Albers-Schönberg osteopetrosis

Albers-Schönberg osteopetrosis, also known as autosomal dominant osteopetrosis type II (ADO2) or marble bone disease, is the most common form of osteopetrosis. It is a genetic skeletal disorder characterized by increased bone density due to defective osteoclast-mediated bone resorption. Although osteoclasts are present, they fail to resorb bone effectively, leading to abnormally dense but structurally fragile bones. The condition is caused primarily by mutations in the CLCN7 gene, which encodes a chloride channel essential for osteoclast acidification of the resorption lacuna. The disease predominantly affects the skeletal system but can have secondary effects on the hematologic and neurological systems. Key clinical features include generalized osteosclerosis (increased bone density visible on X-rays), pathological fractures despite dense-appearing bones, hip osteoarthritis, scoliosis, and cranial nerve compression — particularly affecting the optic and facial nerves, which can lead to visual impairment or facial palsy. Some patients may experience bone pain, osteomyelitis (especially of the mandible), and delayed fracture healing. The classic radiographic finding is the "bone-within-a-bone" appearance and a "rugger jersey" spine with endplate sclerosis of the vertebral bodies. Bone marrow space may be reduced, occasionally leading to mild anemia. Albers-Schönberg disease is generally considered a benign form of osteopetrosis compared to the severe autosomal recessive infantile forms, and many affected individuals may remain asymptomatic or mildly affected throughout life. Clinical expressivity is highly variable, even within the same family. There is currently no cure for this condition. Treatment is primarily supportive and symptomatic, including orthopedic management of fractures, surgical decompression for cranial nerve involvement, dental care to prevent or manage osteomyelitis, and monitoring for hematologic complications. Unlike the severe infantile forms, hematopoietic stem cell transplantation is generally not indicated for ADO2.

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