genetic testing and screening

test overview

a genetic test checks the dna of your cells. it can find changes in your genes or chromosomes that may cause a genetic illness. the results may tell you about your ancestry, your health, or your risk for certain diseases.

testing can be done on a single gene, selected genes, or all of your genes (your genome). the test can look for a single change in a gene or check the entire gene or chromosome for changes.

genetic screening tests include prenatal screening and carrier screening. prenatal screening checks a fetus for possible genetic problems. carrier screening shows if an adult carries a gene change that could be passed along to their child.

you inherit half of your genetics from each birth parent. genes determine things like your blood type, hair colour, and eye colour. genes can also affect your response to medicines.

what are the main types of genetic testing?

genetic tests include:

• carrier testing. this looks for gene changes that a person might pass along to their child.
• prenatal screening and testing. this checks if a fetus is at risk for or has a condition like down syndrome.
• predictive testing. this is done to see if a person has a genetic change that increases their risk for developing a disease such as huntington disease.
• forensic testing. this is used to identify family members, crime suspects, and victims of crime, war, or disasters.
• diagnostic testing. this may be used to confirm a specific genetic illness when a person has symptoms of a disease.
• pharmacogenomic testing. this is done to see if a person has gene changes that might affect how their body reacts to a specific medicine.
• at-home genetic testing. this may offer information on ancestry, personal traits, lifestyle factors, and disease risks.

how can genetic counselling help?

the results of genetic testing can affect your life. genetic counsellors are trained to help you understand your risk of getting genetic diseases or having a child with an inherited disease, such as cystic fibrosis. it may be a good idea to get genetic counselling before deciding to have testing.

genetic counselling may involve:

• discussing what problems an inherited disease may cause.
• teaching you and your partner about how a specific disease is inherited or passed from you to your child.
• discussing whether and how to test for an inherited disease before you become pregnant or before your child is born.
• discussing the likelihood that you and your partner will have a child with an inherited disease, based on test results.

medical geneticists and genetic counsellors are trained to help you and your family make informed decisions that are right for you. they are sensitive to physical and emotional aspects of these decisions. your privacy and confidentiality are carefully protected.

why it is done

testing may be done to:

• find out if you carry a gene for an inherited disease, such as cystic fibrosis.
• find out if your fetus is at risk for a genetic condition such as down syndrome.
• find out if you carry a gene that increases your risk for a disease later in life, such as breast cancer.
• find out if you have an inherited heart disease called hypertrophic cardiomyopathy.
• check for genetic changes that may affect your treatment for an existing disease.
• find out if you have inherited gene changes that affect your response to medicines.
• identify family members, crime suspects, or victims of war or disasters for legal purposes.

how to prepare

you do not need to do anything special to prepare for most of these tests. your doctor will tell you how to prepare if you are having an amniocentesis or chorionic villus sampling.

talk with your doctor if you have any concerns about the need for the test, its risks, how it will be done, or what the results will mean.

the information found by a genetic test can have a big impact on your life. so before you have the test, you may want to talk to a genetic counsellor or a doctor who specializes in genetics (geneticist). genetic counselling can help you understand your genetic risks and decide if you want testing.

how it is done

genetic testing for inherited gene changes can be done using almost any cell or tissue from the body. the type of sample needed will depend on the test.

samples used in tests include:

• a blood sample from a vein. a health professional uses a needle to take a blood sample, usually from the arm.
• a cell sample from the cheek. a swab is used to scrape some tissue from the inside of the cheek.
• a saliva sample. the person being tested spits into a tube.
• a sample of amniotic fluid. this is collected using amniocentesis or chorionic villus sampling.

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how it feels

depending on the test, a sample of blood, saliva, amniotic fluid, or other tissue may be used.

• a blood sample from a vein may involve a quick sting or pinch from the needle.
• a saliva sample can be collected by having you spit into a tube. it isn't painful.
• a cheek swab collects cells from the inside lining of your cheek. it isn't painful.
• a sample of amniotic fluid is removed from your uterus (amniocentesis). you may feel a sharp sting for a few seconds when the needle is put in. as the fluid is taken out, you may feel some pulling or pressure in your belly. after the test, the area may be tender or sore for a few days.

risks

risks from gathering a sample

there is a very low risk of problems from taking samples of blood, saliva, or cells from a cheek swab. there are some risks with having a chorionic villus sampling (cvs) or an amniocentesis, including a small chance that the test may cause you to have a miscarriage.

other risks

the information from a genetic test for inherited gene changes can affect you and your family in many ways. for example, it may affect:

• your emotions and relationships. it may be difficult to learn that you are likely to have a serious disease or have a child who has a disease. this news may also affect your relationship with your partner or other family members.
• your treatment choices. if you test positive for a disease-specific gene change, you may have preventive or treatment options to reduce the impact or severity of the disease.
• your pregnancy decisions. genetic testing can help you make decisions about your pregnancy or plan for the future. if you find out that your fetus has a genetic disease, you may decide to end the pregnancy. or you may change your delivery plans. if your baby is likely to need special care after birth, you may need to deliver in a hospital that can provide this care.
• your privacy. many people worry that test results could affect their future employment options or the cost or availability of private insurance. in canada, there is a law called the genetic non-discrimination act (gna). it protects your genetic information.

results

the results of genetic testing depend on the type of test done. for example, the results may show if you have a genetic condition, how likely it is that you will have a genetic condition in the future, or if you are a carrier for a condition. the results of prenatal genetic screening may show how likely it is that your fetus will have a genetic condition or birth defect.