Benefits of Genetic Testing

Pre-Conception: Parental Screening

In order to decrease the number of children born with congenital defects, tests are available for many diseases that identify genetic markers in potential parents. By knowing the odds of their having an affected child, young families can make better-informed decisions and possibly explore options for starting a healthy family.
A simple test for carriers of sickle cell anemia has been identifying at-risk families since the early 1970s. Prevalent among African-Americans, the disease is caused by a mutation in hemoglobin, the oxygen-carrying protein in red blood cells. Red blood cells of affected people tend to become misshapen ("sickled") when they are deproved of oxygen. Sickle cell anemia is extremely painful and patients are at great risk for infections.

If an African-American couple is considering having children, a blood test to determine whether one or both of the parents is a carrier can aid them in deciding whether to begin a family. If both parents are carriers, there is a one in four chance that their children will have sickle-cell anemia and a one in two chance that the children themselves will be carriers.

One in 27 Jews of European descent is a carrier for the metabolic disorder Tay-Sachs Disease. Tay-Sachs results from a lack of an enzyme, hexosamindase A, which is normally responsible for eliminating fat from neural cells. If this fatty residue is allowed to build up, motor skills and mental development deteriorate, and even with the best medical care, Tay-Sachs patients die by age 5.

By incorporating Tay-Sachs screening into the process of marriage in the Jewish community, awareness has risen considerably. In fact, since the 1970s, the number of cases of Tay-Sachs has decreased by 90%.

Prenatal Testing: Just To Be Sure

After conception but before birth, it is possible to test fetuses for genetic defects. Several processes are available to check on the developing child's progress throughout the prenatal period.

During the second trimester (fourth through sixth months) of pregnancy, women can be tested for high levels of alpha-fetoprotein in their own blood. Excess of this protein indicates that the fetus may be developing with a neural tube defect such as spina bifida or that the pregnancy may end with miscarriage, low birth weight, or premature delivery.
Other procedures, such as ultrasound and amniocentesis, can be used to test the fetus for defects such as Down's Syndrome and problems with organ development.
Cancer Screening: The Two-Hit Hypothesis

As more and more research is done on cancer, it is being found that chains of cellular events lead to malignant tissue. By testing those at risk for cancers for mutations around oncogenes (genes associated with cells' transforming into tumor cells), a better picture of an individual's chances of suffering cancer can be gained.

Genetic marker screening for cancer is usually most useful when investigating families. For example, mutations in the recently isolated BRCA1 and BRCA2 genes are known to lead to breast cancer in many cases. Mutations in these genes are very prevalent among women on Ashkenazi (Eastern European) Jewish descent.
Cervical cancer is associated with infections of human papillomavirus (HPV) and mutations near the ras and c-myc oncogenes, while the tumor marker sequence CA125 is used to evaluate risk of cervical cancer.
Colon cancer results from the loss of arm q of chromosome 5, and bladder cancer is often a loss of the entire chromosome 9.
Using any of several molecular biology procedures, the state of an individual's genome with respect to cancer risk can be determined.
An overview of the advantages of genetic screening can be found at this site.
Next page: What are some problems with genetic testing?

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