Osteogenesis imperfecta type 5

Osteogenesis imperfecta type 5 (OI type 5) is a rare genetic bone disorder characterized by increased bone fragility and recurrent fractures. It is caused by a specific heterozygous mutation in the IFITM5 gene (also known as BRIL), which encodes a transmembrane protein involved in bone mineralization. OI type 5 is distinguished from other forms of osteogenesis imperfecta by several unique clinical features, including the formation of hyperplastic (hypertrophic) callus at fracture sites, calcification of the interosseous membrane between the radius and ulna in the forearm (which can restrict forearm rotation), and a mesh-like or lamellated pattern seen on bone histology. Unlike many other types of OI, patients with type 5 typically do not have blue sclerae or dentinogenesis imperfecta. The skeletal system is primarily affected, with patients experiencing moderate to severe bone fragility leading to multiple fractures, often beginning in childhood. The hyperplastic callus formation can be dramatic and may sometimes be mistaken for a bone tumor (osteosarcoma). Bone density is generally reduced, and vertebral compression fractures may occur, potentially leading to short stature and skeletal deformity. Joint laxity may also be present in some individuals. There is currently no cure for OI type 5. Treatment is multidisciplinary and focuses on minimizing fractures, maximizing mobility, and managing complications. Bisphosphonate therapy (such as pamidronate or zoledronic acid) is commonly used to improve bone density and reduce fracture frequency, though its effectiveness on hyperplastic callus formation is less clear. Orthopedic interventions, including intramedullary rodding of long bones, may be necessary to correct or prevent deformities. Physical therapy and rehabilitation play important roles in maintaining function and quality of life. Surgical management of the interosseous membrane calcification may be considered if forearm mobility is significantly impaired. Genetic counseling is recommended for affected individuals and their families.

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