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KEY POINTS
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Key Points

  • Clinically and genetically heterogeneous disorder manifested by bone fragility and low bone mass.

  • Seven distinct subtypes exist. Severity is as follows: type II > type III > types IV = V = VI = VII > type I.

  • Most cases that present prenatally are types II or III. Only 10% of fetuses with type I have fractures in utero.

  • Other findings include blue sclerae, abnormal teeth, joint hyperlaxity, adult-onset hearing loss, and normal intelligence.

  • Prenatal sonographic findings include long bone fractures with callus formation, limb shortening, poor mineralization of the skull, and bent femurs.

  • Differential diagnosis includes campomelic dysplasia, hypophosphatasia, and achondrogenesis.

  • In 90% of cases there is a mutation in one of the genes that codes for type I procollagen, COL1A1 or COL1A2.

  • Most cases are dominantly inherited. If parents are asymptomatic there is a 7% recurrence risk due to the surprisingly high incidence of gonadal mosaicism.

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CONDITION
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Osteogenesis imperfecta is a clinically and genetically heterogeneous disorder of connective tissue, manifested by bone fragility and low bone mass. Affected patients have blue sclerae, hearing abnormalities, defective dentition, hyperlaxity of the joints, and normal intelligence (Brons et al., 1988). The majority of affected individuals are heterozygous for mutations of the COL1A1 or COL1A2 gene, which alters the structure of type I procollagen (Cole and Dalgleish, 1995).

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Osteogenesis imperfecta was originally classified into four clinically distinct disorders that were first delineated by Sillence et al. (1979), and modified by Rauch and Glorieux (2004) (Table 91-1). Type I is the common mild form, type II is the perinatal lethal form, type III is the severe form, and type IV is the moderately clinically severe form (Cole and Dalgleish, 1995). More recently, an additional three types (V, VI, and VII) have been described (Rauch and Glorieux, 2004). The clinical severity of OI is type II > type III > types IV = V = VI = VII > type I.

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Table Graphic Jump Location
Table 91-1Expanded Sillence Classification of Osteogenesis Imperfecta

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