Rheumatoid arthritis: Disease or syndrome?

Abstract

Rheumatoid arthritis (RA) has been described in the medical literature for over two hundred years, but its etiology remains unknown. RA displays phenotypic heterogeneity, and it is a relatively prevalent clinical entity: it affects approximately 1% of the population, resulting in enormous pathologic sequelae. Earlier studies targeting the cause(s) of RA suggested potential infectious involvement, whereas more recent reports have focused on a genetic origin of the disease. However, neither infection nor genetics, nor any other single factor is currently accepted as causative of RA. In this article we review studies relating to the etiology of RA, and those of several related matters, and we conclude that the literature indeed does provide insight into the causes underlying the initiation of RA pathogenesis. Briefly, given the remarkable phenotypic variation of RA, especially in its early stages, as well as a number of other characteristics of the condition, we contend that RA is not a discrete clinical entity with a single etiological source. Rather, we argue that it represents a common clinical endpoint for various starting points, each of which is largely guided by as yet poorly understood aspects of the genetic background of the affected individual. Adoption of this alternative view of the origin of RA will have significant consequences for future research and for development of new therapeutic interventions for this burdensome condition.

Keywords: rheumatoid arthritis pathogenesis etiologic studies genetic background.

Figure 1

Linkage diagram showing potential genetic associations with several autoimmune diseases. Copyright © 2007, National Academy of Sciences U.S.A. Adapted with permission from Goh KI, Cusick ME, Valle D, Childs B, Vidal M, Barabasi AL. The human disease network. Proc Natl Acad Sci U S A. 2007;104:8685–8690. Abbreviations: MS, multiple sclerosis; BLS, bare lymphocyte syndrome; AML, acute myelogenous leukemia; GVHD, graft vs host disease; HIV, human immunodeficiency virus; PDD, platelet defect deficiency; IDDM, insulin-dependent diabetes mellitus; RA, rheumatoid arthritis; SLE, systemic lupus erythematosus; RUNX1, runt-related transcription factor 1; CIITA, Class II, major histocompatibility complex, transactivator; IL-10, interleukin 10, PTPN22, protein tyrosine phosphatase nonreceptor 22.