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Rheumatoid factor, HLA-DR4, and allelic variants of DRB1 in women with recent-onset rheumatoid arthritis.

OBJECTIVE
To examine the relationship of rheumatoid factor (RF) to HLA-DR4 and alleles of DRB1 in women with recent-onset rheumatoid arthritis (RA).


METHODS
Incident cases of RA were identified as part of a prospective, population-based case-control study. HLA typing was completed for 246 cases meeting criteria for definite or classic RA.


RESULTS
One hundred thirty-six patients (55%) were positive for DR4, and 130 (53%) were RF positive. DR4 was found to be strongly associated with seropositivity (odds ratio 4.1, P < 0.0001). Patients with a shorter interval from RA onset to RF testing had a higher frequency of seropositivity than those with a longer interval (< or = 18 months 60%, > 18 months 33%). Further analysis of patients who had RF testing within 18 months of RA onset showed that the frequency of seropositivity was significantly greater among DR4-positive patients who had the shared sequence stretch of DR beta 1 associated with RA susceptibility (76% RF positive) than among DR1-positive patients who had this sequence (45% RF positive) (odds ratio 3.8, P = 0.01). Moreover, the frequency of seropositivity among DR1-positive patients with the sequence did not differ from that among all patients without the shared sequence (47%) (odds ratio 0.9, P = 0.8).


CONCLUSION
HLA-DR4 is strongly associated with seropositivity in women with recent-onset RA. The amino acid sequence of DR beta 1 that is associated with susceptibility to RA and is shared between DR4 and DR1 appears not to be the primary determinant of seropositivity in these women.