Osteogenesis imperfecta type 2

Osteogenesis imperfecta type 2 (OI type II), also known as perinatally lethal osteogenesis imperfecta or Vrolik disease, is the most severe form of osteogenesis imperfecta, a group of genetic disorders characterized by extreme bone fragility. OI type II is typically lethal in the perinatal period, with most affected infants dying during pregnancy, at birth, or within the first weeks to months of life due to respiratory failure caused by an underdeveloped rib cage and pulmonary hypoplasia. The condition primarily affects the skeletal system but also impacts connective tissues throughout the body. Key clinical features include multiple intrauterine fractures, severely shortened and bowed limbs, a soft and large calvarium (skull), dark blue or gray sclerae (whites of the eyes), extremely low bone mineral density, and a small chest with beaded ribs due to numerous fractures along the rib shafts. The long bones are broad, crumpled, and shortened. Radiographic findings are striking, showing generalized osteopenia, compressed vertebral bodies, and widespread fractures at various stages of healing. OI type II is most commonly caused by heterozygous mutations in the COL1A1 or COL1A2 genes, which encode the alpha chains of type I collagen, the major structural protein of bone, skin, and other connective tissues. These mutations typically result in structurally abnormal collagen rather than reduced collagen quantity. In rare cases, autosomal recessive forms have been identified involving genes such as CRTAP, LEPRE1 (P3H1), and PPIB, which are involved in collagen post-translational modification. Because of the lethal nature of this condition, treatment is primarily supportive and palliative, focusing on comfort care. There are no curative therapies currently available, though prenatal diagnosis through ultrasound and genetic testing allows for early identification and informed family counseling.

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