Bsm I polymorphism in the vitamin D receptor gene is related to bone collagen turnover in healthy infants.

We examined the vitamin D receptor genotypes (BB, Bb and bb) defined by the Bsml restriction endonuclease in relation to biochemical indices of bone metabolism in healthy Caucasian infants. We measured the serum concentrations of the carboxy-terminal propeptide of type I procollagen (PICP) and the urinary excretion of total pyridinoline, free, total and bound deoxypyridinoline, the type I collagen N-terminal and C-terminal cross-linked telopeptides. The concentrations of the urinary indices are expressed relative to creatinine. Subjects with BB genotype had the highest mean concentrations of free, total and bound deoxypyridinoline and of the N-terminal cross-linked telopeptide (PANOVA = 0.0016, 0.0004, 0.0002 and 0.0053, respectively). BB boys had a higher excretion of the C-terminal cross-linked telopeptide than the other genotypes (PANOVA = 0.0253). In a subgroup of homozygotes aged 10 (1) months, BB subjects had the highest levels of the C-terminal cross-linked telopeptide (p=0.03), and of total deoxypyridinoline (p=0.02) and pyridinoline (p=0.06) concentrations. No significant association between the vitamin D receptor genotype and PICP was found. These data suggest that there may be a contribution of the vitamin D receptor genotype to skeletal metabolism in early childhood.

Procollagen propeptide and pyridinium cross-links as markers of type I collagen turnover: sex- and age-related changes in healthy children.

The correlations among age, gender, body size parameters, and type I collagen metabolism were evaluated in 183 healthy infants, aged 8.5-27.5 months. Collagen formation was assessed by measuring serum type I collagen carboxy-terminal propeptide, and degradation was determined by urinary pyridinoline and deoxypyridinoline (measured by high performance liquid chromatography) and cross-linked N- and C-terminal telopeptides of type I collagen (measured by NTx and CrossLaps assays). A new RIA specific for deoxypyridinoline was also evaluated. The results provide reference values at 10 months and 2 yr of age, including cross-linked C-terminal telopeptides (1492 +/- 685 and 1510 +/- 446 in boys; 1705 +/- 612 and 1849 +/- 611 micrograms/mmol creatinine in girls; mean +/- 1 SD). There was a good correlation between the high performance liquid chromatography and RIA data for deoxypyridinoline, showing that the RIA method is suitable for use in healthy children. Some correlations were found among peptide-bound cross-links, serum type I collagen carboxy-terminal propeptide, and the anthropometric parameters, suggesting that these peptides reflect bone resorption and also overall body type I collagen. Finally, there were age- and sex-related differences in the urinary excretion of the collagen degradation markers, suggesting that, unlike boys, girls maintain a high degree of collagen degradation up to the age of 24 months despite a decrease in their rate of collagen formation.