You have probably seen advertising for genetic or DNA tests on television or online. Many of these tests enable you to trace your ancestry back hundreds of years, a project some people find to be interesting and rewarding. Other types of tests offer the promise of learning more about your health. Certain types of testing do have real, practical uses in health care – but not all the time, and not for all people.
DNA, Genes & Chromosomes
When thinking about genetic testing, it is helpful to first do a quick review of high school biology class, or at least the part when we learned about DNA, genes and chromosomes.
Deoxyribonucleic acid (DNA) is the material present in all living entities on earth that provides the genetic instructions for each being. DNA looks like a twisting ladder – a double helix – and contains four different bases. The order or sequence of these four bases determines genetic makeup.
A gene is part of the DNA responsible for making proteins. We get one copy of each gene from our mother and one from our father. This is how we get inherited traits, such as looks, eye color and build. Genes that have abnormal changes, or mutations, can increase the likelihood of certain diseases.
DNA is packaged into chromosomes, each of which contain a long strand of DNA with many different genes. Every cell in the human body contains 23 such chromosome pairs. Twenty-two of them are numbered chromosomes, while the 23rd is known as either an XX or XY chromosome—this is, of course, the chromosome pair that determines our gender. Each pair of chromosomes is made up of one chromosome from the mother and one from the father.
Types of Genetic Testing
In a health care setting, there are a variety of reasons one might get a genetic test. There are several types of genetic testing:
Newborn screening: This is the most common type of genetic testing. Every state requires newborns to have a screening to detect the presence of certain genetic and metabolic abnormalities that could lead to specific conditions, such as congenital hypothyroidism or sickle cell disease. In the event the screening detects worrisome abnormalities, treatment can begin immediately.
Diagnostic testing: For patients who are experiencing certain symptoms, a genetic test may be part of the diagnostic process. For example, genetic testing may be able to confirm a suspected case of cystic fibrosis.
Predictive testing: Also called pre-symptomatic testing, a healthy person may undergo this type of test because he or she has a family history of a certain hereditary disease. For example, some types of colon cancer and breast cancer can be caused by specific gene mutations.
Carrier Testing: This may be done to detect recessive or hidden genes for certain hereditary diseases. The abnormal genes can be passed silently from generation to generation without detection. This testing can be done for persons considering pregnancy either preconceptually or once pregnant. If both partners of a pregnancy carry the same abnormal gene, then there is a 25% chance the fetus can have the disease.
Pharmacogenetics: This type of testing can help determine what medication may be most effective to treat specific conditions.
Prenatal testing: Prenatal testing can determine if there are specific mutations in a baby’s genes, such as the ones that cause Down syndrome.
Preimplantation testing: For people trying to become pregnant through in vitro fertilization, the embryos may be screened for genetic abnormalities before they are implanted in the uterus.
How is the Test Conducted?
A genetic test is generally a very safe and painless procedure. It may be done by taking a sample of blood, hair or skin. Some of the most common testing procedures include:
Blood sample: This is similar to getting blood drawn for a cholesterol screening; a needle is inserted into the vein on the arm and a tube of blood is taken. For newborn screenings, the baby’s heel is pricked and a small sample of blood is taken.
Cheek swab: This simply involves taking a cotton swab and rubbing it on the inside of the cheek to get a biological sample.
Amniocentesis: For prenatal testing, the doctor inserts a thin needle through the abdominal wall to retrieve a small amount of amniotic fluid (the fluid that surrounds the fetus) for testing. This test may also be conducted by taking a tissue sample from the placenta.
For any of these tests, the tissue or fluid sample is analyzed in a lab, where technicians look for changes in chromosomes, proteins or DNA.
Predictive Genetic Testing: Pros & Cons
Genetic testing can be invaluable in helping us learn about our health. If someone is suffering symptoms and the cause is unknown, a genetic test can help physicians arrive at a diagnosis. A genetic test to assess the efficacy of certain pharmaceuticals on a patient can lead to more effective disease treatments.
