What is being tested?
The CF gene mutation test identifies mutations in the CFTR gene. Each cell in the human body (except sperm and eggs) has 46 chromosomes (23 inherited from the mother and 23 from the father). Genes on these chromosomes form the body's blueprint for producing proteins that control body functions. Cystic fibrosis is caused by a mutation in a pair of genes located on chromosomes 7. Both copies (alleles) of this gene must be abnormal to cause CF. If only one copy of the gene pair is mutated, the patient will be a carrier. Carriers are not ill, they do not have any symptoms, but they can pass their abnormal CF gene copy on to their children.
To date, almost 2,000 different mutations of the CFTR gene have been identified, but only a few of the mutations are regularly seen. The majority of CF in Australia is caused by a mutation called F508del (previously known as deltaF508).
When CF gene mutation testing is done, the laboratory specifically examines the CFTR gene on each chromosome 7 for a number of mutations. If the initial panel of mutations demonstrates a mutation, additional testing for other mutations may be indicated if the person is suspected of having cystic fibrosis.
How is it used?
CF gene mutation testing can be used to confirm the diagnosis of CF in a symptomatic patient with an elevated IRT or sweat chloride test. It can also be used to clarify CF carrier status for individuals with or without a family history.
When is it requested?
A doctor may use CF gene mutation testing to rule out CF if the patient has symptoms such as salty sweat, persistent respiratory infections, wheezing, persistent diarrhoea, foul-smelling bulky greasy stools, malnutrition and vitamin deficiency.
CF gene mutation testing may also be used to confirm a CF diagnosis following a positive sweat chloride or IRT test. CF gene mutation testing may also be used to determine CF carrier status.
What does the result mean?
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 tell how severe or mild the symptoms may be. Patients with the exact same mutations may have very different outcomes.
If the test comes back negative for mutations and the patient is asymptomatic, chances are that they do not have CF and are not a carrier. There is still a slight risk that the person could be a carrier of a rare mutation not picked up with the standard testing.
If the CF gene mutation test is negative and the patient is symptomatic, the doctor may recommend further genetic testing, a sweat chloride test, and other laboratory testing to check organ function. The patient may have a more rare form of CF that is not being identified or may have a lung or pancreatic disease or condition other than cystic fibrosis.
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.
Is there anything else I should know?
Early detection of cystic fibrosis is important. It enables people to be referred to specialist care and begin treatments such as taking oral enzyme supplements and fat-soluble vitamins. Also, by learning how to clear mucus out of airways and learning to recognise respiratory infections a person's quality of life can be improved and CF complications minimised.
Common questions
No, it is only checking for specific CF mutations. Each genetic condition requires specific DNA testing to identify it (assuming that the gene and mutations causing it are known - that is the first step).
Since the ethnicity of the Australian population is becoming increasingly blended, the historical data and statistical risks are changing. Your risk will be an unknown mix of your inherited ethnic risk. Some families may also carry the additional risk of specific rare mutations within their family line.
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