[Molecular diagnosis of osteogenesis imperfecta type I]

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.

Application of COL1A1 null allele detection and analysis of collagen synthesized by skin fibroblasts in OI type I diagnosis.

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.

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.

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.