Genetic test is defined as "the analysis of human DNA, RNA, chromosomes, proteins and certain metabolites in order to detect heritable diseases-related genotypes, mutations, phenotypes, or karyotypes for clinical purposes."1
In other words, a genetic test is a specific type of medical test doctors use to detect changes in your chromosomes, genes or proteins. These changes, if present, are usually related to a certain type of disease, which means that the results of a genetic test confirms or rules out the presence of this disease. Genetic tests can also be used to determine passing on a genetic disorder to your children
Genetic tests are used by doctors for several reasons. Some of these are:
- Determination of genetic diseases in unborn babies
- Finding out if people carry a gene for a disease and might pass it on to their children
- Screening embryos for disease
- Detection for genetic diseases in adults before the mutations cause symptoms
- Confirming a diagnosis in a person who has disease symptoms
It is important to note that the majority of clinically validated genetic tests today look at single genes and are used to diagnose rare genetic disorders. Moreover these tests are traditionally performed only in healthcare institutions with the support of physicians and genetic counselors that decide which tests are needed in the first place. However, with the recent explosion of genomic data, as described below (History of genetic testing), and the availability of these data to the public, an ever growing number of new genetic test are being developed and offered to the general public. This tests usually look at multiple genes and try to determine person's increased or decreased risk for developing a variety of different diseases. But are these genetic test any good?
Choosing the right genetic test
With the explosion of genetic tests mentioned above it is important to note that despite the many scientific advances in genetics, researchers have only identified a small fraction of the genetic component of most diseases. What this means it that these genetic tests base their results on weak and limited scientific information that in the majority of cases does not produce valid and useful results. First of all they usually only look at the genetic profile (different low-penetrance mutations in a number of genes) of the individual but disregard other factors, such as family history, current medical status and life style choices, that are often even more important for the development of common diseases (diabetes, cardiovascular diseases, cancer, obesity) then low-penetrance mutations.
Second of all, customers receive their result on-line or over the e-mail and are often left to interpret the results themselves without any proper consultation with a healthcare professional (doctor or genetic consultant). This can lead to misinterpretation of results which can in turn have not only emotional but also social and financial consequences. More about the ethical considerations of genetic testing is explained in the Ethics of genetic testing.
5 things you should do before you decide for genetic testing:
- Inform yourself if your genetic testing provider offers you clinically useful tests
- Check that test have all the certificates needed
- Inform yourself where the analysis is performed
- Make sure that your personal data is securely saved and that your DNA is destroyed after the testing
- Genetic testing provider has to enable you genetic testing counseling in case you have any additional questions or you need guidelines
Benefits of having genetic testing
It is always important to consider to what extent an individual in going to benefit from genetic knowledge before a genetic test is considered. For example, a genetic test for Huntington’s disease exists for a long time and can determine whether a person will develop this disease in their adult life. But since there is no known cure for it are you willing to live with this knowledge? Another example are the off-the counter genetic tests discussed above. A negative result for let’s say cardiovascular diseases (or any other complex disease) is great, but as you know by now only genetics is included in these test. Living an unhealthy lifestyle even if having no mutations will not therefore spare you from cardiovascular diseases.
Regardless of this, genetic tests when they provide you with accurate, clinically relevant and helpful data also have benefits. A positive result for a specific mutation that is known to be disease causing can direct a person to have more regular checkups or change their life style in order to decrease the likelihood of developing the disease. On the other hand a negative result can relive a person from uncertainty and in some cases also eliminate further checkups and other tests. Especially important are genetic screens in newborns, where doctors can determine genetic disorder early in life and treatment can be started before any damage is done. Some further issues about genetic testing can also be found in on the Ethics and Genetics web page.
A brief history of genetic testing
Genetic testing is a relatively young discipline in medicine that has evolved in tight connection with discoveries in genetics. The first steps were made in the 1950's when the structure of DNA (deoxyribonucleic acid), the carrier of genetic information, was determined by James Watson and Francis Crick. Further discoveries were made through the 1960's and 1970's including methods on DNA isolation from cells and tissues as well as DNA analysis. However, one of the most important steps, also for the field of genetic testing, came in 1983 with the discovery of a technique named PCR for polymerase chain reaction.
PCR is a very simple method that uses the basic characteristics of DNA and enables scientists to make millions of copies of a single gene. This of course is a huge advantage in genetic testing, where doctors usually work with very small amounts of DNA. For example, let's say a doctor took a cheek swab from a patient. The amount of DNA present on a cheek swab is very very small and mutations cannot be determined directly on the isolated DNA. Therefore, DNA molecules are firstly amplified and then searched for any mutations present. For this reason PCR remains as one of the most popular techniques in genetic testing and is one of the most widely used techniques in diagnostic laboratories.
With the development of these techniques and the ever growing knowledge of the human genome, more and more diseases were linked to specific mutations in genes. The first diseases for which genetic tests were developed included cystic fibrosis, Duchenne muscular dystrophy and Huntington Chorea.
Another important leap forward was the completion of the Human Genome project, which formally began in 1990 and was completed in 2003, 2 years ahead of its original schedule. The Human Genome Project was an international effort whose goal it was to determine the sequence of the human genome and with that all the genes it contains. This eventually led to the development of genetic tests for more than 2000 diseases.(CDC)
1 - Wylie Burke, 2002, Genetic Testing, New England Journal of Medicine
2 - Center for Disease Control (www-cdc.gov)