Allelic markers close to prolactin are associated with HLA-DRB1 susceptibility alleles among women with rheumatoid arthritis and systemic lupus erythematosus

Objective. To investigate linkage disequilibrium between HLA-DRB1 disease susceptibility alleles and microsatellite markers close to the prolactin gene, among women with rheumatoid arthritis (RA) and systemic lupus erythematosus (SLE) and normal controls. Methods. DNA from 89 women with RA, 76 women with SLE, and 94 controls was typed for HLA-DRB1 status and D6S422 and D6S285, 2 highly polymorphic microsatellite markers close to the prolactin gene. RA patients were stratified by DRB1*0401 status, and SLE patients were stratified by *0301 status. Results. There was an excess frequency of D6S422*1 among SLE patients with DRB1*0301 (odds ratio [OR] 3.1). The frequency of this allele was also slightly in excess among RA patients with DRB1*0401 (OR 1.9). D6S285*5 was also in excess among female RA patients with DRB1*0401 (OR 3.5), and was slightly increased among female SLE patients with DRB1*0301. None of these alleles were found to be increased among *0401-positive or *0301-positive controls. Conclusion. These data indicate that there may be linkage disequilibrium between HLA-DRB1 alleles and microsatellite marker alleles close to the prolactin gene among women with RA and SLE. This suggests the possibility of extended haplotypes encoding for HLA-DRB1 susceptibility and high prolactin production, which contribute to susceptibility to both RA and SLE.