and 934 controls in collection1; 332 cases and 302 controls in collection2), followed by replication studies in two additional collections (874 cases and 855 controls in collection3; 1,264 cases and 948 controls in collection4). SNPs showing p<0.005 in the first two collections and p<10−4 by meta-analysis were further genotyped in the latter two collections. A novel risk variant, rs2000811, in intron2 of the myelin basic protein (MBP) at chromosome 18q23 showed strong association with RA (p = 2.7×10−8, OR 1.23, 95% CI: 1.14–1.32). The transcription of MBP was significantly elevated with the risk allele compared to the alternative allele (p<0.001). We also established by immunohistochemistry that MBP was expressed in the synovial lining layer of RA patients, the main target of inflammation in the disease. Circulating autoantibody against MBP derived from human brain was quantified by ELISA between patients with RA, other connective tissue diseases and healthy controls. As a result, the titer of anti-MBP antibody was markedly higher in plasma of RA patients compared to healthy controls (p<0.001) and patients with other connective tissue disorders (p<0.001). ELISA experiment using citrullinated recombinant MBP revealed that a large fraction of anti-MBP antibody in RA patients recognized citrullinated MBP. This is the first report of a genetic study in RA implicating MBP as a potential autoantigen and its involvement in pathogenesis of the disease.

Highlights

Rheumatoid arthritis (RA) is the most common cause of adult inflammatory arthritis, affecting 0.5–1% of the adult population worldwide, and is associated with joint pain, dysfunction and deformity
For 225,079 markers that were common between the arrays and fulfilled our inclusion criteria, we found no evidence of population stratification between cases and controls
A genome scan of 225,079 SNPs in two DNA collections of RA patients followed by replication in two additional collections led to identification of a novel risk variant, rs2000811 (p = 2.761028, OR 1.23, 95% CI: 1.14–1.32), in the second intron of the myelin basic protein (MBP) gene at chromosome 18q23

Summary

Introduction

Rheumatoid arthritis (RA) is the most common cause of adult inflammatory arthritis, affecting 0.5–1% of the adult population worldwide, and is associated with joint pain, dysfunction and deformity. Large-scale genetic analyses including genome-wide association (GWA) studies have shown that more than 20 genes such as PTPN22, TRAF1/C5, CD40, and TNFAIP3 are associated with RA in populations of European descent [4,5,6,7,8,9,10,11,12]. The size of DNA collections used for GWA studies is much larger in European populations than in Japanese, suggesting the existence of unknown genetic factors in Japanese [12,17]. The collections from two centers, totaling 990 cases and 1,241 controls, were characterized with genome-wide SNP arrays, and the data were analyzed to identify potential disease-associated loci. SNPs at these loci were examined in the two remaining collections, totaling 2,138 cases and 1,803 controls

Methods

Results

Conclusion