PLASMA OSTEOCALCIN IN HEALTHY NIGERIAN CHILDREN AND IN CHILDREN WITH CALCIUM-DEFICIENCY RICKETS

Osteocalcin is an osteoblast-specific protein believed to be associate d with events occurring during bone mineralization, which has been wid ely used clinically as an indicator of osteoblast function. Plasma ost eocalcin concentrations (pOC) were studied in 94 (59 male, 35 female) healthy and 44 (21 male, 23 female) rachitic Nigerian children, all on e to five years of age. The study was aimed at establishing a referenc e range for healthy Nigerian children determining any changes in plasm a osteocalcin levels occurring in children with calcium-deficiency ric kets. In the controls, pOC levels ranged from 3-89 ng/ml, with a mean value of 23 +/- 19 ng/ml. The values were higher in girls (29 +/- 21 n g/ml) than in boys (21 +/- 18 ng/ml), though not significantly. The co ntrols had values consistent with other published pediatric ranges fro m Europe and North America. In the younger rachitic children (under 3 years) the mean pOC was lower than in the controls (P = 0.04) despite the much elevated plasma levels of 1,25(OH)(2)D. In the controls, pOC correlated with 1,25(OH)(2)D (r = 0.59, P = 0.003), alkaline phosphata se (r = 0.22, P = 0.03), and inorganic phosphate (r = 0.27, P = 0.01). These correlations were lost in the rickets group. The findings in th e controls confirm the known association between plasma 1,25(OH)(2)D a nd circulating osteocalcin levels, whereas the findings in the rickets group suggest that the stimulatory effects of 1,25(OH)(2)D on osteoca lcin may depend on other permissive factors, such as normal circulatin g levels of calcium and phosphate.