Osteogenesis imperfecta, also known as brittle bone disease, is a genetic disease that affects 20,000 to 50,000 people in the United States, according to the National Institute of Arthritis and Musculoskeletal and Skin Diseases. There are eight types of brittle bone disease classified by how they are inherited. Most of the types, about 85 to 90 percent as reported by NIAMS, are passed from parent to child by a dominant mutation in the gene that codes for type I collagen. Because collagen is a fibrous protein found in bones, cartilage, tendons and other connective tissues, most of the resulting symptoms of brittle bone disease are related to the bones and joints.
Fractures
Bones are complex structures made up of proteins, minerals and living cells. The foundation of bones is formed by collagen proteins binding together to form strong fibrous rods. The minerals are then deposited on this strong foundation.
In those with brittle bone disease, either not enough collagen is produced or that which is produced is deformed. As a result, the collagen rods are weak and misshapen. This type of bone easily breaks, especially in children whose bones are rapidly growing.
Joint Laxity
Joint laxity is the lack of stability in a joint, which is where two bones come together. Joints are made up of the two bones involved along with the cartilage, tendons and ligaments that hold everything together. Cartilage, tendons and ligaments all consist of collagen. The defective collagen produced in those with brittle bone disease results in cartilage, tendons and ligaments that do not function properly, resulting in the joint laxity.
Blue Sclera
The sclera is the fibrous membrane that, along with the cornea, covers the eye and provides protection. The portion of the sclera that can be seen is often referred to as the white of the eye. The sclera contains collagen. Because of the dysfunction of the production of type I collagen in those with brittle bone disease, the sclera is thinner than normal. This allows the veins in the eye to show through, giving the sclera a blue color.
Hearing Loss
About 50 percent of all those with brittle bone disease experience hearing loss, as reported by the Osteogenesis Imperfecta Foundation. The ability to hear requires sound waves to be translated into movement by the three small bones in the middle ear. If one of these bones fracture, hearing loss can occur.
Chronic Pain
Chronic pain is a symptom that many adults with brittle bone disease report as significant. The pain, often in the lower back or hips, may be due to old fractures or to compression fractures in the spine. Joint pain may also be prevalent as the joints already affected by the disease experience wear due to age.
