What chance do males have to pass the Fragile X gene mutation to their children?

Because males have only one X chromosome, fathers who carry the premutation will pass it on to all their daughters and none of their sons (they pass their Y chromosome on to their sons). There have been no reports of premutations that are passed from a father to his daughter expanding to a full mutation. 

We recommend you work with a genetic counselor and your healthcare provider to review inheritance patterns.

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