Osteogenesis imperfecta type 4

Osteogenesis imperfecta type 4 (OI type IV), also known as moderate osteogenesis imperfecta or Sillence type IV, is a genetic connective tissue disorder characterized by bone fragility that is moderate in severity, falling between the milder type I and the more severe types II and III. 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. Defective collagen production leads to bones that fracture easily, often from minimal trauma or even normal daily activities. Key clinical features include recurrent fractures (which may be present at birth or develop in early childhood), short stature that is variable in degree, bowing of the long bones, mild to moderate skeletal deformity, and dentinogenesis imperfecta (abnormal, discolored, and fragile teeth) in some individuals. Unlike OI type I, scleral color in type IV is typically normal or near-normal (white or slightly grayish), which is an important distinguishing feature. Hearing loss may develop in adolescence or adulthood. Joint hypermobility and easy bruising can also occur. The skeletal system is primarily affected, but because type I collagen is widespread, the eyes, teeth, skin, and auditory system may also be involved. Treatment is multidisciplinary and focuses on maximizing mobility, preventing fractures, and managing complications. Bisphosphonate therapy (such as intravenous pamidronate or zoledronic acid) is commonly used to increase bone mineral density and reduce fracture frequency, particularly in children. Orthopedic interventions, including intramedullary rodding of long bones, may be necessary to correct bowing and prevent recurrent fractures. Physical therapy and rehabilitation are essential components of care. Dental management is important for those with dentinogenesis imperfecta. While there is no cure, advances in medical and surgical management have significantly improved quality of life and functional outcomes for individuals with OI type IV.

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