We don't know what causes Paget's disease. But genetic factors and viruses may play a role.

• Genetics. If your parents, brothers, or sisters have Paget's disease, you are more likely to develop the disease than if you do not have a family history of the disease.¹
• Virus. Viruses have been found in the bones of people with Paget's disease. The viruses may be associated with measles and canine distemper (found in dogs).² But there is no proof that any of these viruses cause Paget's disease.