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What is cystic fibrosis?
Cystic fibrosis (CF) is an inherited disease that affects the lungs, digestive system, sweat glands and male fertility. Despite advances in treatment, CF remains incurable. Repeated infections and blockages from the excess mucus produced by cystic fibrosis can cause irreversible lung damage and an early death.
How common is cystic fibrosis?
Cystic fibrosis affects 1 in every 2,500 Australian babies born. It is estimated that 1 in every 25 Caucasian Australians are carriers. Carriers exhibit no symptoms of the disease. Faulty CF genes are also found in people from other ethnic groups, but the frequency is less. For example, only 1 in 90 Asian people are carriers. Individuals with a family history of CF have a higher chance of being a carrier, but over 85% of children born with CF do not have a known family history of the disease. On average a CF baby is born every four days in Australia. CF is the most common life threatening recessive genetic condition affecting Australian children. 1 in 25 Caucasian Australians are carriers.
How is cystic fibrosis transmitted?
Cystic fibrosis only occurs in the child of two parents who both carry a mutation in the CF gene. When two carriers have a child, there is a 1 in 4 chance (25%) their child will be a CF sufferer, a 1 in 2 chance (50%) that their child will be a carrier, and a 1 in 4 chance the child will have two normal genes. It follows that just because a couple have had one or more non-CF children, it does not mean that they are not carriers and that future children will not be affected.
Should I be screened?
Genetic testing for cystic fibrosis (CF) looks for the most common genetic changes (mutations) in the gene that causes CF. People typically want CF carrier screening for family planning purposes. Genea has two types of screening tests:
- Standard (F508del only) - The standard test screens for the “F508del” gene which accounts for the majority of Caucasian CF cases. Often people choose this test to test both parents to detect carrier status. Testing an individual will detect 70% of carriers. Testing both parents increases the detection to 90% of at risk couples.
- Comprehensive - (Cystic Fibrosis 32-Mutation Multiplex Screen) The comprehensive test screens for the 32 most common CF mutations, which detects about 90% of Caucasian CF mutations in individuals. It detects slightly less than 90% of the mutations in people with ethnic backgrounds. Non-Caucasians and people with a family history of CF often choose this test.
Why you might not want to be screened
The risk for having a mutation in the gene for CF depends on your ethnic background. Your ethnic background -see table -may put you in a low-risk category. Or you may have other reasons for not wanting screening such as cost or religious beliefs. The risk for having a mutation in the gene for CF depends on your ethnic background (for persons without a family history of CF) In the absence of a family history of CF the likelihood of an undetected mutation nevertheless being present is less than 1% (extremely unlikely but, like most tests, is not an absolute zero).
If you have questions regarding this test, please contact our genetic counsellor for more information on 1800 689 908. As the tests are not Medicare rebatable you can order the test without a doctor’s referral. You are encouraged, though, to communicate the results of the test with your health professional and family members.
Options for known carriers
If both parents are screened and no mutation is identified in either, the risk of a child affected by CF is small but never zero because we cannot test for all CF mutations. If both parents are screened and both are identified as carrying a mutation, the risk of having a child affected by CF is 1 chance in 4. Carriers have several options:
- Genea provides preimplantation genetic diagnosis(PGD) for CF carrier couples, where unaffected IVF embryos can be specifically selected for transfer.
- Have a natural pregnancy and have the baby tested at around 11 weeks in the pregnancy. If the baby is found to have CF, termination of the pregnancy is an option.
- Have an unassisted pregnancy and prepare for 25% chance of conceiving a child with CF.