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Opposing effects of the D70 mutation and the shared epitope in HLA-DR4 on disease activity and certain disease phenotypes in rheumatoid arthritis

¹ Division of Pharmacoepidemiology, Brigham and Women’s Hospital, Harvard Medical School, Boston, Massachusetts, USA
² Division of Rheumatology, Brigham and Women’s Hospital, Harvard Medical School, Boston, Massachusetts, USA
³ Millennium Pharmaceuticals Inc., Cambridge, Massachusetts, USA
⁴ Cardiovascular Medicine, Duke University Medical Center, Durham, North Carolina, USA

Correspondence to:
Nancy A Shadick, MD, MPH, Division of Rheumatology, Immunology, Allergy, Brigham and Women’s Hospital, Harvard Medical School, Boston, Massachusetts 02115, USA; nshadick{at}partners.org

Background: Certain sequences present in the hypervariable region of human leucocyte antigen (HLA)-DRB1 known as the shared epitope (SE) are hypothesised to increase the risk of rheumatoid arthritis (RA), whereas alleles encoding aspartic acid at position 70 (D70 alleles) may have a protective effect.

Methods: Patient HLA-DRB1 serotypes were assessed and the genotypes encoding the SE motif or the putatively protective D70 motif identified in a large RA cohort. Logistic regression was used to analyse associations of genotype with presence of disease, comorbidities and disease severity, and association between genotype and change in disease activity over time.

Results: The 689 patients enrolled had a mean (SD) age of 57.9 (13.7) years and mean (SD) disease duration of 15.3 (12.7) years. In a comparison with 482 ethnicity matched population-based controls, the D70 sequence exerted a strong protective effect (OR = 0.52, p<0.001) that remained significant when the SE at the same locus was accounted for (OR = 0.72, 95% CI 0.60 to 0.86, p<0.001). The SE assessed on all HLA-DRB1 serotypic backgrounds except DR1 was associated with RA susceptibility (additive OR = 2.43, p<0.001). Associations were found between SE and serum levels of rheumatoid factor (p<0.001, with correlation of 0.18) and anti-cyclic citrullinated peptide antibodies (p<0.001, with correlation of 0.25) but not with serum C-reactive protein.

Conclusion: The D70 allele has a significant protective effect that is mitigated but still significant when the risk effect of the SE at the same locus is taken into account. The presence of the SE on DR4 is associated with greater RA susceptibility and certain disease-activity measures.

Abbreviations: ACR, American College of Rheumatology; AVHR, allelic hypervariable regions; BRASS, Brigham and Women’s Rheumatoid Arthritis Sequential Study; CCP, cyclic citrullinated peptide; CRP, C-reactive protein; DAS, Disease Activity Score; HLA, human leucocyte antigen; JRS, joint-replacement surgery; MDHAQ, Multidimensional Health Assessment Questionnaire; RA, rheumatoid arthritis; RF, rheumatoid factor; SE, shared epitope

Keywords: rheumatoid arthritis; genetics; shared epitope; patient registry