Bone turnover in children with vitamin D deficiency rickets before and during treatment

Abstract

Biochemical markers of bone formation [alkaline phosphatase, osteocalcin, and carboxyterminal propeptide of type I procollagen (PICP)] and bone resorption [cross-linked carboxyterminal telopeptide of type I collagen (ICTP) and cross-linked N-telopeptides of type I collagen (NTX)] were measured in 14 children aged 8.5-10.5 mo with vitamin D deficiency rickets before and longitudinally during vitamin D treatment (3000-4000 IU/daily). Forty-four healthy children aged 8-10.5 mo were enrolled as sex- and age-matched controls. Before treatment, serum levels of alkaline phosphatase, PICP, and ICTP, and urinary excretion values of NTX were significantly higher, and serum osteocalcin levels significantly lower than controls (31.4 +/- 3.5 microkat/L and 9.8 +/- 2.9 microkat/L, p < 0.001; 1025 +/- 89 microg/L and 952 +/- 97.4 microg/L, p < 0.02; 15.6 +/- 2.6 microg/L and 14.2 +/- 1.3 microg/L, p < 0.01; 370.7 +/- 109.4 nmol BCE and 201.8 +/- 69.2 nmol BCE, p < 0.001: 17.6 +/- 9.1 microg/L and 22.5 +/- 7.6 microg/L, p < 0.05, respectively). During treatment, serum alkaline phosphatase levels progressively declined in association with the radiographic healing of the skeletal lesions. Serum levels of osteocalcin, PICP, and ICTP, and urinary excretion values of NTX showed a transient but significant (p < 0.05 to p < 0.001) increase in comparison with baseline values during the first 2-4 wk of treatment, and decreased slowly thereafter. They were within the mean +/- 2 SD of controls before the recovery of the skeletal lesions.

Conclusions: These findings suggest that children with vitamin D deficiency rickets have increased bone turnover before and during the first weeks of treatment. Alkaline phosphatase is a more reliable marker than osteocalcin, PICP, ICTP and NTX for diagnosing and monitoring these patients.