Differences in Bone Metabolism between Children with Prader–Willi Syndrome during Growth Hormone Treatment and Healthy Subjects: A Pilot Study

Despite therapy with growth hormone (GH) in children with Prader-Willi syndrome (PWS), low bone mineral density and various orthopedic deformities have been observed often. Therefore, this study aimed to analyze bone markers, with an emphasis on vitamin K-dependent proteins (VKDPs), in normal-weight children with PWS undergoing GH therapy and a low-energy dietary intervention. Twenty-four children with PWS and 30 healthy children of the same age were included. Serum concentrations of bone alkaline phosphatase (BALP), osteocalcin (OC), carboxylated-OC (Gla-OC), undercarboxylated-OC (Glu-OC), periostin, osteopontin, osteoprotegerin (OPG), sclerostin, C-terminal telopeptide of type I collagen (CTX-I), and insulin-like growth factor-I (IGF-I) were determined using immunoenzymatic methods. OC levels and the OC/CTX-I ratios were lower in children with PWS than in healthy children (<i>p</i> = 0.011, <i>p</i> = 0.006, respectively). Glu-OC concentrations were lower (<i>p</i> = 0.002), but Gla-OC and periostin concentrations were higher in patients with PWS compared with the controls (<i>p</i> = 0.005, <i>p</i> < 0.001, respectively). The relationships between IGF-I and OC (<i>p</i> = 0.013), Gla-OC (<i>p</i> = 0.042), and the OC/CTX-I ratio (<i>p</i> = 0.017) were significant after adjusting for age in children with PWS. Bone turnover disorders in children with PWS may result from impaired bone formation due to the lower concentrations of OC and the OC/CTX-I ratio. The altered profile of OC forms with elevated periostin concentrations may indicate more intensive carboxylation processes of VKDPs in these patients. The detailed relationships between the GH/IGF-I axis and bone metabolism markers, particularly VKDPs, in children with PWS requires further research.