Osteogenesis imperfecta type II is a lethal type of osteogenesis imperfecta (OI; see this term), a genetic disorder characterized by increased bone fragility, low bone mass and susceptibility to bone fractures. Patients with type II present multiple rib and long bone fractures at birth, marked deformities, broad long bones, low density on skull X-rays, and dark sclera.
The overall prevalence of OI is estimated at between 1/10,000 and 1/20,000 but the prevalence of type II is unknown.
There are three subtypes of OI type II (A, B and C) that are characterized by different radiological features. Patients with OI type IIA present with broad ribs with multiple fractures, continuous beaded ribs and severe undermodeling of the femur, OI type IIB presents with normal or thin ribs with some fractures, discontinuous beaded ribs and some undermodeling of the femur, and OI type IIC presents with varying thickness of the ribs, discontinuous beading of the ribs, malformed scapulae and ischiae, and slender and twisted long bones. Type IIC is extremely rare and its existence is even doubted.
OI type IIA is caused by mutations of the COL1A1 and COL1A2 genes (17q21.31-q22 and 7q22.1 respectively) and transmission is autosomal dominant. Type IIB can be autosomal dominant and also caused by mutations of the COL1A1 and COL1A2 genes (17q21.31-q22 and 7q22.1 respectively) or it can be autosomal recessive and caused by mutations in the CRTAP gene (3p22) (sometimes described as OI type VII) or the LEPRE1 gene (1p34) (sometimes described as OI type VIII) or the PPIB gene (15q21-q22) (sometimes described as OI type IX).
Last update: March 2010