What causes cystic fibrosis?

Cystic fibrosis, a genetic disorder, is present from birth.

CF occurs when a child inherits two defective copies of the gene responsible for CF, one from each parent.

Approximately one in 25 Canadians is a CF carrier, carrying only one defective version of the gene responsible for cystic fibrosis. Carriers do not have, and can never get, cystic fibrosis. In most cases, they are not even aware they are carriers until they have a child with CF.

When two carriers have a child, there is a

• 25% chance the child will be born with cystic fibrosis
• 50% chance the child will not have CF, but will be a carrier
• 25% chance the child will not have CF and will not be a carrier

With each pregnancy, the risks are exactly the same. Two carrier parents may have several children with cystic fibrosis or none at all. For more information, visit:

Starting a Family
Carrier Testing for Cystic Fibrosis
Cystic Fibrosis Animated

Reviewed/updated: 2011-07-26