How is it used?
CF gene mutation testing can be done to screen the general population or to screen a targeted (higher risk) subset of the population for
carrier status. It can be used to confirm the diagnosis of
cystic fibrosis (CF) in a symptomatic patient with an elevated
immunoreactive trypsinogen (IRT) or positive
sweat chloride test.
The test can be used as part of a prenatal workup, to establish carrier status in prospective parents and therefore to determine the risk CF in their infant. This may be done by sequential testing or couple testing. In a sequential strategy, the mother is usually tested first. If she is not a carrier, then any child she had would, at most, be a carrier from the father’s side. Using this logic, the father is not tested. If she is a carrier, then the father is also tested for carrier status. With couple testing, both parents are tested at the same time. In either case, follow-up genetic counseling is essential to provide couples with information on what it means to be a carrier and to explain the limitations of the testing, including the residual risk of being a carrier even if the test results were negative (e.g., there is still a slight risk that rare mutations, not included in the standard panel, might be present).
CF gene mutation testing can also be used for prenatal diagnosis if both parents are known to be carriers and if their gene mutations have been previously identified. DNA from amniocentesis and chorionic villus sampling procedures, although somewhat invasive, can be used to test the fetus for the known parental mutations.
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When is it ordered?
A doctor may order CF gene mutation testing to rule out CF when a patient has symptoms such as salty sweat, persistent respiratory infections, wheezing, persistent diarrhea, foul-smelling bulky greasy stools,
malnutrition, vitamin deficiency, or male infertility.
CF gene mutation testing may be ordered to confirm a CF diagnosis following a positive sweat chloride or IRT test. It may also be ordered as a targeted general population screen, as part of a genetic counseling workup prior to conceiving, or as an “at risk” screen, if, for example, the patient has a close relative who has been diagnosed with CF.
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What does the test result mean?
Diagnostic test results If the CF gene mutation test is positive - it comes back with two identified gene
mutations - then the patient has
CF. The test, however, cannot predict how severe or mild the symptoms may be. Patients with the exact same mutations may have very different outcomes.
If the CF gene mutation panel test reveals a single mutation or is negative and the patient is symptomatic, further mutation testing, a sweat chloride test, and/or other laboratory testing to check organ function are warranted. The patient may have a more rare form of CF that has not been identified or may have a lung or pancreatic disease or condition other than cystic fibrosis.
Carrier test results
If the CF gene mutation test comes back with a single identified mutation and the patient is asymptomatic, then chances are that the person is a CF carrier. This may be information some individuals want to know before having children. If you are identified as a carrier, your siblings may also want to verify their carrier status.
If the test comes back negative for mutations and the patient is asymptomatic, chances are that the patient does not have CF and is not a carrier. There is still a slight risk that the person could be a carrier of a rare mutation not identified with the standard panel.
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Is there anything else I should know?
Early detection of CF allows patients to be referred to CF centers for specialized care, individualized treatment plans, and careful monitoring. Beginning treatments such as taking oral enzyme supplements and fat-soluble vitamins, learning how to clear mucus out of airways, and learning to recognize respiratory infections can improve a patient’s quality of life and minimize CF complications.
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