What kinds of genetic tests are there?

Genetic tests can be divided into three general categories depending on their purpose:

• Diagnostic tests: These tests are mainly used to find the cause of an existing disease.
• Predictive tests: These tests are used to determine whether a person has certain characteristics that, for instance, influence the effectiveness of a drug, or that may lead to the development of a disease in conjunction with certain environmental factors. Predictive tests can help to plan treatment.
• Prognostic tests: These help to predict your risk of getting a disease in the future. They can also indicate the likelihood of a genetic trait or a condition being inherited by your children.

Genetic testing isn't only used for medical purposes. It is also used in research, as well as in forensics and paternity testing.

What does the testing involve?

Your genetic information can be found in the chromosomes inside the nucleus of the cells that make up your body. These chromosomes consist of helix-like DNA strands. This is why genetic testing is also known as DNA analysis. Genes are individual segments of a DNA strand.

Blood cells are commonly used for genetic testing. A standard blood sample is all that is needed. Sometimes, hairs on your body or cells from the mucous lining of the mouth are tested too. The latter can be taken from inside your cheek using a cotton swab.

The genetic information from the cells is then isolated, and the sequence of the chemical building blocks that make up all genes can be read using special techniques. The different genes and changes within genes can be detected by comparing the sequences of the building blocks.

This analysis is done at a certified laboratory. It may take several weeks for the results to come back.

What are the effects of genetic mutations?

Genes can have a number of different functions. Each one usually contains the blueprints for a specific protein. Every protein has a special purpose, such as regulating part of the body's metabolism or assisting in cell division. When genes mutate (change), “their” proteins may change too. They might then no longer be able to function correctly, which could have various effects, such as disrupting the body's metabolism. Other genetic changes may cause a cell to make a protein that isn't supposed to be made at all. Because proteins do so many different things, the effect that a change has on your general health depends on the exact nature of the change.

The complete disappearance of a protein due to a genetic mutation is often very noticeable: There are thousands of known genetic diseases caused by a genetic mutation leading to the lack of a specific protein.

Other genetic changes only have slight effects on your health. These will then often depend on other genes, as well as lifestyle and environmental factors. This is one reason why genetic testing can only rarely be used to make predictions about health issues with a high level of certainty. Genetic testing is often no more conclusive than other tests.

What is genetic testing used for?

Genetic testing can help answer questions such as:

How and when are gene tests discussed?

In Germany, genetic testing is governed by the Genetic Diagnosis Act (Gendiagnostikgesetz). This act determines which tests are allowed, when they are allowed, and what information has to be provided by the doctor beforehand. The Genetic Diagnosis Act also stipulates that no genetic tests may be done without the express written consent of the person being tested.

Your doctor must talk with you about what is going to happen during the procedure, and describe any risks and possible consequences of the test. You should also be given an appropriate amount of time before the test to consider what you have been told. It's important to know that you have a right to not know.

In addition to the information your doctor is obligated to give you, the Genetic Diagnosis Act stipulates that special genetic counseling should be offered on the possible medical, psychological and social consequences of a genetic test – for instance if the test shows you have a higher risk of getting an incurable disease. Exactly when this genetic counseling should be offered depends on the type of genetic testing to be done. For some genetic tests (such as those that are done before birth), counseling is required before the procedure. For other tests, it is needed only once the results are in.

Counseling should be easily understandable, allow you to decide for yourself what to do next, and also let you know where you can find support for physical and mental issues. Genetic counseling is offered by many practices that also perform genetic testing. According to the Genetic Diagnosis Act, this kind of counseling can only be conducted by doctors who have specialized in human genetics or who have additional qualifications in this area.

What are the risks of genetic testing?

Like with any test, the results of genetic testing should be interpreted with caution. Usually, only the most common genetic changes are detected, but not all. Even if a mutated gene is found, it's often not possible to reliably predict whether and when a disease may develop. Conversely, a “normal” (negative) test result can't provide absolute certainty that a disease won't occur.

The risk of diseases like diabetes, asthma, high blood pressure or coronary artery disease can be influenced by your genes, but usually mostly depends on environmental conditions and individual lifestyle factors. So the results of genetic testing for those diseases aren’t very conclusive.

Knowing that you have genetic risk factors for a disease that can't be treated or cured is distressing and can cause anxiety. This is the case for conditions like hereditary forms of Alzheimer's disease or the neurological disorder Huntington's disease.

Further information:

If you face the decision of whether or not to have genetic testing, you have the right to information and counseling about the possible consequences. The following things may be helpful for people living in Germany:

• Genetic counseling: This is offered by specialized doctors and genetic counseling centers.
• The directive on genetic counseling, published by the Genetic Testing Committee (Gendiagnostik-Kommission): This directive stipulates which conditions doctors must meet in order to offer this kind of counseling and what specific topics need to be discussed.
• Genetic Diagnosis Act (Gendiagnostikgesetz): Brief summary available (in German) on the website of the German Federal Ministry of Health, for instance.

Sources

• Gesetz über genetische Untersuchungen bei Menschen (Gendiagnostikgesetz, August 2013).
• Deutsche Krebsgesellschaft. Familiärer Krebs – Wie viel liegt in den Genen? September 10, 2014.
• Deutsches Referenzzentrum für Ethik in den Biowissenschaften, Prädiktive genetische Testverfahren. January 2014.
• Aretz S, Propping P, Nöthen M. Indikationen zur molekulargenetischen Diagnostik bei erblichen Krankheiten. Dtsch Ärztebl 2006; 103(9): A-550/B-473/C-453.
• Bundesministerium für Gesundheit. Glossar: Gendiagnostikgesetz. October 12, 2015.

• IQWiG health information is written with the aim of helping people understand the advantages and disadvantages of the main treatment options and health care services.

  Because IQWiG is a German institute, some of the information provided here is specific to the German health care system. The suitability of any of the described options in an individual case can be determined by talking to a doctor. We do not offer individual consultations.

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