| Osteogenesis Imperfecta Type III |
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OI Type III is the most severe type among children who survive the neonatal period.
The degree of bone fragility and the fracture rate vary widely.
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This type is characterized by structurally defective type I collagen. This poor quality
type I collagen is present in reduced amounts in the bone matrix.
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At birth, infants generally have mildly shortened and bowed limbs, small chests, and
a soft calvarium. Respiratory and swallowing problems are common in newborns.
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There may be multiple long-bone fractures at birth, including many rib fractures.
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Frequent fractures of the long bones, the tension of muscle on soft bone, and
the disruption of the growth plates lead to bowing and progressive malformation.
Children have a markedly short stature, and adults are usually shorter than 3 feet,
6 inches, or 102 centimeters.
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Spine curvatures, compression fractures of the vertebrae, scoliosis, and chest
deformities occur frequently.
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The altered structure of the growth plates gives a popcorn-like appearance to the
metaphyses and epiphyses.
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The head is often large relative to body size.
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A triangular facial shape, due to overdevelopment of the head and underdevelopment
of the face bones, is characteristic.
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The sclerae may be white or tinted blue, purple, or gray.
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Dentinogenesis imperfecta is common but not universal.
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The majority of OI Type III cases result from dominant mutations in type I collagen
genes. Often these mutations are spontaneous. Similar extremely severe types of OI,
Types VII and VIII, are caused by recessive mutations to other genes.
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Genetic counseling is recommended for asymptomatic parents of a child with OI Type III
before any future pregnancies.
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Significant care issues that arise with OI Type III include the need to prevent fracture cycles;
the appropriate timing of rodding surgery; scoliosis monitoring; respiratory function monitoring;
the need to develop strategies to cope with short stature and fatigue; the family’s need for
emotional support, especially during infancy; and the off-label use of bisphosphonates.
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It is also important to address difficulties with social integration, participation in leisure activities,
and maintaining stamina.
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The treatment plan should maximize mobility and function, increase peak bone mass and muscle strength, and employ as much exercise and physical activity as possible.
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