What we are learning about our genetic makeup will change medicine forever. Scientists participating in the Human Genome Project, which began in 1990, have sequenced the 3 billion "letters" (chemical building blocks) that make up human genetic material. Their goal is to identify all 20,000 to 25,000 of our genes and learn what they do, including genes that cause disease.
What does this mean for you and your family? Doctors may soon be able to predict who is at risk for many genetic diseases, and provide treatment to prevent some of them. The number of genetic tests readily available should increase rapidly, as more disease-causing genes are identified.
In the 1980s and 1990s, scientists discovered numerous disease-causing genes, including those associated with fragile X syndrome (the most common inherited form of mental retardation), cystic fibrosis, certain heart defects, familial breast and colon cancers, and many more. These discoveries led to improvements in diagnosis and genetic counseling for these diseases and, in some cases, improvements in treatment. New and better drugs for genetic diseases will be developed, based on information about how disease-causing genes work. Treatment will increasingly be tailored to the individual because tests will show which drugs will work best for you. Gene therapy, which aims to cure a genetic disease by replacing or changing a disease-causing gene in certain cells of the body, should become available for some diseases. For you and your family, this could mean a healthier future.
Genetics and You
Now that you're pregnant, your biggest concern is probably your baby's health. Most parents-to-be swear they don't care whether they have a boy or a girl, fair- or raven-haired, just as long as the baby is healthy.
Many characteristics are determined at conception. Egg and sperm each "donate" 23 chromosomes, and the resultant 46 chromosomes form our genetic blueprint. Some pairs of genes contain one dominant and one recessive gene. For example, if your partner has curly hair and you have straight hair, your baby is likely to have curly hair because this trait tends to be dominant. Other gene pairs act together to determine a characteristic. This is the case with eye color. Two brown-eyed parents, for example, can have a child with any eye color.
Just as harmless traits like curly hair can run in families, so, too, can more harmful conditions.Birth defects occur in one of every 28 births. Sometimes, an abnormal gene can cause or contribute to the occurrence of a birth defect or genetic disease. In other cases, a birth defect can be caused by environmental factors such as alcohol abuse or infections. Often birth defects seem to reflect a combination of both heredity and environment. If one of these conditions runs in your family, you may be worried about passing it on to your baby. A genetic counselor can help determine the risk of this occurring.
What Is Genetic Counseling?
Genetic counseling helps people to identify and understand what particular traits they may pass on to their children and the likelihood that they will do so. A genetic counselor is a trained health care professional who works with a person or family who may be at risk for an inherited disease or an abnormal pregnancy outcome. Genetic counselors are experienced in helping families understand birth defects, risk, and how inheritance works.
If you go to see a genetic counselor, he or she will want to know about your family's medical history. It's okay if you don't know the answers to all the questions. The counselor may suggest blood tests, physical exams, or prenatal tests to help put together a picture of how your family's health may affect your children. For example, blood tests can determine if you and your partner are "carriers" of genes that can cause an inherited disease in your baby. In many cases, a genetic counselor can reassure you that the risk to your baby is lower than you feared.
Anyone who has unanswered questions about diseases or traits in their family should consider genetic counseling. Those who might be especially interested include:
- Women who are pregnant or planning to be pregnant after age 35. The risk of Down syndrome and related chromosomal disorders increases with age.
- Couples who already have a child with mental retardation, an inherited disorder or a birth defect.
- Couples whose infant has a genetic disease diagnosed by routine newborn screening.
- Women who have had babies who died in infancy or three or more miscarriages.
- Men or women who are concerned that their job, lifestyle or medical history may pose a risk to a current or future pregnancy. Concerns might include exposure to radiation, medications, chemicals, infections or drugs.
- Couples who would like testing or more information about genetic defects that occur frequently in their ethnic group. Examples include Tay-Sachs disease (a fatal central nervous system disease) in couples of Eastern European Jewish ancestry; thalassemia (severe anemia) in those of Mediterranean and Southeast Asian ancestry; sickle cell disease (a blood disorder) in African Americans; and cystic fibrosis (a serious disorder affecting lungs and other organs) in couples of northern European background.
- Couples who are first cousins or other close blood relatives.
- Pregnant women who, based on ultrasound tests or blood tests, have been told their pregnancy may be at increased risk for complications or birth defects.
Testing For Genetic Disorders
During pregnancy, prenatal tests can diagnose or—far more likely—rule out Down syndrome and other chromosomal errors, hundreds of genetic disorders, and other conditions that may not be genetic, such as heart defects. Your health care provider may recommend one or more tests including blood tests, ultrasound, amniocentesis, and chorionic villus sampling. Fortunately, most women who undergo these tests learn that their baby does not have the disorder for which he or she was tested.
Your health care professional may offer you prenatal tests to gain information and reassurance about the health of the baby. Screening tests may be used to identify pregnancies at increased risk for genetic disorders or birth defects and may be given even when there are no risk factors.
Click here to learn more about prenatal testing.
