Familial Alzheimer disease is a rare autosomal dominant disorder that is caused by one of three genes on chromosome 21. Because it is autosomal dominant and rare, it can be assumed that the father does not have the disorder. Therefore, each child has a 50% chance of having inherited the gene responsible for FAD. It is not an X-linked disorder, so it is not limited to the male children. As an autosomal dominant disorder, there are no carriers – they either have the affected gene or do not.