Osteogenesis Imperfecta

Osteogenesis imperfecta is a general bone disease with a triad of clinical features: multiple fractures, blue sclerae and conductive hearing loss. There is a congenital recessive form in newborns that is often rapidly fatal and a tardive one in adults that is inherited as a mendelian dominant and is more benign. Mutations of type I collagen genes have been established as the underlying cause leading to a general disturbance in the development of collagen, hence the thin sclerae appearing blue as well as poorly formed bone tissue.

In the long bones the resorption of cartilage in the development of bone is normal, but the bony trabecu-lae themselves are poorly formed and the same may be seen in the temporal bone [46]. The ossicles in the tardive form are very thin and subject to fractures. The stapes footplate is also frequently fixed. The disturbance in lamellar bone formation can lead to extreme thinness, dehiscence, and non-union of the stapedial superstructure with the footplate, or thickening with fixation of the footplate. The nature of the bony tissue causing this fixation is problematical. It has been suggested that osteogenesis imperfecta can be associated with otosclerosis so that the fixation is indeed otosclerotic [28]. Otosclerosis, like osteogenesis imperfecta, may indeed be part of a general connective tissue disturbance [4].

Indeed, some cases of clinical otosclerosis may be related to mutations within the COL1A1 gene that are similar to those found in mild forms of osteogenesis imperfecta [63].

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