Cystic Fibrosis About 1 out of 201 Caucasian people carries at least one of the fatal defective genes that cause cystic fibrosis, CF, or mucoviscidosis (in Europe) although carriers don't show any signs of the disease. Therefore, 10 million people carry the defective gene and aren't aware of it. This makes it one of the most common genetic defect in the United States. CF is a recessive gene. That means that it may, but doesn't always skip generations. In order to get this disease, both parents must be carriers. If one parent has CF and the other one is not a carrier than there is a 100% chance that their child