Osteogenesis imperfecta type 1

Osteogenesis imperfecta type 1 (OI type 1), also known as mild osteogenesis imperfecta or osteogenesis imperfecta with blue sclerae, is the mildest and most common form of osteogenesis imperfecta, a group of inherited connective tissue disorders characterized by bone fragility. It is caused by mutations in the COL1A1 or COL1A2 genes, which encode the alpha chains of type I collagen — the major structural protein of bone, skin, tendons, and other connective tissues. These mutations typically result in a quantitative deficiency of structurally normal type I collagen rather than the production of abnormal collagen seen in more severe forms. Individuals with OI type 1 experience increased bone fragility leading to fractures, often from mild trauma. Fractures may begin in childhood, particularly when the child starts walking, and tend to decrease in frequency after puberty. Characteristic features include distinctly blue or blue-gray sclerae (the whites of the eyes), easy bruising, and mild short stature or normal height. Many affected individuals develop hearing loss, typically beginning in the second or third decade of life, which may be conductive, sensorineural, or mixed. Joint hypermobility is common, and some patients develop mild scoliosis. Dentinogenesis imperfecta (discolored, translucent teeth prone to breakage) may occur but is less common in type 1 than in more severe forms. The skeletal system is the primary system affected, but because type I collagen is widely distributed, the eyes, ears, skin, and dental structures may also be involved. There is currently no cure for OI type 1, but management focuses on minimizing fractures, maximizing mobility, and addressing complications. Bisphosphonates (such as pamidronate or alendronate) may be used to increase bone density and reduce fracture rates, particularly in children. Physical therapy and low-impact exercise are important for strengthening muscles and maintaining bone health. Orthopedic interventions, including intramedullary rodding, may be needed for recurrent fractures or limb deformities. Hearing aids or surgical intervention may be required for progressive hearing loss. Genetic counseling is recommended for affected individuals and their families. With appropriate management, most individuals with OI type 1 have a normal or near-normal life expectancy and can lead active lives.

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