These conditions are mostly inherited in an autosomal dominant pattern, which means that one copy of the altered gene is sufficient to cause the condition.
Occasionally, the condition can be inherited in an autosomal recessive pattern, where a faulty copy of the gene will need to be inherited from each parent in order for the condition to develop. For more information, see our factsheet: Inheritance and genetics.)
In some cases, there is no previous family history and the condition is caused by a new mutation.