If you have symptoms of a disease that may be caused by genetic changes, sometimes called mutated genes, genetic testing can reveal if you have the suspected disorder. For example, genetic testing may be used to confirm a diagnosis of cystic fibrosis or Huntington's disease. Presymptomatic and predictive testing. Although genetic testing can provide important information for diagnosing, treating and preventing illness, there are limitations. For example, if you're a healthy person, a positive result from genetic testing doesn't always mean you will develop a disease. On the other hand, in some situations, a negative result doesn't guarantee that you won't have a certain disorder.The variety of genetic tests has expanded throughout the years. Early forms of genetic testing which began in the 1950s involved counting the number of chromosomes per cell. Deviations from the expected number of chromosomes (46 in humans) could lead to a diagnosis of certain genetic conditions such as trisomy 21 (Down syndrome) or monosomy X (Turner syndrome). In the 1970s, a method to stain specific regions of chromosomes, called chromosome banding, was developed that allowed more detailed analysis of chromosome structure and diagnosis of genetic disorders that involved large structural rearrangements.In addition to analyzing whole chromosomes (cytogenetics), genetic testing has expanded to include the fields of molecular genetics and genomics which can identify changes at the level of individual genes, parts of genes, or even single nucleotide "letters" of DNA sequence. According to the National Institutes of Health, there are tests available for more than 2,000 genetic conditions, and one study estimated that as of 2017 there were more than 75,000 genetic tests on the market.
If you’re offered a genetic test, you may be referred to a genetic counsellor to help you think through what the test means for you and your family.
Before you have genetic testing, gather as much information as you can about your family's medical history. Then, talk with your doctor or a genetic counselor about your personal and family medical history to better understand your risk. Ask questions and discuss any concerns about genetic testing at that meeting. Also, talk about your options, depending on the test results.
If you're being tested for a genetic disorder that runs in families, you may want to consider discussing your decision to have genetic testing with your family. Having these conversations before testing can give you a sense of how your family might respond to your test results and how it may affect them.
Not all health insurance policies pay for genetic testing. So, before you have a genetic test, check with your insurance provider to see what will be covered.
In the United States, the federal Genetic Information Nondiscrimination Act of 2008 (GINA) helps prevent health insurers or employers from discriminating against you based on test results. Under GINA, employment discrimination based on genetic risk also is illegal. However, this act does not cover life, long-term care or disability insurance. Most states offer additional protection.
Genetic testing is often done as part of a genetic consultation and as of mid-2008 there were more than 1,200 clinically applicable genetic tests available. Once a person decides to proceed with genetic testing, a medical geneticist, genetic counselor, primary care doctor, or specialist can order the test after obtaining informed consent.
Genetic tests are performed on a sample of blood, hair, skin, amniotic fluid (the fluid that surrounds a fetus during pregnancy), or other tissue. For example, a medical procedure called a buccal smear uses a small brush or cotton swab to collect a sample of cells from the inside surface of the cheek. Alternatively, a small amount of saline mouthwash may be swished in the mouth to collect the cells. The sample is sent to a laboratory where technicians look for specific changes in chromosomes, DNA, or proteins, depending on the suspected disorders, often using DNA sequencing. The laboratory reports the test results in writing to a person's doctor or genetic counselor.
Routine newborn screening tests are done on a small blood sample obtained by pricking the baby's heel with a lancet.
Depending on the type of test, a sample of your blood, skin, amniotic fluid or other tissue will be collected and sent to a lab for analysis.