ESPE Abstracts

Introduction: Prader-Willi syndrome (PWS) is a rare congenital neurodevelopmental disorder characterized by hyperphagia, growth hormone (GH) deficiency, short stature, and low bone mineral density. The mechanisms concerning bone metabolism disturbances in these patients are still unclear. An important role in the process of bone formation is played by osteocalcin (OC), the most abundant non-collagen protein of the bone matrix. OC has three potential gamma-carboxyglutamic acid residues that are responsible for the binding of OC to hydroxyapatite. In the circulation, carboxylated (Gla-OC) and undercarboxylated (Glu-OC) forms of OC are present. The aim of this study was to analyze both forms of osteocalcin in non-obese children with PWS in comparison with normal-weight controls.

Patients and Methods: The study consisted of eighteen children (aged 1-12 years) with PWS during treatment with growth hormone (GH) and dietary intervention. The control group consisted of eighteen healthy, normal-weight children (BMI z-score <-1+1>). We determined the levels of OC, Gla-OC, Glu-OC, insulin-like growth factor-I (IGF-I) and IGF-binding protein 3 (IGFBP3) by ELISA kits. Anthropometric measurement (body weight, height, body mass index - BMI) and dietary intake (energy and macronutrients intake) were assessed in all studied children. This study was approved by the Ethics Committee at the Institute of Mother and Child.

Results: The daily energy intake in children with PWS was lower by about 30% (P<0.001) compared with the controls. Daily dietary protein intake was similar in both studied groups, but carbohydrate and fat intakes were significantly lower in the patient group than in the controls (P<0.001). Similar values of BMI were observed in both studied groups of children. The concentration of OC was significantly lower in patients in comparison with the controls (P=0.02). The values of Gla-OC were higher (P=0.008), but the values of Glu-OC were lower (P=0.001) in patients with PWS than healthy children. Positive correlation was found between Gla-OC and IGF-I/t-IGFBP3 ratio (r= 0.433; P<0.05) in patient group.

Conclusions: An altered profile of OC forms was found in non-obese children with Prader-Willi syndrome during treatment with GH and reduced energy intake. These changes may be related to disorders of bone metabolism in patients with PWS.