An Introduction to the Types of Osteogenesis Imperfecta
In 1979, Sillence and others devised a classification scheme that divides
osteogenesis imperfecta (OI) into four types (two additional types have subsequently been added). Features of osteogenesis imperfecta vary not only between types but within each type as well. Patients with OI may correlate with some, but not all, of the clinical features.
Children and adults with milder osteogenesis imperfecta may have few obvious signs. Some patients appear to have characteristics of several types. Patients may walk unassisted; require the assistance of walkers, crutches, or braces; or be wheelchair-dependent. The frequency of fractures may decrease after puberty. An increase in fractures may be seen in women following
menopause and in men during later life.
Specific Types of Osteogenesis Imperfecta
Specific types of osteogenesis imperfecta include:
- Type I
- Type II
- Type III
- Type IV
- Type V
- Type VI.
Type 1 (Type I) Osteogenesis Imperfecta
Type I osteogenesis imperfecta is the most mild type of OI. Some features of this type of osteogenesis imperfecta include:
- Bones predisposed to fracture; most fractures occur before puberty
- Normal or near-normal stature
- Loose joints and muscle weakness
- Sclera (whites of the eyes) usually have a blue, purple, or gray tint
- Triangular face
- Tendency toward spinal curvature
- Bone deformity absent or minimal
- Brittle teeth possible
- Hearing loss possible, often beginning in early 20s or 30s
- Collagen structure is normal, but the amount is less than normal.
Type 2 (Type II) Osteogenesis Imperfecta
Type II osteogenesis imperfecta is the most severe form of osteogenesis imperfecta. Some features of this type of the disorder include:
- Frequently lethal at or shortly after birth, often due to respiratory problems; in recent years, some people with type II have lived into young adulthood
- Numerous fractures and severe bone deformity
- Small stature with underdeveloped lungs
- Collagen improperly formed.
Type 3 (Type III) Osteogenesis Imperfecta
Type III osteogenesis imperfecta is the most severe form of OI in people who survive the perinatal period. Some features of this type of OI include:
- Bones fracture easily; fractures often present at birth, and x-rays may reveal healed fractures that occurred before birth
- Short stature
- Sclera (whites of the eyes) have a blue, purple, or gray tint
- Triangular face
- Spinal curvature
- Loose joints and poor muscle development in arms and legs
- Brittle teeth possible
- Respiratory problems possible
- Bone deformity, often severe
- Barrel-shaped rib cage
- Hearing loss possible
- Collagen improperly formed.
Type 4 (Type IV) Osteogenesis Imperfecta
Type IV osteogenesis imperfecta is between type I and type III in severity. Some features of this type of osteogenesis imperfecta include:
- Bones fracture easily, most before puberty
- Shorter than average stature
- Barrel-shaped rib cage
- Triangular face
- Sclera are white or near-white (i.e., normal in color)
- Hearing loss possible
- Mild to moderate bone deformity
- Tendency toward spinal curvature
- Brittle teeth possible
- Collagen improperly formed.
Type 5 (Type V) and Type 6 (Type VI) Osteogenesis Imperfecta
For a number of years, investigators have been conducting special studies on the appearance of OI bone under the microscope. They noticed that some people who are clinically within the type IV group had a distinct pattern to their bone. When they reviewed the full medical history of these individuals, they found that groups had other features in common. They named these groups types V and VI OI. Patients in these two groups do not have evidence of having mutations in the type I collagen genes.
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