Hi , thanks for reaching out! This is a great question. Both parents have to be carriers in order for the child to be affected by cystic fibrosis. Here's some more detailed information about what it means to be a carrier if you'd like to read more - https://cystic-fibrosis.com/clinical/carrier/ Hope that helps, and thank you again for reaching out.
- Shelby, Cystic-Fibrosis.com Team Member