Can Alagille syndrome be inherited from a parent who has the syndrome?
If a parent has Alagille syndrome, they can pass it on to their children. There is a 1 in 2, or 50%, chance of each child having Alagille syndrome. That does not mean that half of the parent's children will have Alagille syndrome, but that each child has a 50% chance of inheriting it. About 30-50% of children with Alagille syndrome have a parent with the condition. In other cases, it may be that the child affected with the condition is the first person in the family to have the gene change.
Alagille Syndrome. Genetics Home Reference. https://ghr.nlm.nih.gov/condition/alagille-syndrome