It occurs because there is a defect in cells called osteoclasts, which are necessary for the formation of bone marrow. In patients with osteopetrosis, osteoclasts don't work correctly and the cavity for bone marrow does not form. Few blood cells form because of the absence of bone marrow. Other blood-forming organs, particularly the spleen and liver, take over in blood production. As a result, these organs become greatly enlarged.
Bones look solid on X-ray, but are actually brittle.
Abnormal growth results. Patients usually stop growing at age 8 or 10. Occurrence Osteopetrosis is a rare congenital disorder. It strikes in one in every 200,000 children. St. Jude has treated nine patients with this rare disease.