Genetic Screening

Laura Simenson

Copyright 1999

On the last day of February 1953, a young British scientist named Francis Crick entered the Eagle Pub, his rumored hangout, and announced that he and American, James Watson had discovered the secret of life (Shreeves 49). The secret they found was the structure of DNA, which would finally allow the properties of this tremendously important molecule to be understood.

Now more than 50 years later, the secret of life is not so secret anymore. Deoxyribonucleic acid (DNA) is the material that composes genes, which contain the hereditary material that is passed from generation to generation. The entire set of DNA in an individual is the genome, which in the human, amounts to about 80,000-100,000 genes. Each gene may work singly or in combination with other genes to code for a protein that has a specific function in the body. Proteins that digest food, give eye color, enable red blood cells to carry oxygen efficiently, and to a certain degree, even control intelligence are controlled by a gene or genes. Genes exist in different forms (alleles). The result of the specific combination of alleles is the genotype (genetic make-up) of the individual.

Sometimes mutations occur in the DNA sequence. These mutations can affect a person in negative ways that result in diseases, defects, or other general maladaptions. These defects can be hereditary and are then passed on to offspring. Scientists now have tools to predict or determine genotypes of individuals and see the polymorphisms (differences) in the DNA sequence that cause genetic variance in the population. Genetic Screening is the examination of the genetic constitution of an individual--whether a fetus, a child, or an adult--in search of clues leading to the likelihood that this person will develop of transmit a hereditary defect or disease. (Suzuki 144).

Technical Aspects of Genetic Screening

Before the development of advanced molecular analysis, the only way to determine that an individual was at risk for having or carrying a disease or trait was to consult a family pedigree. The concerned individual could then see if a particular trait "ran" in his/her family. Today, progressive techniques in molecular genetics can be used to detect minute differences in DNA that cause a person to exhibit a trait. There are two basic test types used in detecting human genetic abnormalities.

The first strategy involves the examination of bodily substances. This biochemical analysis can indirectly show the presence or absence of variant genes (Suzuki 146). Testing fetal fluids using fluorescent in situ hybridization (FISH) or amniocentesis are two ways fluids can be analyzed to show the effects of genetic variance. Amniocentesis involves testing fetal fluids to recognize detrimental disease at an early stage in human development. Cell-rich amniotic fluid is extracted from the womb to obtain information about biochemistry and chromosome number.

Because of family history of a hereditary disease, some people are at an increased risk of giving birth to a child with a genetic disorder. Certain ethnic groups with family history of disease may opt to have these tests done on the fetus of their developing child. For example, blacks have a higher risk for sickle cell anemia, and if both parents are carriers they have a 25% chance of giving birth to an afflicted child in each pregnancy. Other diseases can be detected by amniocentesis. For example, Tay-Sachs disease is a medical condition that results from the absence of an enzyme needed to breakdown certain fats. An accumulation of fat in the brain causes neurological problems and eventually death of the infant. Cystic Fibrosis is a disorder which causes mucus build-up in the lungs and reduces life expectancy. Also, some infants can be born with PKU, an enzyme deficiency affecting 1 in 15,000 babies. This condition results from the inability of the body to metabolize the amino acid, phenylalanine. The accumulation of this amino acid in the body shifts a metabolic pathway to the production of pyruvic acid. High levels of this acid can cause brain damage.

FISH is a newer method that determines chromosome numbers in fetuses. This method uses fluorescent markers as probes to find to fetal chromosomes. The markers are stained and show up as spots of light which are then counted to see if there is an error in chromosome duplication (Wingerson 62-63). Some diseases which can be detected are Turner syndrome, Klinefelter syndrome, and Down syndrome.

Biochemical screening tests have also been used on people in the workforce. They are designed to identify individuals that may be more susceptible to certain hazards, such as pollutants, chemicals, and radiation. An example given in the book, Genethics, examines the red blood cells of people born with glucose-6-phosphate dehydrogenase deficiency. These people are thought to be more susceptible to oxygen depletion when exposed to industrial chemicals such as napthalene. Employees with this deficiency could be assigned to work in a less hazardous area.

The previously discussed tests have all involved the use of body fluids as a method for detecting disease. The second strategy involves directly observing human chromosomes or chromosomal DNA. Karyotyping involves looking at chromosomes and detects chromosomal duplications similar to FISH, discussed earlier.

PCR-RFLP (Polymerase Chain Reaction-Restriction Length Polymorphism) is another technique frequently used in the lab. The process involves amplifying a piece of DNA, and mixing it with a restriction enzyme that recognizes certain sequences and cuts them at a specific site. The result is a banding pattern of different size fragments that show up on gel-electrophoresis. The banding pattern shows polymorphisms (small variances) in the DNA. The polymorphisms are observed by the presence or absence of a particular sized band that is not characteristic of an unaffected individual. These specific bands can be used as markers for disease.

