To evaluate the influence of homozygosity for HLA-B27 on the radiographic damage in ankylosing spondylitis (AS).

A total of 368 AS patients with positive HLA-B27 status from the Observation Study of Korean spondyloArthropathy Registry (OSKAR) cohort were recruited for this study. HLA-B27 positive patients out of all AS patients were assessed for whether they had homozygosity or heterozygosity for HLA-B27. First, all data were stratified in relation to the carrier state of positive HLA-B27 for cross-sectional survey. Then we compared the radiographic damage score between groups. Second, we evaluated collected clinical and radiographic parameters at two different time points. Then we compared radiographic progression between groups. To use the mSASSS, cervical and lumbar spinal radiographs were examined by two experienced bone and joint radiologists (S. Lee, K.B. Joo).

The agreement between the two readers regarding mSASSS was very good: ICC coefficient 0.70 (95% CI 0.60–0.81). The mean age (SD) of the AS patients was 37.0 (9.2) years, and the mean disease duration (SD) was 15.6 (9.1) years. Of these patients, 34.5% (127 patients) had HLA-B27 homozygosity. The mean mSASSS unit (SEM) was not significantly different between groups (homozygosity 28.57±4.12 vs heterozygosity 23.34±3.44, P=0.344) on cross-sectional survey. When it comes to radiographic progression between groups over 5years, there was no significant difference in spite of adjusting for confounding variable (homozygosity 4.98±0.98 vs heterozygosity 4.21±0.82, P=0.562).

The carrier state of positive HLA-B27 plays no role in determining the radiographic progression in AS.