ELEVATED COLLAGEN TURNOVER IN NIGERIAN CHILDREN WITH CALCIUM-DEFICIENCY RICKETS

Calcium deficiency is a major etiological determinant of rickets in Ni gerian children and is accompanied by undermineralization of the devel oping bone matrix which is composed largely of type I collagen. We hav e assessed types I and III collagen metabolism by measuring the circul ating concentrations of the N- and C-terminal propeptides (intact PINP and PICP) and the C-terminal telopeptide (ICTP) of type I collagen, a nd the N-terminal propeptide (PIIINP) of type III collagen in 94 healt hy Nigerian children and in 44 children aged 1-5 years with active cal cium-deficiency rickets. In active rickets the mean levels of the four collagen metabolites were approximately twofold higher than in the he althy children, despite a wide variation of individual values. Mean in tact PINP was 812 +/- 279 versus 403 +/- 189 mu g/liter; PICP was 573 +/- 265 versus 348 +/- 229 mu g/liter; PIIINP was 16.8 +/- 8.6 versus 10.8 +/- 3.6 mu g/ liter, and ICTP was 28.4 +/- 17.2 versus 11.9 +/- 4 .1 mu g/liter (all P < 0.001), in rachitic and healthy children, respe ctively. Healthy children younger than 3 years had higher levels of al l the collagen metabolites than those between 3 and 5 years (all P < 0 .05). Alkaline phosphatase was greater in rickets than in the healthy group (P < 0.001) whereas mean osteocalcin levels were slightly lower (P = 0.09). 1,25(OH)(2)D correlated with all the collagen propeptides, but not with ICTP in the healthy children. No such correlations were found in rickets, where there was a poor inverse correlation between 1 ,25(OH)(2)D and ICTP. These data suggest that collagen turnover is ele vated in cases of calcium-deficiency rickets, where vitamin D status i s adequate, possibly indicating increased turnover of undermineralized osteoid.