HLA Allele Prevalence in Disease-Modifying Antirheumatic Drugs-Responsive Enthesitis and/or Arthritis Not Fulfilling ASAS Criteria: Comparison with Psoriatic and Undifferentiated Spondyloarthritis

Spondyloarthritis (SpA) is a group of inflammatory rheumatic diseases characterized by common clinical features, such as inflammatory enthesitis, arthritis and/or back pain. SpA is strongly associated with human leukocyte antigen (HLA) class I allotype B27. Ankylosing spondylitis has historically been the SpA subgroup with one of the strongest, best-proven associations with HLA-B27. The remaining SpA subgroups, namely psoriatic arthritis (PsA), inflammatory bowel diseases-associated arthritis/spondylitis, reactive arthritis, and undifferentiated SpA (uSpA), have also been associated with HLA allotypes other than HLA-B27. In this retrospective study, we analyzed the association between the HLA class I and II haplotypes and the susceptibility to enthesitis and/or arthritis (E/A). Special attention was paid to E/A responding to disease-modifying antirheumatic drugs (DMARDs) not fulfilling ASAS classification criteria (ASAS(-)), as compared to ASAS(+) forms including PsA and uSpA. The whole E/A group showed significant independent associations with HLA-A28(68), B27, Cw3, Cw12, and DQ1; taken singly, PsA was associated with HLA-B27 and DQ1, uSpA with HLA-B16(38,39) and B27, and E/A ASAS(-) with HLA-A28(68), Cw8, and Cw12. This study identified novel risk HLA allotypes for different SpA subgroups in an Italian population. HLA typing could aid the diagnosis and treatment of E/A subgroups, including DMARDS-responsive forms not fulfilling ASAS classification criteria.

Automated summary

Spondyloarthritis (SpA) is a group of inflammatory rheumatic diseases strongly associated with HLA-B27, with different SpA subgroups showing varying associations with different HLA allotypes. This study in an Italian population identified novel risk HLA allotypes for different SpA subgroups, which could aid in diagnosis and treatment.