Genetic testing involves checking genes and / or chromosomes for abnormalities. This is done by sampling and analyzing blood or tissue in a laboratory. Note: The following information is a general guide only. The agreements and the way tests are performed, may vary between different hospitals. Always follow the instructions of your doctor or local hospital.
On this page
- A note about DNA, genes and chromosomes
- What is genetic testing?
- Why is genetic testing?
- How is genetic testing?
- What about genetic counseling?
- Karyotype testing – this test gives a picture of all the chromosomes of a person from the largest to the smallest.
- The fluorescence in situ hybridization (FISH) analysis – this can be found small fragments of chromosomes are missing or have extra copies. These small changes may be lost by karyotype testing.
- Give a diagnosis if someone has symptoms suggestive of a genetic disease.
- Show whether a person is a carrier of a genetic disease. Carriers have an altered gene but do not have the disease. However, they can pass the altered gene to their children, who have a chance of inheriting the disease.
- To help expectant parents to see if an unborn child has a genetic condition is. This is called prenatal testing.
- Screen newborns missing or abnormal proteins that can cause disease. This is called newborn screening.
- Show whether a person has an inherited predisposition to a certain disease before symptoms appear.
- The risk of inheriting or passing a genetic disease.
- The implications of a positive result for the disease, including the psychological impact and other consequences.
- Whether to inform relatives of their intent to test or not to test.
- The usual pattern of progression of the disease being tested for and possible treatments.
A note about DNA, genes and chromosomes
Your body is made up of millions of tiny cells. The different cell types form the various structures of the body – skin, muscles, nerves, organs, etc. In the center (nucleus) of most cells in the body have 46 chromosomes arranged in 23 pairs. One of each pair comes from the mother and one from their father. Chromosomes are made of DNA. DNA stands for deoxyribonucleic acid. DNA is the genetic material.
A gene is the basic unit of genetic material. It consists of a sequence (or parts) of DNA and sits in a particular place on a chromosome. Thus, a gene is a small section of a chromosome. Each gene controls a feature or has a specific function in the body. For example, dictating your eye color or hair color, so that all the different proteins in the body, etc. Each gene is part of a couple. One of the genes of each pair is inherited from his mother, the other from their father. Each chromosome carries hundreds of genes.
Humans have 20,000 to 25,000 genes in total. The total of all genes called genome.
As our cells divide all the time, our genetic information must remain the same. Normally, there are excellent mechanisms to ensure that every cell has the same exact copy of the DNA, the material that makes up our genes. But sometimes the copying mechanism makes mistakes or other problems may occur with their genetic material. Problems and abnormalities in genes can lead to genetic diseases.
What is genetic testing?
What is genetic testing?
Genetic testing for abnormalities in DNA taken from the fluid of a person's blood or body tissues. Tests can search large errors such as a gene that has a section missing or added. O tests can find small changes in DNA. Other errors that can be found are the genes that are overactive, the genes that are turned off, or have been lost entirely.
Genetic tests examine the DNA of an individual in a variety of ways. Some tests use probes. These are short stretches of DNA that form the other half of an altered gene. DNA probes search matches this altered gene into the genome of an individual. If a gene is altered, the probe binds to the same, identifying the alteration.
Another type of test gene directly compares the DNA sequence in the gene of an individual to a normal version of the gene.
What is chromosome testing?
Chromosomal tests look at the features of a person's chromosomes, including their structure, number and arrangement. These tests can detect changes, such as pieces of chromosomes on or be in a different place.
Types of chromosomal tests include:
There are also tests that can detect low levels of protein. This may indicate that the gene which produces the protein is defective.
Why is genetic testing?
Genetic testing can be done for many different reasons, including:
How is genetic testing?
Genetic testing usually involves taking a sample of blood or tissue.
In adults and children usually this involves taking a blood sample from a vein.
In pregnancy, a sample may be taken from the baby by amniocentesis or CVS test. In amniocentesis a sample of the liquid (amniotic fluid) that surrounds a baby is born. This is done by placing a needle when the abdomen (belly) in the uterus. In testing a sample of chorionic villi of the placenta part is taken. This is done either by inserting a needle into the abdomen as amniocentesis or by placing a thin tube into the cervix (neck of the womb). Both tests involve a small risk that you will suffer a miscarriage as a result of having the test. If you are offered these examinations will discuss the risks to help you make a decision on whether to have the test.
In newborns, routine screening for diseases such as phenylketonuria occurs as part of a newborn baby checkup.
After the sample has been taken is sent to a laboratory for analysis. It may take some time for the results of all the tests to come back. Your doctor should advise how long the results.
What about genetic counseling?
The information from genetic testing can have a profound impact on your life. Genetic counseling is available for anyone undergoing or planning to undergo any form of genetic testing. Genetic counseling is a psychological therapy. It aims to provide all the information you need to make a decision on whether to undergo genetic testing.
This may include information about:
After the test is also available to help you deal with the test results.
