The Association of Serum Sclerostin Levels,Echocardiographic Parameters, Arteriovenous Fistula Thrombosis and Carpal Tunnel Syndrome in Maintenance Hemodialysis Patients

Sclerostin, the product of the SOST gene, located on chromosome 17, locus q11.2 in humans, was originally believed to be a non-classical Bone morphogenetic protein (BMP) antagonist.More recently Sclerostin has been identified as binding to LRP5/6 receptors and inhibiting the Wnt signalling pathway .Wnt activation under these circumstances is antagonistic to bone formation. Although the underlying mechanisms are unclear, it is believed that the antagonism of BMP-induced bone formation by sclerostin is mediated by Wnt signalling, but not BMP signalling pathways.

Sclerostin is produced by the osteocyte and has catabolic effects on bone formation. This protein, with a length of 113 residues, has a dssp secondary structure that is 28% beta sheet (6 strands; 32 residues. Sclerostin has an inhibitory effect on the lifetime of the osteoblast. Sclerostin production by osteocytes is inhibited by parathyroid hormone, mechanical loading and cytokines including oncostatin M, cardiotrophin-1 and leukemia inhibitory factor. Sclerostin production is increased by calcitonin. Thus, osteoblast activity is self regulated by a negative feedback system.Sclerostin was recently identified as a component of parathyroid hormone (PTH) signal transduction.

Chronic kidney disease (CKD) is associated with abnormalities in bone and mineral metabolism.Renal osteodystrophy (ROD) is one of the three components of chronic kidney disease-mineral and bone disorder (CKD-MBD. Patients with CKD may develop various types of bone disease, spanning the spectrum of extreme situations such as severe osteitis fibrosa, osteomalacia, mixed osteopathy, and adynamic bone disease. In addition, patients may have osteoporosis, which increases the risk for fractures, both in advanced and in less severe CKD stages (2- 4),which, in turn, result in excess mortality New advances in the pathogenesis of renal osteodystrophy (ROD) change the perspective from which many of its features and treatment are viewed. Calcium, phosphate, parathyroid hormone (PTH), and vitamin D have been shown to be important determinants of survival associated with kidney diseases. Now ROD dependent and independent of these factors is linked to survival more than just skeletal frailty.Furthermore, ROD is shown to be an underappreciated factor in the level of the serum phosphorus in CKD. The discovery and the elucidation of the mechanism of hyperphosphatemia as a cardiovascular risk in CKD change the view of ROD. Emerging current data suggests a promising role for serum measurements of sclerostin in addition to iPTH in the diagnosis of high bone turnover in chronic kidney disease-5D patients (dialysis patients).

The demonstration that the level of serum sclerostin,which is directly produced by osteocytes, is a good predictor for bone formation in patients with CKD may be of clinical interest.Because of the close relationship between ROD and cardiovascular disease, the aim of this study is to investigate the association between sclerostin, arteriovenous fistula thrombosis, echocardiography and carpal tunnel syndrome in maintenance hemodialysis patients.