American Medical Association Family Medical Guide - American Medical Association [662]
Screening of Newborns
Every state requires testing of all newborns for a variety of disorders 24 hours after birth and before they are released from the hospital. Some disorders have no immediate visible effects but can cause physical problems, mental retardation, or death unless they are detected and treated early. Newborn testing allows treatment for some disorders to be started early, when it is most effective. Required screenings vary by state, but most states require testing for phenylketonuria, or PKU (see page 962), hypothyroidism (see page 404), galactosemia (see page 964), and sickle cell disease (see page 613). Many states are expanding newborn screening to test for more than 40 disorders. Ask your doctor if this is an option in your state.
Carrier Detection
Some people carry genes for specific diseases that they can pass on to children. Genetic testing can identify people who are carriers of disease genes. Once a person or couple find out that they are carriers of a genetic disorder, a genetic counselor can help them understand all of their reproductive options and provide them with information to help them make decisions about family planning based on the test results.
Routine screening is offered to people who are at increased risk of having the genes for specific recessive genetic disorders because of their race or ethnic origin. For example, screening for sickle cell disease is offered to people of African descent; screening for thalassemia (see page 616) is offered to people of Mediterranean descent such as Greeks and Italians; screening for Tay-Sachs disease (see page 960) and Canavan disease (see page 960) is recommended for Ashkenazi Jews; and screening for cystic fibrosis (see page 958) is recommended for people of European descent.
Presymptomatic Testing for Genetic Disorders
Sometimes a person inherits a gene or genes for a disorder that does not have an effect until later in life. For example, a person who inherits the gene for Huntington disease (see page 969) will usually be perfectly healthy until sometime after age 30, when his or her nervous system begins to degenerate, eventually leading to death. Because the Huntington gene is a dominant gene, if a person has the gene, he or she will develop the disease and has a 50 percent chance of passing the gene on to a child, who will also have Huntington disease.
Some people with a family history of Huntington disease choose not to have the genetic test for it because they don’t want to know that they will develop a disease that is fatal and for which there is no treatment or cure. Other people decide to have the test because they do not want to live with uncertainty about their future or they want to make sure they are not at risk of passing the gene on to a child. If you have a family history of a genetic disorder that does not cause problems until later in life, talk to a genetic counselor about the benefits and risks of being tested for the gene.
A recessive genetic disorder called hereditary hemochromatosis (see page 961) is a common disease that affects many people and for which there is effective treatment. In hemochromatosis, the defective gene causes the body to store too much iron, which can lead to diabetes, cirrhosis of the liver, heart disease, and tissue damage. The disease can be managed by periodically removing or donating a specified amount of blood to reduce the level of iron in the blood. Because hemochromatosis is so common and the treatment is effective and relatively easy, some doctors believe that everyone should be tested for it.
Presymptomatic Testing for Common Disorders
Newer genetic tests are being developed to screen for genes that make a person susceptible to developing a particular disorder such as cancer later in life. These genes are called susceptibility genes because people who have