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Normal serum indices of bone collagen biosynthesis and degradation in small for gestational age infants
R Namgung1, R C Tsang, R I Sierra
1Department of Pediatrics, Yonsei University College of Medicine, Seoul, Korea.
Insights
Newborns small for gestational age (SGA) do not show altered bone collagen metabolism. Serum markers for bone collagen type I (PICP and ICTP) were similar in SGA and appropriate for gestational age (AGA) infants, suggesting mineral supply, not collagen defects, affects bone mineral content.
Area of Science:
- Pediatric Endocrinology
- Neonatology
- Skeletal Biology
Background:
- Small for gestational age (SGA) infants exhibit lower bone mineral content (BMC) and osteocalcin.
- Low insulin-like growth factor-I (IGF-I) in SGA infants suggests altered collagen metabolism.
- Serum PICP and ICTP as markers for bone collagen type I biosynthesis and degradation have not been studied in SGA infants.
Purpose of the Study:
- To investigate serum carboxyterminal propeptide of type I procollagen (PICP) and cross-linked carboxyterminal telopeptide of type I collagen (ICTP) in term SGA infants.
- To determine if altered bone collagen type I biosynthesis or degradation contributes to reduced BMC in SGA infants.
Main Methods:
- Studied 19 term SGA and 38 term appropriate for gestational age (AGA) infants, matched for gestation and birth month.
- Measured serum concentrations of PICP and ICTP.
- Analyzed correlations between ICTP, osteocalcin, and PICP.
Main Results:
- No significant differences were found in serum PICP or ICTP concentrations between SGA and AGA infants.
- Serum ICTP correlated with osteocalcin and PICP in SGA infants, but not in AGA infants.
- Biochemical indices of bone collagen type I metabolism were similar in both groups.
Conclusions:
- Findings do not support altered fetal bone collagen type I biosynthesis or degradation in SGA infants.
- Reduced BMC in SGA infants is likely due to a lower supply of minerals, not defective collagen metabolism.
- Serum PICP and ICTP are not indicative of altered bone collagen turnover in term SGA infants.
Abstract:
Serum carboxyterminal propeptide of type I procollagen (PICP) and cross-linked carboxyterminal telopeptide of type I collagen (ICTP), new markers of bone collagen type I biosynthesis and degradation, have not been studied in small for gestational age (SGA) infants. In an earlier study, we found a lower bone mineral content (BMC) and decreased serum osteocalcin in SGA than in appropriate for gestational age (AGA) infants, supporting the thesis that decreased fetal bone formation is a cause of lower BMC in SGA. In view of the role of insulin-like growth factor-I (IGF-I) in the regulation of collagen type I synthesis and degradation, and low serum IGF-I concentrations in SGA infants, we hypothesized that serum PICP would be lower and serum ICTP would be higher in SGA than in AGA infants, reflecting decreased bone collagen type I biosynthesis or enhancement of bone collagen type I degradation in SGA. We studied 19 term SGA and 38 term AGA infants that were matched specifically 1:2 by gestation and birth month. There were no differences between SGA and AGA infants in serum PICP nor ICTP concentrations. Serum ICTP was correlated with osteocalcin and with PICP in SGA infants but not in AGA infants. Thus, serum biochemical indices of bone collagen type I biosynthesis and degradation in term SGA infants are similar to those in term AGA infants. These findings are not consistent with the thesis of altered fetal bone collagen type I biosynthesis or degradation in SGA. We suggest that the reduced bone mineral content in SGA infants is predominantly related to a lower supply of minerals rather than defective regulation of bone collagen type I metabolism.