 Large Text | | Uses of Genetic Testing | What are the uses of genetic testing which may be important for me to know? Diagnostic Testing
Diagnostic testing is used to identify or confirm the diagnosis of a disease or condition in a person or a family. Diagnostic testing gives a "yes" or "no" answer in most cases. It is sometimes helpful in determining the course of a disease and the choice of treatment. Examples of diagnostic testing include chromosome studies, direct DNA studies, and biochemical genetic testing. Predictive Genetic Testing
Predictive genetic testing determines the chances that a healthy individual with or without a family history of a certain disease might develop that disease. There is predictive testing available for some adult-onset conditions (those diseases which manifest themselves in adulthood) such as some types of cancer, cardiovascular disease, and some single gene disorders. Presymptomatic Genetic Testing
Presymptomatic genetic testing is used to determine whether persons who have a family history of a disease, but no current symptoms, have the gene alterations associated with the disease. Carrier Testing
Carrier testing is performed to determine whether a person carries one copy of an altered gene for a particular disease. The disease may be autosomal recessive, which means that the disease is present in an individual only if two copies of the altered gene are inherited. Couples who both carry the same autosomal recessive gene have a one in four, or 25 percent, chance with each pregnancy to have a child with that disease.
A recessive disease may also be X-linked recessive, which means that the altered gene is located on the X chromosome. Since females have two X chromosomes, and males have one X and one Y chromosome, females can be carriers of a gene on the X but are not affected (provided the other X has the normal copy of the gene). On the other hand, males are usually affected with the disease, if they have the altered gene on their X chromosome (because they do not possess the normal copy of the gene on the Y chromosome). Therefore, "carrier testing" for X-linked conditions is usually done in females. Prenatal Diagnosis
Prenatal diagnosis is used to diagnose a genetic disease or condition in the developing fetus and includes maternal serum screening, ultrasound (sonograms), amniocentesis, chorionic villus sampling (CVS), and percutaneous umbilical blood sampling (PUBS).
preimplantation studies
Preimplantation studies are used following in vitro fertilization to diagnose a genetic disease or condition in an embryo before it is implanted into the mother's uterus. Newborn Screening
Newborn screening is performed in newborns in state public health programs to detect certain genetic diseases for which early diagnosis and treatment are available. |
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One of the purposes of this Healthy Aging column is to keep readers aware of various strategies to live longer and lead more productive, healthy lives. One important subject to explore is the relationship between health, disease and genes. And, should we undergo genetic testing as a strategy for healthy aging? A great deal of information has been learned about the relationship between health and genes. In fact, the entire human genome has been mapped. Unfortunately, research reveals little information about genetic makeup and the cause of disease, but there are a few important facts that we should be aware of. For example, the table below lists several adult diseases that have genetic markers suggesting vulnerability to disease. Genetic testing can be done on blood, tissue, and other specimens such as a mouth swab and saliva. More than 1,000 genetic tests are available from testing laboratories. Who Should Be Tested
People who have a family history of certain types of cancer are at increased risk and may want to consider testing. Anyone else interested in genetic testing should consult with his or her doctor. Some cancers, such as colon and breast cancers, have genetic markers. Therefore, genetic testing for BRCA1, BRCA2 and HNPCC (hereditary non-polyposis colorectal cancer) in people with a family history of these cancers can provide vital information. People who find out that they are predisposed to these cancers should undergo periodic screenings to detect early cancers. Who Should Not Be Tested
Most people should not undergo genetic testing for economic, medical, ethical and other reasons. Economic reasons include the cost of testing. In addition, a worrisome test result might cause the cost of a person’s medical insurance to increase. A medical reason to avoid genetic testing is that researchers still have many unanswered questions about the role that genes play in the development of disease. Although a person's genes may make him or her more susceptible, factors such lifestyle, diet and environment also can influence the development of many fearsome diseases. In short, the presence of one abnormal gene may or may not predict a life-threatening disease. Many physicians discourage testing unless researchers have developed a clear medical response to the presence of a predisposing gene. After all, if you cannot do anything about preventing or detecting a disease, why would you want to know that you could one day develop it? For instance, would you want to test for apolipoprotein E genotype, which is known to predict Alzheimer’s disease? If you have the gene, there is no way to prevent or treat the disease. In addition, lab errors, such as false positives or false negatives also can occur with any test. Finally there is the question of ethics. For instance, if a person learns that they have the gene marker for breast cancer, should they tell anyone? Many family members, employers and insurers may insist that they have a “right to know.” But, do they?
The Bottom Line
Genetic testing may not be a good option to assist most of us with healthy aging. We should try other things first, such as exercising and eating a healthy diet. However, some of us who have family history of a disease with both a genetic marker and medical intervention should consider genetic testing. Table: Adult Diseases That May Be Predicted
By Genetic Testing | | • Amyotrophic lateral sclerosis (ALS; Lou Gehrig's Disease; progressive motor function loss leading to paralysis and death) | | • Alzheimer's disease* (APOE; late-onset variety of senile dementia) | | • Inherited breast and ovarian cancer* (BRCA 1 and 2; early-onset tumors of breasts and ovaries) | | • Hereditary nonpolyposis colon cancer* (CA; early-onset tumors of colon and sometimes other organs) | | • Central Core Disease (CCD; mild to severe muscle weakness) | | • Duchenne muscular dystrophy/Becker muscular dystrophy (DMD; severe to mild muscle wasting, deterioration, weakness) | | • Dystonia (DYT; muscle rigidity, repetitive twisting movements) | | • Hereditary Hemochromatosis (HFE; excess iron storage disorder) | | • Huntington's disease (HD; usually midlife onset; progressive, lethal, degenerative neurological disease) | | • Marfan Syndrome (FBN1; connective tissue disorder; tissues of ligaments, blood vessel walls, cartilage, heart valves and other structures abnormally weak) | | • Mucopolysaccharidosis (MPS; deficiency of enzymes needed to break down long chain sugars called glycosaminoglycans; corneal clouding, joint stiffness, heart disease, mental retardation) | | • Myotonic dystrophy (MD; progressive muscle weakness; most common form of adult muscular dystrophy) | | • Polycystic Kidney Disease (PKD1, PKD2; cysts in the kidneys and other organs) | | • Adult Polycystic Kidney Disease (APKD; kidney failure and liver disease) |
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