Low Frequency of HLA-B27 in Ankylosing Spondylitis Patients from Turkey: Insights from the Thrace Region

BACKGROUND This study aimed to evaluate the frequency of human leukocyte antigen (HLA)-B27 in 488 patients with ankylosing spondylitis (AS) from the Thrace region of Turkey and to assess its association with clinical and radiological features. MATERIAL AND METHODS A retrospective analysis was conducted on patients diagnosed with AS according to the modified New York criteria and/or Assessment of Spondyloarthritis International Society (ASAS) classification criteria. HLA-B27 status was determined using real-time polymerase chain reaction (PCR). Clinical data, including disease activity indices such as Bath AS disease activity index (BASDAI), Bath AS functional index (BASFI), C-reactive protein (CRP), erythrocyte sedimentation rate (ESR), and radiological findings were analyzed. Statistical comparisons were performed using chi-square, Mann-Whitney U, Spearman's correlation, and logistic regression models. RESULTS Among 488 AS patients, 59.43% were HLA-B27 positive. HLA-B27 positivity was significantly associated with male sex (p=0.020), earlier disease onset (p=0.021), higher CRP (p=0.020) and ESR (p=0.04) levels, and the initial BASDAI and initial BASFI scores (p=0.042 and p=0.044). A strong correlation was found between HLA-B27 positivity and sacroiliitis severity on X-ray (p=0.016, OR: 1.518) and magnetic resonance imaging (MRI) (p=0.001, OR: 1.199). No significant associations were observed between HLA-B27 status and extra-articular manifestations. CONCLUSIONS The HLA-B27 frequency in Thracian AS patients (59.43%) was lower than reported in Western populations but consistent with some Turkish studies. HLA-B27 positivity was associated with earlier disease onset, male predominance, and more severe sacroiliitis. These findings highlight regional variations in AS presentation and the role of HLA-B27 in disease severity.