Genetic Testing and Diagnosis of Cystic Fibrosis

Prospective parents who have a history of cystic fibrosis in their family may want to consider DNA testing before starting or adding to their family. Cystic fibrosis is an inherited disease that can only be passed on to the child if both parents are carriers of the mutant gene that causes cystic fibrosis. If only one parent is a carrier but shows no signs of the disease the child has a 25 percent chance of also being a carrier of the gene.

DNA analysis involves screening molecules found in the DNA to look for the carrier gene. The gene is associated with the number seven chromosomes. There are over 900 mutations of the cystic fibrosis gene. This means screening is never totally accurate. The tests results are only 80 to 85 percent accurate. Genetic testing has cut the birth rate of babies born with cystic fibrosis. Many prospective parents are having genetic testing and opting out of having a child if they are both carriers of the mutant gene.

The most common test to discover the presence of the mutant cystic fibrosis gene is called the sweat test. It is normally not done on an infant younger than two to three months old because they do not sweat enough to get enough samples. The sweat test measures the salt in the sweat of a patient suspected of having cystic fibrosis.

Sweat is collected from the body by first applying a substance that increase sweat on either an arm or a leg. An electrode is then placed on the area and a mild current of electricity is run through the electrode. There is not any pain associated with this test. The most you should feel is a warm feeling or a mild tingling. A special material will collect the sweat from two separate parts of the body and tested. This double test is conducted to avoid getting a false-negative or false-positive reading.

Ironically, it is normally the mother of an infant will perform her own sweat test without realizing it. She may kiss her baby and notice their skin tastes salty. Understanding this may not be normal she will take the baby to the doctor to see if there is something wrong. An infant may display signs of bowel obstructions, chronic diarrhea, bloating of the stomach, pain and excess gas. An infant that fails to grow at a normal rate even though they are eating normally should also be taken to a doctor for evaluation.

Another test used for newborns is the IRT test. Normally this test is a routine procedure done after the birth of a baby. Blood drawn two or three days after birth is analyzed for a protein called trypsinogen. If the baby’s test comes back positive, the doctor may confirm the diagnosis with a sweat test and other diagnostic tests.

Other form of testing that is done to diagnose cystic fibrosis includes chest X rays, tests to discover the lung function the patient has, and testing the sputum that a patient coughs up. There also stool examinations to make the diagnosis of cystic fibrosis.