Objective: To assess the extent of ethnic variation in the clinical expression of rheumatoid arthritis (RA) and the role of HLA-DRB1 alleles in this variation.
Methods: We assessed consecutive RA patients for joint findings, subcutaneous nodules, laboratory and radiographic findings, and treatment. We typed HLA-DRB1 alleles to identify those that contain the shared epitope (SE). We adjusted ethnic comparisons for age and sex, and tested for ethnic heterogeneity in the effect of the SE.
Results: We studied 777 RA patients, 498 of whom were women (64%), 432 were Hispanic (56%), 272 were non-Hispanic white (NHW; 35%), 53 were African American (AA; 7%), and 20 were Asian (3%). Compared with NHW, Hispanics had significantly more tender joints (17 versus 11), more swollen joints (8 versus 7), more frequent rheumatoid factor (RF) positivity (93% versus 84%), higher erythrocyte sedimentation rate (ESR; 45 versus 36 mm/hr), and a lower number of lifetime disease-modifying antirheumatic drugs (1.9 versus 2.5). AA were older at onset (46 versus 44 years), had less frequent subcutaneous nodules (18% versus 28%), and higher ESR (42 versus 36 mm/hour) than did NHW. Hispanics and AA were more likely than NHW to be null for the SE (odds ratio [OR] = 4.59 for AA; and OR = 1.61 for Hispanics), and less likely to have 2 SE-carrying alleles (OR = 0.59 for Hispanics and OR = 0.25 for AA). The number of SE copies was associated with subcutaneous nodules, ESR, RF, and radiographic changes. Ethnic heterogeneity in the effect of the SE was modest.
Conclusions: There is ethnic variation in the clinical expression of RA and in both the frequency and types of SE-carrying HLA-DRB1 alleles. Some ethnic variation in clinical findings is associated with differences in SE frequency. However, we found that the effect of the SE on the clinical features of RA varies little between ethnic groups.