ANALYSIS OF THE COL1A1 AND COL1A2 GENES BY PCR AMPLIFICATION AND SCANNING BY CONFORMATION-SENSITIVE GEL-ELECTROPHORESIS IDENTIFIES ONLY COL1A1 MUTATIONS IN 15 PATIENTS WITH OSTEOGENESIS IMPERFECTA TYPE-I - IDENTIFICATION OF COMMON SEQUENCES OF NULL-ALLELE MUTATIONS

Although >90% of patients with osteogenesis imperfecta (OI) have been estimated to have mutations in the COL1A1 and COL1A2 genes for type I procollagen, mutations have been difficult to detect in all patients w ith the mildest forms of the disease (i.e., type I), In this study, we first searched for mutations in type I procollagen by analyses of pro tein and mRNA in fibroblasts from 10 patients with mild OI; no evidenc e of a mutation was found in 2 of the patients by the protein analyses , and no evidence of a mutation was found in 5 of the patients by the RNA analyses, We then searched for mutations in the original 10 patien ts and in 5 additional patients with mild OI, by analysis of genomic D NA, To assay the genomic DNA, we established a consensus sequence for the first 12 kb of the COL1A1 gene and for 30 kb of new sequences of t he 38-kb COL1A2, gene, The sequences were then used to develop primers for PCR for the 103 exons and exon boundaries of the two genes, The P CR products were first scanned for heteroduplexes by conformation-sens itive gel electrophoresis, and then products containing heteroduplexes were sequenced, The results detected disease-causing mutations in 13 of the 15 patients and detected two additional probable disease-causin g mutations in the remaining 2 patients, Analysis of the data develope d in this study and elsewhere revealed common sequences for mutations causing null alleles.