Multiplex gene testing is another method that can be used to detect genetic conditions. Commonly, the term multiplex gene testing refers to the testing of multiple mutations that give rise to a single disorder. But as the Human Genome Project gets closer to completion and new tests are developed there is an increasing possibility that one test could show many different genetic disorders (The Council 15). There are three broad categories of multiplex tests:

  1. Tests that find genetic conditions that will lead to onset of an inevitable disease
  2. Tests that detect the risk of developing a certain disease or susceptibility testing
  3. Tests that determine a patients carrier status

Pros and Cons of Genetic Screening

DNA tests can provide instant information on future ailments and life expectancy; currently there are tests to detect probabilities of developing only certain diseases. These tests can have many ethical implications. How people deal with and use the information and who should have the information are issues that continue to be highly debated. The October 1999 issue of National Geographic provides a story of just how lives can be affected by these tests.

Fifty-eight-year-old Ina Savage, wife and mother, was struck with Alzheimer’s disease, a progressive and irreversible disease characterized by degeneration of brain cells. Now she can’t remember the simplest tasks; even getting dressed is a challenge.

Eight genes have been linked to Alzheimer’s disease, but there is no cure yet. Conclusive tests for the disease should be available upon the completion of the Human Genome Project. When asked if she would have a genetic test done, one of Ina’s daughters said, "It would be irresponsible not to; I want to start a family." Another daughter held a different view: "What if an insurer learned the test was positive and decided not to pay for treatment?" These statements bring up strong points on the pros and cons of genetic screening.

Screening for specific diseases can pose major advantages. With PKU, treatment can be administered to correct the disease before it becomes detrimental. Susceptibility testing is also beneficial for detecting the likelihood of developing certain cancers. If tested early enough, people can take precautions such as changing diet and exercise, and getting routine medical examinations to curb cancers of the breast and colon before the tumors become established in the body.

There is also a realistic possibility with the completion of the Human Genome Project, that people will soon be able to match up their genome and test it against a database of knowledge about diseases and implications of behavior, diet, and drugs (NAG 68). Affymetrix’s Steve Fodor states in the October 1999 issue of National Geographic that "people can begin to look for themselves at how their genetics are likely to affect everything from their eating habits to the kind of perfume they choose to wear. We think genetic information will give people more control of their lives.."

Will genetic information really give people more control over their lives? Or will their lives be controlled by genetic information? For as many reasons there are to get gene screened, there are many (if not more) reasons to not get tested. What are the negative implications of genetic screening? Some examples can be noted with insurance companies, employment, child-bearing, and dealing with possibly knowing too much about the future.

The Code of Medical Ethics, written by the American Medical Association, has specific citings dealing with ethical issues in screening of genetic disorders. The code states that all carrier testing must be voluntary, and should not be disclosed to third parties without consent of the individual being tested. Insurance companies and employers should not be allowed to discriminate against carriers of genetic disorders. However, there have been documented cases of individuals who have been turned down or charged a higher insurance premium because their genetic makeup predisposes them to the development of a certain disease.

Another negative side to genetic screening has to do with fetal testing. What happens when parents are given too much information regarding the status of their unborn child? Should parents have to decide whether or not to give birth to a child with Down syndrome or that will have cystic fibrosis? These decisions can cause emotional hardship for the family involved.

There are also justifiable concerns regarding adulthood diseases. Case in point, tests that can show if a person will develop Alzheimer’s in the future. This also can cause emotional distress on the individual as well as the family.

Can people know too much about their future? I think the most important issue in the field of genetic screening is choosing which genes we should screen. For any disease that is reversible, such as PKU, or for diseases that can be treated or risk diminished by diagnosing in early onset, knowing genetic information is extremely beneficial. However, consider the implications of knowing everything about a person’s genetic makeup. Imagine a parent telling a child, "Forget about Harvard, with your IQ genes, you’ll be lucky to make it out of high school." This seems very depressing, but is a very realistic possibility. As difficult as it may be, a line needs to be drawn between what is knowing the right kinds of information and what is knowing too much. There is a great need to establish a strictly followed genetic screen code that takes into consideration the well-being of all humans.


Albertson, T., Cons of Genetic Screening. Obtained from the WWW 10/20/99:
Code of Medical Ethics, and American Medical Association. Carrier Screening of Genetic Disorders. Obtained from the WWW 10/20/99:
The Council on Ethical and Judicial Affairs, and American Medical Association. "Multiplex Genetic Testing." Hastings Center Report. Jul-Aug. 1998: 15-21. Genetic Screening. Obtained from the WWW 10/20/99:
Kolata, Gina. "Genetic Testing Falls Short of Public Embrace." New York Times 17 March 1998 sec. A16. Shreeves, James. "Secrets of the Gene". National Geographic. Oct. 1999: 42-75. Stawicki, S., Pros of Genetic Screening. Obtained from the WWW 10/20/99: html
Suzuki, David, and Knudtson, Peter. Genethics: The Clash Between the New Genetics and Human Values. Cambridge: Harvard UP, 1990.
Wingerson, Lois. Unnatural Selection New York: Bantam Books, 1998.

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