Role of Wnt-signaling inhibitors DKK-1 and sclerostin in bone fragility associated with Turner syndrome

Purpose: Girls affected with Turner syndrome (TS) present with low bone mineral density (BMD) and osteopenia/osteoporosis. Thus, they have an increased risk to develop fractures compared to normal population. The aim of this study was to deepen the pathophysiology of skeletal fragility in TS subjects by evaluating the serum levels of Dickkopf-1 (DKK-1) and sclerostin, main regulators of bone mass, as well as the percentage of circulating osteoblast precursors (OCPs). Methods: Thirty-four TS girls and 24 controls were recruited. All subjects underwent anthropometric measures (height, weight, body mass index-BMI). A peripheral venous blood sample was collected to determine serum levels of active intact parathyroid hormone (PTH), 25-OH vitamin D, calcium, phosphorus, bone alkaline phosphatase (bALP), osteocalcin, sclerostin, DKK-1, RANKL and OPG. OCPs were detected by flow cytometry. In TS subjects bone mineralization was measured at lumbar spine by dual energy X-ray absorptiometry (DXA). Results: bALP, 25-OH Vitamin D, and osteocalcin levels were significant lower in TS subjects than in the controls. Statistically significant higher levels of sclerostin, DKK-1 and RANKL were measured in patients compared with the controls. The percentage of OCPs did not show significant differences between patients and controls. Sclerostin and DKK-1 levels were related with anthropometric parameters, bone metabolism markers, HRT, rhGH therapy, RANKL and lumbar BMAD-Z-score. Conclusion: TS patients showed higher levels of sclerostin and DKK-1 than controls which can be related to HRT, and to reduced bone formation markers as well as the increased bone resorption activity.