Osteogenesis imperfecta comprises a group of conditions which result in several different types of limb shortening (often micromelic) and dwarfism. The underlying cause is a defect in type I collagen synthesis resulting in skeletal, ligament, skin, sclera, and dentin abnormalities. Either too little normal collagen or variable quantities of abnormal collagen are produced.  The majority of cases are autosomal dominant in transmission, with approximately 25 % due to spontaneous mutations. The incidence is between 1 and 20,000 to 60,000 births. Four types of osteogenesis imperfecta exist:

• Type I ("Tarda")
  • Most common and mildest form, autosomal dominant
  • Mildly fragile bones which may fracture at delivery
  • May have short stature
  • Loose joints
  • Blue sclerae
  • Brittle teeth
  • Hearing loss, beginning in the second decade of life
  • Normal collagen structure, but produced in abnormally low amounts
• Type II ("Congenita")
  • Most severe form, autosomal recessive/sporadic
  • Usually lethal at birth
  • Severely fragile bones, fractures in utero
  • Small stature with short limbs
  • Abnormal collagen
• Type III
  • Known as severe progressively deforming osteogenesis imperfecta
  • May be autosomal dominant
  • Abnormal collagen
  • In utero fractures
  • Short stature, loose joints
  • Barrel rib cage, triangular face
  • Spinal curvature
  • May live into adulthood

• Type IV ("Tarda")
  • Autosomal dominant
  • Little tendency to develop hearing loss
  • Femoral bowing, only a mild bone deformity
  • Short stature
  • Abnormal collagen
  • Near normal sclera

Care of fractures, extensive surgical and dental procedures, and physical therapy are often recommended for people with osteogenesis imperfecta. Specifically, bone marrow transplants and bisphosphonate therapy have been studied to increase bone mass, the main source of morbidity.

REFERENCES

• Niyibi C, Smith P, Mi Z, Robbins, P, Evans C. Potential of gene therapy for treating osteogenesis imperfecta.
  Clin Orthop. 2000 Oct;(379 Suppl):S126-33.
• Antoniazzi F, Mottes M, Fraschini P, Brunelli PC, Tato L. Osteogenesis imperfecta: practical treatment guidelines.
  Paediatr Drugs. 2000 Nov-Dec;2(6):465-88.

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