Osteogenesis imperfecta (OI), also called Brittle Bone Disease, is a genetic protein deficiency that results in fragile bones. The protein affected is usually Type-I collagen. The disorder is typically a dominant genetic trait that is passed through the parents, but it may also be a de novo mutation, with no family history. There are also two rare and recently discovered forms of osteogenesis imperfecta that are recessive genetic traits.

There are currently eight recognized types of osteogenesis imperfecta, ranging from the mild to the fatal. Most types result in deformities. In Type I OI, collagen is of normal quality, but there is not enough produced. This is the mildest type, though the bones are still easily broken. Other symptoms include discoloration of the sclera or whites of the eyes, early hearing loss, slightly protruding eyes, slight curvature of the spine, loose joints, and poor muscle tone.

Type II OI is the most severe form, in which collagen is of insufficient quality and quantity. Deformities and respiratory problems are severe, and most cases die within the first year of life.

In types III, IV, V, and VI OI, collagen is produced in normal quantities, but its quality is poor. Sufferers of Types III, IV, V, and VI OI are characteristically short in stature, with a curved spine and a barrel-shaped rib cage. Type III is distinguished by being progressive; deformities and other symptoms may be slight at birth but develop over time.

The symptoms of Type III OI are similar to those of other types, but more severe. Serious bone deformities may present, and bones may break even before birth. Respiratory problems are also possible.

Types IV, V, and VI OI share the same clinical features. Deformities are mild to moderate, often accompanied by discolored sclera and early loss of hearing. The risk of bone fractures is highest before puberty. Type V is characterized by a "mesh-like" appearance of the bones, while the bones of a person with Type VI have a "fish scale" appearance.

Osteogenesis imperfecta is an incurable condition. Treatments to manage the disease include surgery, physical therapy, and physical aids. Bone infections are managed with antibiotics and antiseptics when they occur. Medication, either oral or intravenous, is also used to treat osteogenesis imperfecta. Bisphosphonates are most widely used for this condition. Clinical trials have evaluated the efficacy of Fosamax, currently used to treat osteoporosis, for osteogenesis imperfecta. However, the long-term effects of such treatment are unknown, and the United States Food and Drug Administration has not yet approved the drug for osteogenesis imperfecta.