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Genetic Screening

By

Jeffrey S. Dungan

, MD, Northwestern University, Feinberg School of Medicine

Last full review/revision Dec 2019| Content last modified Dec 2019
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Genetic screening is used to determine whether a couple is at increased risk of having a baby with a hereditary genetic disorder. Hereditary genetic disorders are disorders of chromosomes or genes Overview of Chromosome and Gene Disorders Chromosomes are structures within cells that contain a person's genes. A gene is a segment of deoxyribonucleic acid (DNA) and contains the code for a specific protein that functions in one or... read more that are passed down from generation to generation.

  • Screening involves assessing the couple’s family history and, if needed, analysis of blood or tissue samples (such as cells from the inside of the cheek).

Any couple can request genetic screening, but screening is particularly recommended when

  • One or both partners know they have a genetic abnormality.

  • Family members have a genetic abnormality.

  • Partners belong to a high-risk ethnic group.

Family History Assessment

To determine whether a couple has an increased risk of having a baby with a genetic disorder, doctors ask the couple about the following:

Information about three generations is usually needed. If the family history is complicated, information about more distant relatives may be needed. Sometimes doctors review the medical records of relatives who may have had a genetic disorder.

Carrier Screening

Carriers are people who have an abnormal gene for a disorder but who do not have any symptoms or visible evidence of the disorder.

In carriers, the abnormal gene is usually recessive—that is, two copies of the gene are needed to develop the disorder (see Recessive Disorders Recessive x-linked disorders Genes are segments of deoxyribonucleic acid (DNA) that contain the code for a specific protein that functions in one or more types of cells in the body. Chromosomes are made of a very long strand... read more ). Such carriers have one normal gene and one abnormal gene for the disorder.

Only women can carry an X-linked (sex-linked) recessive gene. Women have two X chromosomes. Thus, on the other X chromosome, the corresponding gene may be normal and protect women from developing the disorder. Because men have only one X chromosome, all men who have an abnormal X-linked recessive gene have the disorder that the abnormal gene causes.

Carrier screening involves testing people who do not have symptoms but are at higher risk of carrying a recessive gene for a particular disorder. Risk is higher when one or both partners have a family history of certain disorders or have characteristics (such as ethnic background or racial or geographic group) that increase the risk of having certain disorders. However, screening is done only if the following criteria are also met:

Carrier screening usually consists of analyzing the DNA from a blood sample. But sometimes a sample of cells from the inside of the cheek is analyzed. People provide the sample by swishing a special fluid in their mouth, then spitting it into a specimen container, or by rubbing a cotton swab inside their cheek.

Ideally, carrier screening is done before a woman becomes pregnant. If it is done afterward and if it indicates that both partners have a recessive gene for the same disorder, they may decide to have prenatal diagnostic testing Prenatal Diagnostic Testing Prenatal diagnostic testing involves testing the fetus before birth (prenatally) to determine whether the fetus has certain abnormalities, including certain hereditary or spontaneous genetic... read more . That is, the fetus may be tested for the disorder before birth. If the fetus has the disorder, treatment of the fetus may be possible, or termination of the pregnancy may be considered.

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