Objective: To evaluate HLA-DRB1 associations in polymyalgia rheumatica (PMR) and giant cell arteritis (GCA) compared to rheumatoid arthritis (RA).
Methods: One hundred twenty-one patients were included and oligotyped: 79 with PMR alone and 42 with GCA (14 also had PMR). We also genotyped 1609 healthy controls and 433 patients with RA. Statistical analysis included Fisher's exact test and calculation of the odds ratio (95% CI).
Results: Compared to controls, the DRB1*04 phenotype was increased in PMR (39.2%; OR = 2.4, p = 0.0005) and GCA (45.2%; OR = 3.1, p = 0.0005). This association was weaker than in RA (p = 0.01). DRB1*07 was more frequent in GCA (31.0%) than in PMR (13.4%; p = 0.03), but the difference was not significant in comparison to controls. The distribution of DRB1*04 subtypes was similar in PMR and GCA, but different from RA and controls. However, the frequency of 0402 and 0403 subtypes could not be distinguished from that in patients with RA. Double occurrence of RA associated alleles was less frequent in PMR and GCA (9.9%; p = 0.005) than in patients with RA (20.8%). There was no significant relationship between markers of disease activity/severity and HLA-DRB1 genes in PMR or GCA.
Conclusion: PMR and GCA were associated with HLA-DRB1*04, but more weakly than RA. Nevertheless, these data suggest that HLA-DRB1* genes are closely related to susceptibility in PMR, GCA, and RA and do not support the hypothesis of a different linkage to the 3rd hypervariable region of DRB1 alleles. By contrast with RA, HLA-DRB1* genes do not appear to be indicators of disease severity in PMR and GCA.