Osteogenesis imperfecta (OI) is a term for a group of genetic diseases in which the bones are formed improperly, making them fragile and likely to break. This happens when collagen, the fibrous protein material that makes up skin, bone, cartilage, and ligaments, is faulty.

Osteogenesis imperfecta affects equal numbers of males and females. It occurs in about one of every 30,000 births. Osteogenesis imperfecta is a genetic disorder, but not everyone who has it received a defective gene from his or her mother or father. Some cases are due to a spontaneous mutation (a permanent defect in a specific gene) that occurs after birth. A person who has osteogenesis imperfecta due to a spontaneous mutation can then pass on this defective gene to his or her future offspring.

There are four forms of osteogenesis imperfecta, called Types I through IV. Of these, Type II tends to be...