About Family Genetics

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July 15, 2005 at 12:28 pm  •  Posted in Family Genetics by  •  0 Comments

Introduction
What Is Genetic Testing?
What Genetic Tests Are Used in Prenatal Screenings?
How Is Testing Used With Newborns?
How Are Genetic Tests Used to Predict Cancer?
What Are the Limitations of Genetic Testing?

 

Introduction

Our genes determine our physical appearance, our personality, how our body functions, and other characteristics that make each person unique. Each of us inherits from our parents as many as 35,000 different genes.

As genes are passed down from generation to generation, medical conditions and diseases, or the increased risk for disease, tend to run in families due to gene abnormalities. Health care professionals now better understand how irregular genes are passed from one generation to the next and have an increased ability to test for hundreds of inherited illnesses.

What Is Genetic Testing?

Through DNA samples of small quantities of blood, skin, hair, or other tissues or fluids, scientists can identify defective genes that may indicate future health problems. A genetic defect in one specific gene, for example, can cause an inherited disorder such as cystic fibrosis, sickle cell anemia, or Tay-Sacs disease.

It is now known that abnormal inherited genes are also responsible for an increased risk for certain types of cancer, diabetes, Alzheimer’s disease, Parkinson’s and other common diseases that were not always linked to genetic factors.

Many mental illnesses may be the result of simultaneous changes in several different genes. An estimated 50 to 75 percent of depression is inherited, according to the Nemours Foundation, but the specific genes linked to depression have not yet been found.

Genetic testing is commonly used in unborn fetuses, newborns, and people who have a high risk of developing a particular disease due to a strong family history of the disorder. Some couples who are planning a pregnancy may decide to have a genetic test to determine their chance of passing on a genetic disorder to their children. Tests are also used to confirm a diagnosis so doctors can formulate an effective treatment plan.

What Genetic Tests Are Used In Prenatal Screenings?

Prenatal tests determine the risk for genetic disorders and physical deformities. Parents over age 35, parents with a family history of a genetic disorder, and pregnant women who have been exposed to harmful chemicals may consider prenatal testing.

Common prenatal tests include the triple screen of the mother’s blood to test for Down syndrome, spina bifida, and other genetic disorders and an amniocentesis, a test of the amniotic fluid. The percutaneous umbilical blood sampling test can detect sickle cell anemia, hemophilia, and anemia.

Prenatal testing can provide information that is not available through regular prenatal health visits. Pregnant women will want to weigh the risks of testing, such as pain, worry, and the possibility of a miscarriage, with the value of knowing what the tests may find.

How Is Testing Used With Newborns?

Blood samples from newborns are routinely tested in hospitals to identify rare metabolic disorders that could result in seizures, stunted growth, or life-threatening conditions. The types of tests required are mandated by state law.

More than 25 different medical conditions can be identified through sampling a few drops of blood taken from a baby’s heal. Every state requires the testing of phenylketonuria (PKU) that, if left untreated, can result in mental retardation and seizures. When the condition is caught early, doctors can prescribe a diet that will prevent medical problems or minimize complications.

Early diagnosis of medical conditions is important in helping parents to understand the health issues that their newborn will face and to consider genetic testing to address the possibility that future children may be born with the same condition.

How Are Genetic Tests Used to Predict Cancer?

Women who are at higher risk of developing breast or ovarian cancer due to the incidence of cancer in one or more close relatives and other factors may consider genetic testing to identify abnormal genes that are linked to cancer risk.

Genetic testing can be useful in guiding health care; for example, women who have a particular gene mutation have a significantly higher risk of developing cancer: a 65 percent chance of developing breast cancer, compared with a 12 percent lifetime risk for most women, according to Mayo Clinic. This information will help a woman and her physician determine the appropriate prevention and early detection strategies.

Having a family history of breast or ovarian cancer does not necessarily indicate that the illness is hereditary or that the mutated gene has been passed on. Inherited breast cancer makes up only 5 to 10 percent of all breast cancers.

Women who test positive for genetic mutations can begin preventive strategies, such as exercising, losing excess weight, and taking a medication to reduce cancer risk. In addition, early detection measures are vital, such as regular mammograms and physical examinations.

Many people are not aware that men can also get breast cancer. Detailed family medical history and genetic information is also important for men to be aware of so they can receive appropriate screening and medical care.

What Are the Limitations of Genetic Testing?

Like all medical tests, genetic testing is not 100 percent accurate. Positive tests don’t predict the exact probability of developing a disease or the severity of the disease if it develops. Genetic tests are continually being developed and improved, but they may not detect all of the complex mutations that could cause a disease. In this case, a false negative test could provide a false sense of security. Likewise, a false positive test could promote unnecessary worry and concern.

Individuals who are deciding to undergo genetic testing are encouraged to seek accurate information about all of the benefits and risks involved.

Genetic counseling services are available to help individuals and families with the decision-making process. If genetic testing is pursued, genetic counselors can help calculate the risks, decipher the test results, identify medical management issues, and provide various types of support. Physicians can refer patients to genetic counselors or to a genetic counseling center in the community.

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