Cystic fibrosis (CF) is a genetic disorder that affects mainly the lungs and digestive system causing the glands to produce abnormally thick mucus. In the lungs, this mucus causes obstruction in the air passage, leading to frequent and severe infections. In the digestive system, normal digestive enzymes are obstructed leading to poor absorption of food and pancreatic damage leading to diabetes.

Cystic fibrosis is caused by alterations (called mutations) in the CFTR gene. Individuals within the general population can be:

• Normal: These individuals have two normal copies of the CFTR gene (Figure 1a) and are unaffected and not at risk of passing this disease on to their children
• Carrier: These individuals have one normal copy and one altered copy of the CFTR gene (Figure 1b). Carriers are unaffected but will pass on an altered copy to half their children. When two carriers have children together, an average one in four of their children will have CF.
• Affected: These individuals have two altered copies of the CFTR gene (Figure 1c) and are affected with CF. All their children will be carriers (and probably quite well) but should their partner be a CFTR carrier, half their children will have this disease.

Figure 1 (above): Cystic Fibrosis genetic status. The red X's indicate Cystic Fibrosis mutations.

Why screen for Cystic Fibrosis?

Cystic fibrosis is one of the most common genetic diseases in the population, affecting 1 in 2500 newborn children. Approximately 1 in 25 people in the population carries an altered copy of the CFTR gene and most have no family history of cystic fibrosis.

At Monash IVF, sperm and egg donors are routinely screened for alterations in the CFTR gene. By identifying the CF status of the donor, it is possible to determine whether a particular recipient couple are at risk of having a child with CF.

Knowledge of your CF status will also be of value to you for family planning decisions. For example, if you are a carrier of CF, it would be advisable to have your partner tested to determine their CF status prior to natural conception.

What does CF testing involve?

A blood sample is taken and sent to the Victorian Clinical Genetic Service at the Murdoch Children's Research Institute in Melbourne for analysis.

There are over 800 recognised mutations in the CFTR gene. The test screens for the twelve most common CFTR gene changes found in the Australian population. These twelve mutations are responsible for approximately 80% of all CF cases. Therefore, if you carry a CF mutation, there is an 80% chance that it will be detected using this test.
You will be notified if a mutation in the cystic fibrosis gene is detected and offered an appointment with a clinical geneticist to discuss the result.