Clinical significance of possible HLA biomarkers in axial spondyloarthritis beyond HLA-B27 positivity

The aim of this study is to compare four forms of axial spondyloarthritis (axSpA): non-radiographic axial spondyloarthritis (nr-axSpA), ankylosing spondylitis (AS), non-radiographic axial psoriatic arthritis (nr-axPsA) and radiographic axial psoriatic arthritis (r-axPsA). In a cross-sectional retrospective study, gender difference, human leukocyte antigen (HLA) typing, laboratory C-reactive protein (CRP) and erythrocyte sedimentation (SE) values, and radiographic and magnetic resonance scans were analyzed. One hundred and thirty-seven patients were included in the study: 45 AS, 51 nr-axSpA, 32 r-axPsA and 9 nr-axPsA; 74 women and 63 men. Most of the gender, laboratory and radiological findings confirmed the results of previously conducted studies about each group of the investigated axSpA. The key findings of our study are the newly detected findings of HLA typing beyond HLA-27 positivity: HLA-DR16 in AS, HLA-DR11 in nr-axSpA, HLA-B13, HLA-B57, HLA-Cw12 and HLA-DR7 in r-axPsA, and HLA-B18 in nr-axPsA. Our study also confirmed some of the results of previously conducted studies on predominant genes of HLA typing in axSpA: HLA-B27 in AS, HLA-B39 and HLA-Cw6 in r-axPsA, and HLA-Cw7 in nr-axPsA. Important conclusions about the nr-axPsA group cannot be drawn because of the very small number of subjects included in this group of axSpA. Our results suggest that the newly detected HLA typing findings beyond HLA-B27 positivity could be possible biomarkers of early detection of axSpA, but further studies on larger samples are needed.