Cystic fibrosis (CF) genotyping; CF DNA analysis; CF gene mutation panel; molecular genetic testing
To detect cystic fibrosis (CF) genetic mutations, to establish CF carrier status or to establish the diagnosis of CF in an individual
When a newborn infant has meconium ileus (no stools in the first 24 to 48 hours of life) or when a person has symptoms of CF; if a person has a positive sweat chloride or IRT test or a close relative who has been diagnosed with CF; when a patient is undergoing genetic counselling and wants to find out if they are a CF carrier with or without a family history; or for prenatal diagnosis when both partners have been identified as CF carriers
A blood sample drawn from an infant's heel; a spot of blood that is put onto filter paper; a blood sample drawn from a vein in the arm; or saliva collected via a mouthwash sample
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 chromosome 7 gene have been identified, but only a few of the mutations are common. The majority of CF in Australia is caused by a mutation called delta F508.
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 individual is suspected of having the disease.
A blood sample is drawn from an infant's heel, a spot of blood is put onto filter paper, a blood sample is obtained by inserting a needle into a vein in the arm or saliva is collected via a mouthwash sample.
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.
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.
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 panel.
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.
Early detection of cystic fibrosis 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 recognise respiratory infections can improve a patient's quality of life and minimise CF complications.
Sweat chloride, immunoreactive trypsin (IRT)
Conditions: Cystic fibrosis
Feature article: Genetic testing
Cystic Fibrosis in Australia
Cystic Fibrosis Trust
Last Review Date: March 28, 2013