Type I and type III procollagen propeptides in amniotic fluid of normal pregnancies and in a case of mild osteogenesis imperfecta

BACKGROUND: The propeptides derived from type I and III procollagens, PICP, PINP and PIIINP, indicate the synthesis of the corresponding collagens. Their circulating concentrations reflect the growth velocity in infants and children METHODS: We measured these propeptides in 145 samples of amniotic fluid of normal pregnancy. In addition, we have analysed an amniotic fluid and serum sample from a mother with osteogenesis imperfecta, and later the infant's serum sample was also collected for procollagen propeptide analysis. RESULTS: High concentrations of propeptides, 100-1000 times higher than those in adult serum, were found in early second trimester, decreasing significantly towards term, reflecting the decreased foetal growth rate. Interestingly, the amino-terminal propeptide of type I procollagen, PINP, decreased more that the corresponding carboxy-terminal propeptide, PICP, although both are in principle derived from the same protein. At both stages of pregnancy, the discrepant ratio of PICP to PINP indicated a molar excess of PINP. Abnormally low concentrations of PICP and PINP with normal PIIINP concentrations measured in amniotic fluid and in the serum indicated decreased synthesis of type I procollagen in a foetus/infant with mild osteogenesis imperfecta. CONCLUSIONS: Our data show a decrease in collagen synthesis with the stage of pregnancy and lower values of type I procollagen propeptides in a case of OI.