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Posted on 21. July 2011

Genetic Testing: What Is it?

By Carla Schick

In recent years, genetic testing has progressed from its original perception as a futuristic science fiction idea, to a popular mainstream media topic. As members of an IG-treated community, perhaps you have paid more than the usual attention to magazine articles or TV news programs that talk about the latest breakthroughs in genetic research. But what exactly is genetic testing? What kinds of tests are involved? What sort of knowledge does genetic testing provide? Let’s try to answer these questions.

What Is Genetic Testing?
Genetic testing is a careful scientific examination of a person’s deoxyribonucleic acid (DNA) that seeks to find mutations in the genes or alterations in the level or configuration of key proteins coded for particular genes. It can be used to identify an illness in an individual with symptoms and to help to determine the possibility of developing a disease. Genetic testing is offered to the young and old alike. For example, a pregnant mother who is considered a “high-risk” pregnancy might be referred to a prenatal geneticist to undergo amniocentesis, a process in which the doctor extracts amniotic fluid from the mother’s uterus to find out if the fetus will be born with a birth defect. As with all genetic testing, abnormal results might signify that the patient may have a genetic infirmity.

What Types of Genetic Tests Are Offered?
Three forms of genetic testing are currently available: gene tests, biochemical tests and chromosomal tests.

Gene tests look for abnormalities within individual genes or short lengths of the DNA or ribonucleic acid (RNA) strands. The gene samples are extracted from a person’s blood, tissues or saliva. The tests can look for big alterations like a gene that has a missing or extra section, or mutations as small as an added, absent or altered chemical base within the DNA strand. Gene tests also have the ability to identify too many duplicates of a gene, individual genes that are overly active or tuned off, or genes that are simply not present.

Biochemical testing is quite different. You might think of this exam the next time you eat a yogurt or any other food product that contains the protein phenylalanine. Biochemical testing looks at the quantity or behavior of essential proteins. By studying the amounts or activities of these proteins, the biochemical test can decipher if there are any abnormal signs that would signal that the genes are not functioning correctly. Back to our phenylalanine protein reference: A biochemical test can detect if a person has a metabolic condition known as phenylketonuria (PKU). People with PKU do not have the enzyme that breaks down phenylalanine. As a result, phenylalanine can reach unsafe levels, which can lead to health issues. Thus, people who have PKU are highly advised to eat a diet low in phenylalanine.

Our last genetic test is the chromosomal test. This exam is probably the one that most of us are familiar with since we usually hear about it in the news. The chromosomal test is responsible for detecting disorders like Down’s syndrome, which is a malfunction of chromosome 21, or Krabbe disease, which is caused by a mutation on chromosome 14. Most humans typically have 23 pairs of chromosomes. The test looks at aspects of a person’s chromosomes, including their structure and quantity, to identify if any modifications, like a missing or expanded chromosomal section or a piece being switched to another chromosomal altogether, has taken place.

Within the chromosomal test are two sub-tests: the karyotype test and the fluorescent in situ hybridization (FISH) test. The karyotype analysis gives a broad scope or idea of what a person’s chromosomes look like, from the smallest to the biggest. This overall test can identify alterations in the quantity of chromosomes and any major changes within the DNA organization.

The FISH test, on the other hand, looks at specific regions on chromosomes using fluorescent DNA probes. Using this technique, the exam is able to locate small pieces of a chromosome that are not present or that have duplicates.

What Information Can Genetic Testing Provide?
Genetic testing can provide six different types of results for those who select to undergo this kind of analysis.

First, if you have symptoms, a genetic test can provide a diagnosis. Second, it can decipher if you are a carrier for a genetic mutation. Third, a prenatal amniocentesis can determine if a fetus will be born with a birth defect. Fourth, newborn screening can identify any missing or abnormal proteins that can cause illness. Fifth, genetic testing can determine if a person has an inherited disposition for a particular condition. And last, pharmacogenetics, the study of a person’s response to various drugs, can determine the right kind or dose of medication that is best for a specific individual.

Genetic testing is a fascinating subject that has garnered a lot of interest and recognition over the years. What are your thoughts on genetic testing?

Below is a link to the information found in this blog.
www.genome.gov/19516567#al-2

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Categories: Need to Know

Comments (2) -

Eugene Richardson
8:00 AM on Saturday, July 23, 2011

Great article.  Was wondering however why few doctors ever refer patients for genetic testing.  What could the patient do to make this happen.  Having lived now for 43 years with chronic inflammatory demyelinating polyneuropathy and Peripheral Autonomic Neuropathy resulting in severe disability, no doctor ever suggested genetic testing to see if a genetic form of neuropathy was responsible.  Why?  Is there something a patient should ask that may spark this idea in the doctor?  Where do they send you or to what kind of doctor?  I communicate with hundreds of undiagnosed neuropathy patients with severe symptoms and very few ever are sent for genetic testing.  Any ideas as to why this is so?

tmitschang
11:07 AM on Monday, July 25, 2011

Eugene,

Thank you for your comment and questions. Some autoimmune diseases have known genetic causes. However, many autoimmune diseases are thought to be the result of several factors, including possible multiple gene defects. It is hoped that with the advances made in genome sequencing we will have more answers that will help make genetic testing for autoimmune diseases a valuable tool in the future. For now, however, unless there is a known genetic test for your particular disease, genetic testing is probably not yet an option for most patients with an autoimmune disease.

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