Among the studied bone formation markers, we observed significantly lower concentrations of OC (p < 0.001), but significantly higher concentrations of periostin (p < 0.001), and a tendency toward higher values of carboxylated-OC (Gla-OC) (p = 0.068) in children with PWS than in healthy subjects. The gene discussed is POSTN; the disease is Prader-Willi syndrome.