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CHAPTER 14
Osteogenesis Imperfecta
CHAPTER OBJECTIVES
- Describe the etiology and various forms of osteogenesis imperfecta.
- Detail the symptoms associated with osteogenesis imperfecta.
- Discuss the diagnostic criteria of osteogenesis imperfecta.
- Review current surveillance and treatment recommendations for osteogenesis imperfecta.
KEY TERMS
Osteogenesis imperfecta (OI) is a group of genetic disorders that affect the development of bones. Specifically, mutations in the genes that are normally responsible for the coding of proteins for collagen type I are compromised, leading to the weakening of connective tissue, especially bones. Fractures may occur in any bone in the body but most commonly appear in one of the extremities. The occurrence of fractures leads to the varying conditions that are more plainly referred to as brittle bone disease. The disease is classified based on severity, with eight current forms categorized as osteogenesis imperfecta I–VIII. This classification differs from a logical progression of disease, however; type I is the mildest of the forms, type II is the most severe, and types III–VIII are varying combinations of type II and type I. Advancing genetics has played a key role in the ability to classify the various forms of the disease. OI is known to have different autosomal dominant inheritance patterns of type I collagen. These are known as OI types I, II, III, IV, and V. OI may also be inherited in a recessive manner (types VII and VIII). Types V and VI are not associated with type I collagen mutation, although their gene origin is unknown (Table 14-1).
KEY TERM
Osteogenesis imperfecta (OI): comes from the increasing likelihood of fracture from seemingly minor injuries or, in some cases, with no apparent cause at all.
Varying Types of Osteogenesis Imperfecta and Their Features |
Type | Characteristics |
I | Most common type and mildest Predisposed to fracture (most before puberty); normal or near normal stature; loose joints; muscle weakness; triangular face; tendency of spinal curvature; absent to minimal bone deformity; possible dentinogenesis imperfecta; possible hearing loss, often occurring in early 20s or 30s; normal collagen structure but less in quantity. |
II | Most severe form of OI Numerous fractures and severe bone deformity; perinatal mortality or mortality shortly after birth due to respiratory issues; very short stature; underdeveloped lungs; blue-, purple-, or gray-tinted sclera; improperly formed collagen. |
III | The most severe type among those who survive the neonatal period Bones that fracture easily may present at birth, or healed fractures may show in the womb. Other characteristics include short stature; blue, purple, or gray sclera; loose joints; poor muscle development in the arms and legs; triangular face; spinal curvature; severe bone deformity; possible respiratory problems; possible dentinogenesis imperfecta; possible hearing loss; improperly formed collagen. |
IV | Between types III and I in severity Bones fracture easily (most often before puberty); small in stature; normal sclera; mild to moderate bone deformity; triangular face; possible tendency of spinal curvature; possible dentinogenesis imperfecta; possible hearing loss; improperly formed collagen. |
V | Similar to type IV Dense band seen on x-rays adjacent to the growth plates on long bones; unusually large calluses (hypertrophic calluses) at the site of fractures or surgical procedures; calcification of the membrane between the radius and the ulna, which leads to restriction of forearm rotation; normal sclera; normal teeth with “meshlike” appearance to bone when viewed under a microscope. |
VI | Similar to type IV; extremely rare Elevated alkaline phosphatase activity; bone has a “fish scale” appearance under a microscope. |
VII | Similar to type IV in the first documented cases Short humerus and femur; small stature; coxa vara. |
VIII | Resembles lethal type II or type III OI, except infants have white or near-white sclera Severe growth deficiency; extreme skeletal undermineralization. |
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