[Update on prenatal diagnosis of osteogenesis imperfecta type II : an index case report diagnosed by ultrasonography in the first trimester].

Introduction: A case of osteogenesis imperfecta type II diagnosed in the first trimester of pregnancy.
Discussion: Lethal osteogenesis imperfecta is a disorder characterized by collagen abnormalities resulting in dwarfism, bone fragility and deformity leading to death in utero or in the perinatal period. Molecular and biochemical studies demonstrate that OI type II results from mutations in either COL1 A1 or COL1 A2 which encode for the chains of type I procollagen. Early diagnosis by US examination in first trimester relies on shortening and bowing of long bones, multiple fractures and hypoechogenicity of the skeleton. When ultrasound examination suspects OI type II, the diagnosis can be accomplished in the first trimester by biochemical analysis if the collagen defect is characterized.
Conclusion: OI type II results mainly from private mutations and parental mosaicism is an important cause of recurrence making genetic counselling difficult.