Doctors don't really know what causes Paget's disease. It may be a viral infection of the bone, or it could be caused by something in the environment. In about 15% to 30% of cases, there's a family history of Paget's. Researchers have found a few genes that can make it more likely that you or a family member will get it. Smoking may also increase your chances.
If you have family members with it, you should get a blood test every 2 to 3 years after age 40.