Genetic Testing
Genetic testing is a procedure that generally is performed to test whether a person carries genes for certain inherited disorders. For the screening of actual changes in the sequence of a person's DNA (deoxyribonucleic acid), the tests involves the analysis of small samples of blood, skin or other tissues. Instead of DNA tests, it is also possible to carry out biochemical tests that would indicate certain changes in blood protein profile or the build up of metabolites in tissues as an indication for further tests. The human genome is thought to code for some 20,000 - 25,000 genes. With more than 3,000 genes identified, and over 4,000 known diseases caused by genetic defects, genetic testing has become an increasingly important part of medical practice. About 900 such tests are currently available and more are being developed.
DNA, genes and genome
All living organisms have DNA (deoxyribonucleic acid, a double copy helix molecule) in their cells, often in a confined structure that is called the nucleus. The DNA molecules function as a library, it is the organism's genetic blueprint. DNA molecules can be very long containing millions of repetitive elements, called nucleotides (guanine, adenine, thymine and cytosine). It is the exact order of these nucleotides that forms instructions for making the materials (proteins and RNA molecules) which an organism needs to function. The DNA sequence also includes the information that is involved in regulating the use of this genetic information. The segments of DNA that are associated with the synthesis of real cellular components are called genes. Other parts of the DNA may be used to shape it into folded structures (chromosome) or have a function in determining when genes must be active.
The instructions in genes allow living cells to make proteins. Proteins can be used as structural parts of the organism, they can have a role in regulating cellular processes or they may be involved in catalysing chemical reactions. In the latter case the protein is called an enzyme. It is clear therefore that a single gene cannot code for a wing or a complete structure such as an eye. However, there are genes that have a crucial role in the initial steps when eye formation starts or how the shape of the wing will look like.
If the DNA molecule, or a chromosome in germline cells (egg cell, sperm cell) is damaged (spontaneously, by the influence of chemicals or as the result of radiation), it may be repaired with the help of its copy in the helix structure, or by 'filling in' missing nucleotides, or by re-bonding a broken DNA molecule. In the last two cases, it is possible that the damaged DNA region was part of a gene that now codes for a protein that may have been changed, which in turn could affect its function. The defective gene may be transmitted via the germline cell to progeny. In the worst case scenario, a single defective gene may already cause a person to have a diseased condition.
Microarry technology allows the simultaneous genotyping of up to 100,000 different patients in a single testReasons for genetic testing
- Diagnostic genetic testing can be carried out if physical symptoms are thought to be connected to a genetic defect. The outcome can be used to manage the condition.
- New parents can be tested for a (combination of) specific genetic or chromosomal aberration if an increased risk of having a baby with a genetic or chromosomal disorder is suspected. The suspicion is often based on known family data.
- Newborns can be tested routinely for genetic diseases that occur frequently or for genetic diseases that run in the family. The outcome of the test can influence the way the condition would need to be managed. The test could also be done in early pregnancy if serious conditions would justify abortion.
- In vivo fertilisation is a complex and costly procedure, therefore genetic tests can be used prior to embryo implantation to optimise the results.
- Forensic testing is not used to identify genetic aberrations, but instead finds matches between persons and samples found at a crime scene.
- Researchers use genetic testing for a variety of reasons: one of them would be the finding of new markers for so far unknown genetic diseases.
Ethical, Legal, and Social Issues
The outcome of a genetic tests may have implications for employment and insurance. Therefore it is important to safeguard the rights of individuals to maintain privacy and access to results should be limited to those authorized to receive it. It is also important to have knowledge of the risks, benefits, effectiveness, and alternatives to testing in order to understand the implications of genetic testing.
Genetic testing is a complex process, and the results depend both on reliable laboratory procedures and accurate interpretation of results. Tests also vary in sensitivity and specificity, therefore the interpretation of test results is often complex even for trained health care specialists. When interpreting the results of any genetic test, one must take into account the probability of false positive or false negative test results.
About the film
Analysis of our genes enables us to make statements not only about ourselves, but also about our blood relatives. Who should have access to this information and under what conditions? This is the core question addressed by the film. Today, hundreds of genetic tests can provide information about our health, and the number is rapidly growing. In the privacy of the doctors office such information is important for the diagnosis of diseases and even to identify predisposition to diseases that we may or may not develop in the future. But outside of the doctors office, such information could, if unchecked, lead to discrimination. The film looks at the specific case of private health and life insurances and explores what actions we as society can take to protect our privacy.
