Osteogenesis imperfecta

Osteogenesis imperfecta is a group of inherited connective-tissue disorders marked chiefly by fragile bones. Most cases involve defects in the production or processing of type I collagen.

Type I collagen: The main structural collagen in bone, skin, tendons, and several other connective tissues. Its abnormal quantity or structure underlies most forms of osteogenesis imperfecta.
Autosomal dominant inheritance: A pattern in which one altered copy of a gene can cause a trait or disorder. Many cases are inherited this way, though new variants also occur.
Bisphosphonate: A class of drugs that reduces bone resorption by osteoclasts. These drugs are used in some patients to improve bone density and reduce fracture burden.
Sillence classification: A clinical system that groups osteogenesis imperfecta into types based largely on severity and features. It provides the familiar types I through IV, though the genetic spectrum is broader.
COL1A1: A gene encoding the pro-alpha1(I) chain, one of the two chains in type I collagen. Many cases result from variants that reduce or alter this collagen chain.
De novo mutation: A genetic variant that arises newly in an individual rather than being inherited from a parent. A substantial number of affected people have no family history because of a new variant.
Intramedullary rod: A metal implant placed inside a long bone to stabilize it. Rodding can support deformed or repeatedly fractured long bones.
Osteoporosis: A skeletal disorder characterized by reduced bone strength and increased fracture risk. Both conditions cause fragility, but osteoporosis is not defined by inherited collagen defects.
COL1A2: A gene encoding the pro-alpha2(I) chain of type I collagen. Variants can disrupt collagen structure and cause several forms of the disorder.
Bone matrix: The extracellular material of bone, consisting mainly of collagen and mineral crystals. Fragility reflects defects in the framework that normally supports bone mineral.

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