Fifty-four patients were found to have COL1A1/2 mutations, 33 with COL1A1 and 21 with COL1A2; this equated to 36.3 and 23.1 % of patients, respectively, totaling 59.4 % of the studied OI cases exhibiting collagen type I mutations. This evidence concerns the gene COL1A1 and osteogenesis imperfecta.