Paget's disease of bone is a progressive bone disease that doesn't have a known cause. It's thought to be inherited. This means that it's passed from parent to child and is caused by a gene in your genetic make-up which either makes you more susceptible to developing it or the symptoms show themselves as you get older. There is, however, no clear pattern of inheritance. So, if you have it, that doesn't mean that your children will too.
Attribution: BUPA