HLA DM is a non-classical major histocompatibility complex (MHC) class II molecule that has been shown to facilitate peptide loading with classical class II molecules.
In this study, we analysed the polymorphism in exon 3 of HLA DMA and DMB genes by a polymerase chain reaction-sequence-specific oligonucleotide probe method in 163 rheumatoid arthritis (RA) patients and 146 ethnically matched controls. The HLA-DRB1 genotype was also analysed by a reverse-dot blot method.
Our results show in RA patients a significant increase in the HLA DMB*0101 allele frequency (83% vs 72.3% of the controls, P < 1.6 x 10(-3), significance at P < 0.0125) and in the HLA DMB*0101-0101 homozygote genotype frequency [70.8% vs 50% of the controls, P < 4.2 x 10(-4), significance at P < 0.00625, odds ratio (OR) = 2.4, 95% confidence interval (CI): 1.43-4]. The increase in DMB*0101 allele and homozygote genotype frequencies was independent of a linkage disequilibrium between DMB and DRB1 alleles. The analysis of non-random associations between the HLA-DM and DRB1 alleles only revealed a significant association in controls between DMB*0104 and DRB1*07 alleles (delta = 0.01, P < 7 x 10(-4), significance at P < 9.6 x 10(-4)). On the other hand, the DMB*0101-0102 genotype frequency was increased in DRB1*0401-negative RA patients as compared to controls (11% vs 2%, P < 0.011, significance at P < 0.015, OR = 6.2, 95% CI: 1.2-30).
Our data suggest that HLA-DM alleles could play a role in the genetic susceptibility to RA.