What is genetic carrier testing?

Genetic carrier testing is the process of analysing a person’s genetic material (DNA) to look for specific faults that may lead to disease in their future children.

How are autosomal recessive disorders transmitted?

Genes contain the information that tells our bodies how to grow, develop and work. Genes are passed from parents to children. We all have two copies of each gene in the cells of our bodies, one copy from each parent. Many illnesses are caused by inheriting faults in both copies of particular genes. These are known as autosomal recessive disorders.

People who have a fault in only one copy of these particular genes do not have the disease since they have a regular copy that can provide all the necessary information to the cells. They are called a “carrier” of the faulty gene. When both parents are carriers of the same faulty gene, there is a 1 in 4 chance that their children may inherit the faulty copy from both parents and thus be affected by the genetic disorder. This is called autosomal recessive inheritance.

Figure 1

Figure 2

A baby receives one copy of each gene from each parent, thus being a “mixture” of genetic information from his/her parents, see figure 1 and 2.

  • Figure 1: When two unaffected carriers of the gene mutation become parents,  for each pregnancy:
    • There is a 1 in 4 (25%) chance that the child will inherit the regular gene copy from both parents and will be completely free of the gene fault and will not be affected by the disorder or be a carrier of the faulty gene (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 gene. The child will be a carrier of the faulty gene, UNAFFECTED by the disorder, just like his/her parents (figures B and C).
    • There is a 1 in 4 (25%) chance that the child will inherit the faulty gene from both parents. This child WILL BE AFFECTED by the disorder (figure D).
  • Figure 2 shows that if only one parent is a carrier, there is no chance that they will have a baby affected with the disorder, however, there is a 50% chance that each of their children will be carriers of the faulty gene.

Does it affect one’s health to be a carrier of a genetic mutation?

No. Carriers of a faulty gene copy are completely unaffected by the disorder.

Does an autosomal recessive disorder affect only males?

No. These disorders can affect both males and females.

Is it possible to test to see if a person is a carrier of the faulty gene?

Yes. For most genetic disorders the gene and gene faults (mutations) have been identified enabling the testing laboratory to look for a set panel of mutations.

Why is a person’s ancestry relevant to genetic carrier testing?

There are different faults (mutations) found in genes. Some faults are specific to particular ethnic groups or regions in the world. Laboratory tests are commonly designed to detect specific genetic faults that are most prevalent among individuals who are of particular ancestries.

For whom is genetic carrier testing for these disorders relevant?

Testing is available for all men and women over the age of 16. It is particularly relevant for those with Ashkenazi Jewish ancestry and individuals with a history of a genetic disorder in their family.

People who have a known family history of a disorder should seek further information through your local genetic counselling service (listed at www.genetics.edu.au).

If I do not have a family history of the disease do I still need to be tested?

Yes. Over 95% of the couples with children affected by a disease have no family history of the disease because the gene is silently passed down through the generations.

What confidence can I have in the test results?

The testing laboratory has been fully accredited for medical testing by the NATA/RCPA accreditation program, and is certified to the international medical laboratory standard ISO 15189, as well as to the quality management standard ISO 9001.

The sensitivity of the results will depend on your ancestry, as some mutations are more common in individuals of particular origin. Any gene mutation detected is confirmed by a second method.

Limitations of genetic testing

Testing through these programs is designed to look for specific genetic changes only. There are other, less common, changes in the same genes which are not detected by these tests. This means that a normal result does not rule out the possibility that the tested person is a carrier, it just makes it less likely.