How Is Cystic Fibrosis Inherited?

Introduction

Cystic fibrosis, or CF, is a serious illness that causes respiratory failure and vitamin deficiencies. CF affects the secretions of the body: saliva, mucus, sweat and digestive juices. Instead of being thin and watery to lubricate the body, in cystic fibrosis, these secretions are sticky and thick. The secretions clog up the passageways in the body and causes damage to the pancreas and lungs. This life-threatening disease is caused by inheriting defective genes from both parents.

The Gene

Cystic fibrosis is caused by a defective gene that changes a protein responsible for the movement of salt into and out of each cell. According to the Mayo Clinic, "This results in thick, sticky secretions in the respiratory and digestive tracts, as well as in the reproductive system." This gene is a recessive gene, meaning that, for a person to inherit this defective gene, he must get a copy of it from both parents. If only one parent has the gene, a child cannot inherit cystic fibrosis. If a child has one copy of the gene, she can be a carrier of the disease. As a carrier, a person has the potential to pass the defective gene on to his offspring.

The Odds of Inheriting Cystic Fibrosis

There is no guarantee that if two people with the recessive gene conceive a child, their offspring will get the disease. According to the Mayo Clinic, there is a 25 percent chance that their child will be born with cystic fibrosis. There is a 25 percent chance that the child will not inherit the disease and also not be a carrier of the disease. There is a 50 percent chance that the child will have the recessive gene.

The Carriers

People who have the recessive gene lead healthy lives. They have no symptoms of the disease. In many cases, they are not even aware that they have the cystic fibrosis gene. But genetic testing is now available to identify those who have the gene. The cystic fibrosis carrier test can be done in a doctor's office. If cystic fibrosis runs in your family, it is a good idea to be tested along with your partner to see if you both carry the gene. The test is performed on a sample of blood or saliva. But this test is not 100 percent accurate. The Mayo Clinic reports that in some cases, "genetic mutations for cystic fibrosis can't be detected by the current test." What this means is that, in rare situations, the test will give a normal result but a person may still be a carrier.