May 2010
Written by Sigrid Auweter

How does it work?
Today, it is possible to isolate DNA from the tiniest bits of biological sample, like a drop of blood, a single hair, or a flake of skin. The DNA can then be amplified, visualized on gels and sequenced. These technologies have made it possible to detect and diagnose many genetic conditions in adults and unborn children.

Some genetic disorders are also tracked down by looking directly at a patient’s cells and don’t need the amplification techniques. Down syndrome is a condition where one of the chromosomes, chromosome 21, appears three times, instead of twice. The extra chromosome can be seen when looking at the patient’s cells through a microscope.

Genetic testing does not always mean analyzing DNA. Sometimes it is easier to look at the resulting effects. For example, people with the disease phenylketonuria (PKU) have a mutation in the gene that is necessary to degrade the amino acid phenylalanine. These patients have a higher than average amount of phenylalanine and PKU is detected by measuring blood phenylalanine levels.

What is it good for?
There are many different uses for genetic testing. For example, you may be healthy yourself, but you know that there is a recessive genetic disorder running in your family. So before you decide to have a baby, you want to know if you are a carrier for this disease to find out if the baby can be affected.

Another use of genetic testing is newborn screening. Most babies in Canada are screened for a whole bunch of treatable genetic diseases, such as PKU, within the first few days of life.

A major application of genetic tests is identity testing. This is used in forensics to find out whether or not a suspect has been at a crime scene. Likewise, the same technology can also be used for paternity testing.

What are some concerns about using genetic testing?
The uses of genetic testing mentioned so far are quite standard and mostly accepted.  As you may know, though, some other types of genetic testing have caused a bit more controversy because they raise certain ethical concerns.

For example, if you know that there have been cases of an adult-onset disorder such as Huntington’s disease in your mother’s side of the family, you can get tested to find out whether you will develop the condition later in life. It is a very personal decision if this is something you want to know about or not. However, imagine you want to find out, but your mother does not want to know. If you are tested positive, your mother will know for sure that she has the gene and will develop Huntington’s at some point in her life.

It is also fairly common today to test unborn children for genetic conditions. Pregnant women are offered prenatal genetic tests to detect chromosome disorders like Down syndrome and trisomy 18 or single gene disorders like alpha thalassemia.

Perhaps the most controversial use for genetic testing is preimplantation genetic diagnosis. If couples have difficulty getting pregnant naturally, they can choose to get in vitro fertilization. Because fertilization happens outside the body, it is possible to check the embryo for mutations or incorrect number of chromosomes.  Implanting healthy embryos increases the chance that the pregnancy will be successful. One concern is that parents will start to select for more than general health and screen for things like eye color and musical talent.

To learn more about the different types of genetic testing, click on the links below:

• To learn more about genetic testing for adult-onset disorders and its pros and cons, click here
• To learn more about prenatal genetic testing offered to pregnant women in Canada, click here
• To learn more about preimplantation genetic diagnosis, click here