Definition
Medical (clinical) genetic testing is often performed as part of a genetic consultation and is usually ordered through a doctor or genetic specialist. Testing involves the analysis of a person's DNA, RNA, chromosomes, genes, proteins, or certain metabolites that are obtained from a sample of blood, hair, skin or other tissue (such as cheek cells). Newborn screening (which will be discussed separately due to its uniqueness) involves the analysis of a small blood sample pricked from a baby's heel.
Different methods of testing can be used to obtain a genetic diagnosis. For more information see Genetic Testing Methods.
Before testing, it is always important to fully understand the potential risks, benefits, limitations, and consequences of the test and its results. The process of educating a person about the test and obtaining permission for testing is called informed consent.
In general, the results of a medical genetic test can confirm or rule out a suspected genetic condition; aid in the prediction, prevention or treatment of a condition; or help determine the chance to pass down a genetic condition. To make it easy, we divided clinical genetic testing into some common categories below.
Diagnostic Testing
Diagnostic testing is used to identify or rule out a specific genetic or chromosomal condition. In many cases, genetic testing is used to confirm a diagnosis when a particular condition is suspected based on physical signs and symptoms.
- Diagnostic test results can impact a person's choices about health care and management of a disorder.
- Diagnostic testing may have implications for family planning and children.
- Diagnostic testing may have implications for other family members.
- Diagnostic testing may have psychosocial implications.
- Diagnostic testing (by DNA analysis) may or not be the best way to diagnosis a medical condition and multiple tests (genetic and non-genetic) may be needed to establish a diagnosis.
- Diagnostic testing is typically only available through an in person genetic consultation involving a medical geneticist and/or genetic counselor.
Carrier Testing
Carrier testing is used to identify people who carry one copy of a gene mutation that, when present in two copies, causes a genetic disorder.
- Carrier testing can be used for genetic conditions with either autosomal recessive inheritance or X-linked recessive inheritance. In autosomal recessive and X-linked recessive conditions, it is necessary to have two mutations, one in each gene copy, to be affected. When only one mutation is present, the person is considered to be a carrier of the disease. Carriers usually do not have any symptoms of the disease with the exception of certain disorders where they may have mild symptoms.
- Carrier testing is often performed on people who have a family history of a genetic condition and/or symptoms of a genetic condition, or on people in certain ethnic groups who have an increased risk for specific genetic conditions.
- Carrier test results can provide information about a couple's risk of having a child with a genetic condition. These results can be used for prenatal testing purposes.
- Carrier testing may have implications for other family members.
- Carrier testing may have psychosocial implications.
- Carrier testing is available online (over the internet) for limited number of genetic conditions.
- Carrier testing is also available through an in person genetic consultation with a medical geneticist and/or genetic counselor.
Prenatal Testing
Prenatal testing is used to identify or rule out a suspected genetic condition in a fetus before birth. Prenatal testing usually involves the analysis of fetal skin cells in amniotic fluid (via an amniocentesis) or placental cells (via a CVS).
- Prenatal testing typically involves a procedure such as CVS, amniocentesis, and less commonly percutaneous umbilical cord sampling (PUBS); the risks, benefits, and limitations of which should be discussed and understood beforehand.
- Prenatal testing is typically offered when a couple is at increased risk to have a child with an genetic or chromosomal disorder. One common example of a chromosomal disorder is Down syndrome.
- Prenatal test results can impact a couple's decision about whether or not to continue a pregnancy.
- Prenatal testing may have implications for future family planning and children.
- Prenatal testing may have implications for other family members.
- Prenatal testing may have psychosocial implications.
- Prenatal testing (via DNA analysis) may or not be the best way to diagnosis a medical condition and multiple tests (genetic and non-genetic) may be needed to establish a diagnosis.
- Prenatal testing is typically only available through an in person genetic consultation involving a medical geneticist and/or genetic counselor.
Predictive Testing
Predictive (also known as presymptomatic) testing is used to detect gene mutations associated with genetic disorders that appear after birth, often later in life. These tests can be helpful to people who have a family member with a genetic disorder, but who have no features of the disorder themselves at the time of testing.
- Predictive testing sometimes involves specific testing protocols due to potential impact of test results and significant psychosocial implications.
- The results of a predictive test can impact a person's choices about health care, management of a disorder, family, work, finances, lifestyle, as well as environment. Examples of conditions that may have predictive testing include Huntington's disease and early-onset Alzheimer's disease.
- Predictive testing may have implications for family planning and children.
- Predictive testing may have implications for other family members.
- Predictive testing (via DNA analysis) may or not be the best way to diagnosis a medical condition and multiple tests (genetic and non-genetic) may be needed to establish a diagnosis.
- Predictive testing is typically only available through an in person genetic consultation involving a medical geneticist and/or genetic counselor.
Susceptibility Testing
Susceptibility testing is used to detect gene mutations associated with an increased risk to develop a multifactorial condition. Multifactorial conditions are caused by a combination of genetic, lifestyle and environment factors.
- The results of a susceptibility test can impact a person's choices about health care, management or treatment of a disorder, family, work, finances, lifestyle, as well as environment.
- Susceptibility testing is not available for all multifactorial conditions.
- Susceptibility testing may have implications for family planning and children.
- Susceptibility testing may have implications for other family members.
- Susceptibility testing may have significant psychosocial implications.
- Susceptibility testing (via DNA analysis) may or not be the best way to assess risk for a condition and multiple tests (genetic and non-genetic) may be needed to better quantify risks.
- Susceptibility testing is available online (over the internet) for limited number of multifactorial conditions.
- Susceptibility testing is also available through an in person genetic consultation with a medical geneticist and/or genetic counselor.
Cancer Predisposition Testing
Cancer predisposition testing is used to detect gene mutations associated with an increased risk to develop cancer.
- Cancer predisposition testing sometimes involves specific testing protocols due to potential impact of test results and significant psychosocial implications.
- The results of a cancer predisposition test can impact a person's choices about health care, management of a disorder, family, work, finances, lifestyle, as well as environment.
- Cancer predisposition testing is not available for all cancers.
- Cancer predisposition testing may have implications for family planning and children.
- Cancer predisposition testing may have implications for other family members.
- Cancer predisposition testing (via DNA analysis) may or not be the best way to diagnosis a medical condition and multiple tests (genetic and non-genetic) may be needed to establish a diagnosis.
- Cancer predisposition testing is available through an in person genetic consultation involving a medical geneticist and/or genetic counselor.
- Cancer predisposition testing is available online (over the internet) for limited number of cancers.
Preimplantation Genetic Diagnosis (PGD)
Preimplantation genetic diagnosis (PGD) also called preimplantation testing is used to detect genetic changes in embryos that were created using assisted reproductive techniques such as in-vitro fertilization. In-vitro fertilization involves removing egg cells from a woman's ovaries and fertilizing them with sperm cells outside the body. To perform preimplantation testing, a small number of cells are taken from these embryos and tested for certain genetic changes.
- PGD can reduce the risk of having a child with a particular genetic or chromosomal disorder but does not completely eliminate it.
- PGD can impact a couple's decision about which embryos to implant.
- PGD may have implications for family planning and children.
- PGD may have implications for other family members.
- PGD (via DNA analysis) may or not be the best way to diagnosis a medical condition and multiple tests (genetic and non-genetic) may be needed to establish a diagnosis.
- PGD is typically only available through an in person genetic consultation involving a medical geneticist and/or genetic counselor.