OI (osteogenesis imperfecta)

Osteogenesis imperfecta is a group of diseases where there is an increased fragility of bone with frequent fractures. They are all associated with type I collagen mutations.

• affected patients are prone to fragility fractures from the mildest trauma, according to the variable severity of the condition
• other common clinical features include
  • progressive skeletal deformities
  • varying degrees of short stature
  • blue sclerae
  • dentinogenesis imperfecta
  • joint laxity
  • onset of deafness in adulthood
• estimated prevalence is 1 in 10 000 to 1 in 20 000 births
• nearly all OI cases are due to heterozygosity of dominant mutations in one or other of the two genes (COL1A1 and COL1A2) that encode for type I procollagen chains (1)
  • these type 1 procollagen chains form type I collagen, the major structural protein of the extracellular matrix of bone, skin and tendons
    • there have been more than 200 mutations identified so far
    • some mutations give rise to a qualitative type I collagen defect caused by a structural alteration of the collagen molecule. Other mutations maintain the synthesis of normal collagen, but in reduced quantity
      • mutations resulting in qualitative changes in type I collagen generally lead to the most severe forms of OI
      • Sillence et al. (1) have classified the condition into four major subtypes

The four main types of osteogenesis imperfecta are briefly summarized in this section of the database.

Physiotherapy, rehabilitation, and orthopedic surgery are the mainstays of treatment in moderate to severe forms of osteogenesis imperfecta . Also medical treatment with bisphosphonates can bring significant additional improvements (3)

Notes:

• with respect to classification of osteogenesis imperfecta
  • broad clinical and biomolecular spectrum mean that any classification is unable to be complete or accurate - however it represents a practical tool for the clinician dealing with management of patients

Reference:

1. Devogalaer JP. New uses of bisphosphonates: osteogenesis imperfecta. Curr Opin Pharmacol. 2002 Dec;2(6):748-53.
2. Sillence D et al.Genetic heterogeneity in osteogenesis imperfecta. J Med Genet 1979;16:101–116.
3. Rauch F, Glorieux FH. Osteogenesis imperfecta, current and future medical treatment. Am J Med Genet C Semin Med Genet. 2005.