What are the types of Osteogenesis Imperfecta?

Type I OI

• most common and mildest type of OI
• bones predisposed to fracture (most fractures occur before puberty)
• normal or near-normal stature
• loose joints and muscle weakness
• blue, purple, or gray tint to sclera (whites of the eyes)
• triangular face
• tendency toward spinal curvature
• absent or minimal bone deformity
• possible brittle teeth
• possible hearing loss, often beginning in early twenties or thirties
• normal collagen structure, but less than normal amount

Type II OI

• most severe form of OI
• frequently causes death at birth or shortly after, because of respiratory problems
• numerous fractures and severe bone deformity
• small stature with underdeveloped lungs
• blue, purple, or gray tinted sclera
• improperly formed collagen

Type III OI

• easily fractured bones (Fractures often present at birth, and x rays may reveal healed fractures that occurred before birth.)
• small stature
• blue, purple, or gray tinted sclera
• loose joints and poor muscle development in arms and legs
• barrel-shaped rib cage
• triangular face
• spinal curvature
• possible respiratory problems
• often severe bone deformity
• possible brittle teeth
• possible hearing loss
• improperly formed collagen

Type IV OI

• between Type I and Type III OI in severity
• bones easily fractured (most fractures occur before puberty)
• smaller than average stature
• sclera normal in color (i.e., white or near-white)
• mild to moderate bone deformity
• tendency toward spinal curvature
• barrel-shaped rib cage
• triangular face
• possible brittle teeth
• possible hearing loss
• improperly formed collagen
• By studying the appearance of OI bone under the microscope, investigators 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 people, they found the groups had other features in common. They named these groups Type V and Type VI OI. The mutations causing these forms of OI have not been identified, but people in these two groups do not have mutations in the type 1 collagen genes.

Type VI OI

• clinically similar to Type IV OI in appearance and symptoms
• slightly elevated activity level of alkaline phosphatase (an enzyme linked to bone formation), which can be determined by a blood test
• distinctive “fish-scale” appearance to bone when viewed under the microscope
• diagnosed by bone biopsy
• unknown whether this form is inherited in a dominant or recessive manner, but researchers believe the mode of inheritance is most likely recessive
• eight people identified with this type of OI to date