Predictive, or pre-symptomatic, testing raises unique issues that require significant thought and consideration. “Just because predictive genetic testing is possible does not mean it is for everyone,” says Dr. William Maxwell, an obstetrician and gynecologist. “There are significant pros and cons to sort through with your doctors and your family.”
If you have family history of a disease or condition that can be caused by specific genetic mutations, it may make sense to consider a genetic test. It is something you should discuss with your doctor, who may refer you to a genetic counselor or provide genetic counseling directly. The scenario below describes some of the considerations to be thought through in this process.
Nearly 13% of women will, at some point in their lives, be diagnosed with breast cancer, the most common cancer to affect women apart from skin cancer. A key risk factor for getting breast cancer is a family history of the disease.
A woman who has a family history of breast cancer, in consultation with her doctor, may consider screening for BCRA1 and BCRA2, inherited gene mutations known as the breast cancer genes. For this scenario, the patient opts to go forward with the genetic screening after careful consideration.
If the genetic testing reveals that she does in fact have the gene mutation, it could be a good thing because she now knows she has heightened risk for breast cancer. She may, on the advice of her physicians, begin having more frequent breast cancer screenings. Doing this could lead to an earlier detection of the disease – should it ever materialize – resulting in faster treatment and an increased likelihood of survival.
Another possible outcome in this scenario is that the physician recommends specific medications to reduce risk. In this scenario, medications that minimize the effects of estrogen or reduce estrogen production may be considered, as estrogen can fuel the growth of breast cancer cells.
Identifying dangerous gene mutations may also create a new motivation to adopt positive lifestyle changes, such as improved diet and increased exercise levels.
Finally, a strong family history of breast cancer combined with a positive test for breast cancer genes may lead a woman to opt for a prophylactic mastectomy – a preventative removal of the breasts – a procedure that would dramatically (though not completely) reduce the odds of ever getting breast cancer.
As you can see, in this example, a genetic test for the breast cancer gene can lead to several proactive measures the patient can take to reduce her risk. At the same time, there are downsides.
A positive test inevitably leads to some degree of worry, dread and fear. If the genetic test result leads to the patient living in fear for the rest of her life, is it worth it? After all, even with heightened risk, there is no guarantee she will ever actually get breast cancer.
And will a positive test lead to emotionally difficult decisions, such as whether to have a preventative mastectomy?
Will it affect decision-making about bearing children?
All of these difficult questions must be considered.
Conversely, a negative test result can bring about an enormous sense of relief to the patient and her family. However, a negative test is no guarantee that the patient won’t still end up with the disease later. Would a negative test result create a false sense of security?
Although not common, sometimes a genetic test may also be inconclusive. The ambiguity of the result can be frustrating and does nothing to ease fears or help develop a proactive mitigation strategy.
While the health and emotional factors are the most important when considering genetic testing, another consideration is cost. Many genetic tests are relatively inexpensive, but some can cost thousands of dollars. Insurance plans may cover some of the cost, but this is certainly something you want to learn on the front end.
When it comes to privacy, federal law prohibits employers and health insurers from discriminating against someone on the basis of a genetic test. This prohibition does not apply to life insurers and some other types of insurance, however.
How to Get a Test
If you think genetic testing might be something you are interested in, you should make an appointment and discuss the issue with your doctor. While there are several commercial direct-to-consumer (at-home) tests you can purchase, only one has been approved by the Food & Drug Administration (FDA) for health testing, and only for a limited set of health conditions. Some at-home test makers assert that they can test for certain health conditions they have not been approved for by the FDA, so it is best to ask your doctor before purchasing anything.
“Genetic testing can be a valuable tool in our toolkit to help us better understand how to protect our health,” says Dr. Taylor Bradley, an obstetrician and gynecologist. “But it is also not a tool that everyone needs to use. Visit with your doctor to discuss the pros and cons so you can make the best decision for you and your family.”
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