A study of human collagen genes and the molecular genetics of osteogenesis imperfecta.

The human collagens are a family of related proteins which all possess at least one triple helical domain characterised by a Gly-Xaa-Yaa amino acid repeat motif where Xaa and Yaa are frequently proline and hydroxyproline respectively. This repetitive structure is determined by the characteristic sequence of the genes encoding the component polypeptides. Mutations in the COL1A1 and COL1A2 genes, encoding the proalpha1(I) and proalpha2(I) chains of type I collagen have been reported. These mutations can alter the polypeptide chains of type I collagen and interfere with the nature or amount of mature collagen produced by the cell and have been implicated as the cause of the connective tissue disorder osteogenesis imperfecta (brittle bone disease). This disorder is heterogeneous in nature with phenotypes ranging from mild to lethal in the perinatal period. In this study, single strand conformation polymorphism analysis was coupled with DNA sequencing in order to identify mutations in type I collagen genes which could be responsible for the disorder phenotype in a number of patients. Three novel glycine by serine substitutions were identified, two of which were found to be shared by more than one unrelated individual - a phenomenon rarely observed for osteogenesis imperfecta mutations. The fourth mutation was the first glycine by glutamic acid substitution reported to be the cause of this disorder. All of these substitutions occurred within the triple helical region of the proalpha2(I) chain. These data add to the knowledge of the relationship between the position and nature of substituting amino acids and the resulting phenotypes. In addition, two novel but neutral sequence variants were identified. A novel source of collagen mRNAs based upon basal transcription levels was also investigated as was an approach for identifying novel collagenous sequences using degenerate oligonucleotide-primed polymerase chain reaction amplification of DNA.