A child who inherits the abnormal CF gene from both parents does not produce a certain protein. This protein is necessary for the transport of chloride and water through the mucous membrane cells of organs such as the lungs, pancreas, liver, and intestines.
You can only have CF if both parents carry the CF gene. One in 32 Dutch people is a carrier of the defective CF gene. If both parents have this gene, the child has a 25% chance of having cystic fibrosis. This chance is the same for every pregnancy. Carriers, by the way, are not sick. Testing for carrier status is possible.