Higher Level of Dickkopf-1 is Associated with Low Bone Mineral Density and Higher Prevalence of Vertebral Fractures in Patients with Ankylosing Spondylitis

Patients with ankylosing spondylitis (AS) have an increased risk of bone loss and vertebral fractures. In this study, we explored the hypothesis that the excess bone loss and vertebral fractures might be related with the activity of the Wingless signaling pathway, and in particular with the serum levels of its circulating inhibitors, Sclerostin and Dickkopf-1 (DKK1). We recruited 71 patients diagnosed with AS. Lateral radiographs of the total spine were analyzed to detect the presence of vertebral fractures, and bone mineral density (BMD) was assessed in all patients using dual X-ray absorptiometry at lumbar spine and proximal femoral site. Blood samples were obtained and levels of C-reactive protein (CRP), DKK1, and Sclerostin were measured. Blood samples from 71 healthy sex- and age-matched volunteers were collected to be used as controls. Vertebral fractures were detected more commonly among men than in women (29 vs 8 %, respectively). DKK1, but not Sclerostin serum levels, were inversely correlated to lumbar spine Z-score BMD. Patients with one or more prevalent vertebral fractures had significantly higher DKK1 levels, without significant difference in Sclerostin serum levels. A significant positive correlation was found between DKK1 serum levels and CRP (r = 0.240, p = 0.043). The association we found between serum DKK1 levels and BMD values and vertebral fracture prevalence suggests that DKK1 might contribute to the severity of osteoporosis in AS.