The molecular genetics of human collagen genes and osteogenesis imperfecta.

The collagens are the most abundant proteins in the human body. Their function is predominantly structural. The mature collagen protein is composed of three polypeptides which form triple helical structures. The genes coding for the collagens are large, complex and semi-dispersed throughout me human genome. They are expressed in a tissue specific, developmentally regulated manner. Analysis of the fibrillar collagen protein and gene sequences has revealed a high degree of conservation. A possible variant in the cDNA sequence coding for 1(III) was investigated. The variant sequence was phenotypically silent and coded for an amino acid in the carboxyl end of the helical domain. The variant base was shown to be an artefact introduced during cDNA synthesis. Many mutations causing the disease osteogenesis imperfecta (OI) have been described in the literature. Most are point mutations causing single amino acid substitutions. The mutation causing a Sillence type III OI phenotype was determined. It was found to be an inframe 3bp deletion which resulted in the loss of the last amino acid coded for by exon 19 of COL1A2, a valine. The mutation, like many of those in the type I collagen genes which cause OI, coincided in its position with the start of overmodification of the patients type I collagen molecules. 15 collagen types have been at least partially characterized to date. In an attempt to characterize new collagen cDNA sequences a library was produced which was intended to be enriched with collagen coding sequences. The production of such a library relied on the ability of a polymerase chain reaction primer to selectively amplify cDNA sequences coding for the helical domains of collagens. The library contained collagen sequences, but not enough to make screening the library for new collagen sequences by random sequencing of clones a viable proposition. This work continues.