Bone morphogenetic proteins and Dickkopf-1 in ankylosing spondylitis

Objectives: To determine bone morphogenetic proteins (BMPs) and Dickkopf homologue-1 (Dkk-1) levels in ankylosing spondylitis (AS). Method: Serum BMPs and Dkk-1 were measured in 72 AS patients and 30 healthy controls. For AS patients, we recorded the demographic data, disease activity, functional index, and global assessment with questionnaires, and image changes with roentgenography. We also measured human leucocyte antigen-B27 and systemic inflammatory reactants. Results: BMPs were higher but Dkk-1 was significantly lower in AS patients than in controls. Dkk-1 was higher in AS patients who received non-steroidal anti-inflammatory drugs (NSAIDs) regularly in the past year (p = 0.001). Serum BMP-7 level and the BMP-7/Dkk-1 ratio correlated significantly with sacroiliitis severity, Bath Ankylosing Spondylitis Radiology Index (BASRI)-total, modified Stoke Ankylosing Spondylitis Spinal Score, and disease duration. There were also significant positive correlations among serum levels of BMP-2, -4, and -6, BASRI-total, and disease duration (p < 0.05). However, BMP-2/Dkk-1 was only significantly correlated with disease duration. The calculated area under the standard receiver operating characteristics curve suggested that BMP-2/Dkk-1 and serum BMP-2 are good indicators to predict disease activity, functional index, and patient global assessment in AS patients. Conclusion: BMPs and BMPs/Dkk-1 were significantly correlated with disease activity, and radiological and functional indices in AS patients. Dkk-1 was lower in AS patients than in controls. Among AS patients, Dkk-1 was higher in those taking NSAIDs regularly. BMP or Dkk-1 may be taken as a biomarker for disease severity or a treatment outcome predictor in AS, but this needs further study.