CF Gene Mutation Testing
When a newborn baby has no stools in the first 24 to 48 hours of life (meconium ileus) or when a person has symptoms of CF; if a person has a positive sweat chloride or an immunoreactive trypsin test or a close relative who has been diagnosed with CF; or when a patient is undergoing genetic counselling and wants to find out if they are a CF carrier. In addition, high risk carrier couples may have the test prior to in vitro fertilization so that the test can be carried out before implantation.
A blood sample taken from an infant's heel; a spot of blood that is put onto filter paper; or a blood sample taken from a vein in the arm
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.
So far, over 1500 different mutations of the chromosome 7 gene have been identified, but only a few of the mutations are common. The majority of CF in the UK is caused by a mutation called 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 done if the individual is suspected of having the disease.
How is the sample collected for testing?
A blood sample is taken from an infant's heel, a spot of blood is put onto filter paper, or a blood sample is obtained by inserting a needle into a vein in the arm.
Is any test preparation needed to ensure the quality of the sample?
No test preparation is needed.
How is it used?
When is it requested?
A doctor may use CF gene mutation testing to rule out a diagnosis of CF if the patient has symptoms such as salty sweat, continuous lung 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.
What does the test 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 does not have symptoms, it is likely 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 tests.
If the CF gene mutation test is negative and the patient has symptoms, 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 does not have symptoms, then the 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, then brothers or sisters may also want to check their carrier status.
Is there anything else I should know?
Early detection of CF allows patients to be referred to specialist care. 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.
Will this CF gene mutation test pick up any other genetic diseases?
What will my risk of being a carrier be if I am of mixed ethnicity?
Since the ethnicity of the UK 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.