Osteogenesis imperfecta

The general term given to a heterogeneous group of inherited disorders of collagen, caused by mutations of one of the two genes encoding collagen type 1, COL1A1 and COL1A2. Predominant features are osteopenia, multiple fractures, severe bony deformities, and short stature. Four broad types have been identified, but increased knowledge of the large number of genetic mutations suggests that further expansion of groupings will be needed (Cole & Cohen 1991,Marini 1998). In less severe cases, diagnosis may be delayed, but the resultant bony fragility, and propensity to fractures, may result in the mistaken diagnosis of child abuse (Gahagan & Rimsza 1991). In severe cases, cardio-respiratory failure and basilar invagination of the skull are the most frequent causes of death. Anaesthesia may be required for reduction of fractures, scoliosis surgery, neurosurgery, and other corrections of skeletal deformities.

Type I is of autosomal dominant inheritance and present in 80% of cases. Extraskeletal tissues are mainly involved and the bone disease is mild. Fractures mainly occur in childhood but become less common after puberty. The joints are hypermobile, and the tendons susceptible to rupture. Patients are almost normal in stature. The sclera are blue, 50% have early-onset deafness and only some children have dental problems.The aortic valve is thin, and sometimes incompetent.

Type II have severe skeletal abnormalities and usually die in the perinatal period.

Type III have severe skeletal deformities that are progressive. Chest deformity, with kyphoscoliosis and prominent sternum, often results in respiratory problems. Long bones are narrow and bent.The skull is large and asymmetrical and there may be cortical atrophy. Sclera are usually white, but can be blue in childhood. Dentinogenesis imperfecta is frequent. Hearing defects are common.

Type IV is similar to type I, but with more bone abnormalities and some dwarfing.Teeth are frequently involved. Sclera are white.

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