Osteogenesis imperfecta type I - mild disease

Type I ostoegenesis imperfecta is the commonest and mildest form, with features as follows:

• inherited in an autosomal dominant manner
• presentation is in childhood
• fractures occur throughout life
• deformity is rare

This type of osteogenesis imperfecta is caused by abnormal or decreased synthesis of pro-alpha1 or pro-alpha2 collagen polypeptides.

Notes:

• nearly all osteogenesis imperfecta (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 name
  • the 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