Sclerostin and Dkk-1 in Patients with Ankylosing Spondylitis

Objective: To determine the serum Dickkopf-related protein 1 (Dkk-1) and sclerostin levels, and their relationship to structural damage and disease activity in patients with ankylosing spondylitis (AS), as well as to compare the serum Dkk-1 and sclerostin levels in the patients receiving and not receiving anti-TNF-α treatment. 
Materials and Methods: This cross-sectional study included 44 AS patients with AS and 41 healthy age- and -gender-matched controls. Demographic datas, disease activity parameters, and Bath Ankylosing Spondylitis Radiologic Index (BASRI) scores were recorded. Serum Dkk-1 and sclerostin levels were measured using a commercially available ELISA. 
Results: Serum Dkk-1 levels were lower (P > 0.05) and sclerostin levels were significantly lower (P < 0.05) in the AS patients than in the controls. Dkk-1 and sclerostin levels were similar in the patients that did and didn’t receive anti-TNF-α treatment, and in the patients with active and inactive disease (P > 0.05). There wasn’t a correlation between serum Dkk-1 or sclerostin levels, and disease activity indices (P > 0.05). BASRI scores did not correlate with serum Dkk-1 levels or sclerostin levels (P > 0.05). 
Discussion: Sclerostin expression is impaired in AS, but this is not the case for Dkk-1. The lack of an association between Dkk-1 or sclerostin levels, and anti-TNF-α treatment, disease activity indices, and radiological damage might indicate that neither the Dkk-1 nor sclerostin level induce inflammation and radiological damage in AS patients. Pathologic bone formation in AS may be due to molecular dysfunction of sclerostin and Dkk-1 at the cellular level.