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Cystic Fibrosis

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What is Cystic Fibrosis?
Cystic Fibrosis (CF) is an inherited (genetic) disorder which affects the mucus producing glands of the body, as well as the sweat glands. People who have CF produce a mucus which is thick and sticky because it contains the wrong amount of salt and water. This mucus interferes with the lungs and digestive system. Everyone normally produces a protein which is involved in removing salt from the cells, however, people with CF lack the genetic information to tell the body to produce the correct protein and therefore they produce a protein whose function is impaired and thus the salt is not removed. It builds up in the cells and the resulting sticky mucus clogs the small air passages in the lungs, bacteria are trapped and repeated infections and blockages can cause severe lung damage. Incomplete digestion, due to blockage of the ducts that connect the pancreas to the intestine, results in weight loss in spite of a hearty appetite.

The severity of the disease depends on the type of fault (mutation) affecting the gene as well as environmental factors. Those affected have a varied life expectancy. Some do not survive past their teen years and others lead a relatively active life till 40 or even 50 years of age.

Who gets Cystic Fibrosis?
Genetic diseases are often more common in specific community groups. Cystic Fibrosis is found primarily in the Caucasian population.

What causes Cystic Fibrosis ?
CF is caused by inheriting a 'double-dose' of a fault in a gene (called the CFTR gene) which codes for the cystic fibrosis transmembrane regulator protein. Every person has two copies of each gene. A person will only be affected by CF if s/he has a fault in both copies of the CFTR gene. This can only happen if one faulty copy is inherited from each parent. One in every 25 Caucasians carries one copy of the faulty gene and one regular copy of the gene. CF does exist in other communities, but at a lower frequency. Carriers themselves are not affected by the disease.

How is the disease transmitted?
When two healthy carriers of the CFTR gene mutation become parents, then for each pregnancy:
cf
  • There is a 1-in-4 (25%) chance that the child will inherit the regular CF gene from each parent and will be completely free of the CF gene mutation and will not be affected by CF (figure A).
  • There is a 2-in-4 (50%) chance that the child will inherit both a regular copy and a faulty copy of the CF gene and be a carrier of the faulty gene, unaffected by CF, just like his/her parents (figures B and C).
  • There is a 1-in-4 (25%) chance that the child will inherit the faulty CF gene from each parent. This child will be affected with cystic fibrosis (figure D).



Does it affect one's health to be a carrier of the CF genetic mutation?
No. Carriers of the CFTR gene mutation are completely unaffected by CF.

Does Cystic Fibrosis affect only males?
No. Cystic Fibrosis can affect both males and females.

Why is a person's ancestry relevant to genetics carrier testing?
There are different types of faults (mutations) found in genes. Some faults are specific to particular ethnic groups or regions of the world.

For whom is genetics carrier testing for Cystic Fibrosis relevant?
Testing is available for all men and women over the age of 16. However, it is particularly relevant for Caucasians.

How is the testing performed?
A small blood or mouth wash sample is taken and the most common mutations which cause CF are tested for.

What do the test results mean?
There have been over 800 mutations in the CFTR gene found to date, which makes the gene faulty. Some of these are more common than others and in fact, some are extremely rare. The current laboratory tests are designed to detect the most frequently occurring mutations found in the Australian population. In about 85% of the Australian population who have a faulty CFTR gene, these tests will detect its presence. But in 15% of the population who have faulty CFTR gene, with routine screening the fault cannot be found.

This means that if the laboratory test shows that a person has a fault in one copy of their CFTR gene then that person is definitely a genetic carrier of CF.

On the other hand, if the laboratory test does not detect the presence of a fault in the CFTR gene, there is a greater than 99% chance that this person is not a genetic carrier of CF. Of course, there still remains a very small chance that this person is carrying a rare fault in their CFTR gene which would make them a genetic carrier of CF.

Is there a cure?
At this stage there is no cure for CF. However, treatment helps people with CF to grow and develop as near to normal as possible, but they frequently need hospitalisation.

What confidence can I have in the test results?
The accuracy of the results will depend on your ancestry. Some mutations are specific to certain regions of the world or certain ethnic groups. The various laboratory tests being used have each been designed to detect specific genetic faults and are most accurate when testing individuals who are of particular ancestries and origins. Our staff will need to find out about your ancestry. Any mutation in the CFTR gene will be reconfirmed by a second method.

If I do not have a family history of Cystic Fibrosis do I need to be tested?
Yes. Over 95% of the couples with children affected by CF have no family history of the disease because the faulty CFTR gene is silently passed down through the generations. However, if you do have a family history, then the risk is much greater. People who have a known family history of cystic fibrosis should seek further information though genetics counselling (telephone: (61) 2 9926 7324).

Is genetics carrier testing available for other conditions?
Yes. The laboratory can test for genetic carriers of some other inherited disorders at the same time as testing for CF. Testing is already available for Tay-Sachs disease, another genetic condition inherited in a similar manner to CF. Over the next few years, testing will become available for other inherited conditions. You will be asked to provide written consent if you want us to test for these additional conditions in the future.

moreinfo link Contact: PaLMS Laboratory & Community Genetics: Ph:992-68899 Fax:9926-8484 Email:aproos@doh.health.nsw.gov.au

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