What is the cause of crainiosynistosis?

Either. Caused by either hereditary genetic mutations or the following theories.A possible cell defect in the sutires themselves that leads to early fusion.When in the womb, the baby assumes an irregular position.If pressure was being put on the baby's head, the plates of bone in the skull might be pushed together & caused the sutures to fuse.
Depends. There are different types. The two major types are 1)isolated, when there are no other problems and 2) syndromic, when there are other medical issues (a syndrome). The isolated type has no known cause. Some of the syndromic ones are known to be genetic. Let me know if that's not the kind of answer you were looking for.