Osteogenesis imperfecta (OI) is caused by mutations in collagen type I genes. In contrast to OI type II, III and IV where there are the structural mutations, in OI type I decreased production of normal collagen is due to the presence of a null allele. Because both pharmacological and gene therapy approaches depend on type of mutation and its consequences, quick and proper diagnosis is required.
Aim of the study: Application of COL1A1 null allele detection and analysis of collagen synthesized by skin fibroblasts in OI type I diagnosis.
Material and methods: Analysis was carried out in 17 patients and 20 healthy persons. Collagen was labeled with [3H]proline in skin fibroblasts and analyzed with electrophoretic method (SDS-PAGE) and by digestion with collagenase from Clostridium histolyticum. Nucleic acids were isolated from fibroblasts or peripheral blood and null allele was identified using a COL1A1 gene polymorphism.
Results: In the group of 17 OI patients 11 were heterozygous for insertion of 4 bp in 3'UTR region of COL1A1. "Null allele" was identified in 7 patients with decreased collagen synthesis by about 50% and in 2 patients with decreased collagen synthesis by 80% and 15%. However, in one patient with decreased collagen synthesis by about 50%, both allele transcripts were present.
Conclusions: Application of 4 bp insertion in 3'UTR of COL1A1 gene to detect "null allele" confirmed clinical diagnosis in 9 among 17 OI patients. In 3 patients results of quantitative study of collagen and "null allele" detection were different, what indicate that for final diagnosis comprehensively studies are needed.