0.4 About the controversal ethical issues on applications of  (Page 5/6)

• carrier screening, which involves identifying unaffected individuals who carry one copy of a gene for a disease that requires two copies for the disease to be expressed;
• preimplantation genetic diagnosis;
• prenatal diagnostic testing;
• newborn screening;
• presymptomatic testing for predicting adult-onset disorders such as Huntington's disease;
• presymptomatic testing for estimating the risk of developing adult-onset cancers and Alzheimer's disease;
• confirmational diagnosis of a symptomatic individual;
• forensic/identity testing.

In gene tests, scientists scan a patient's DNA sample for mutated sequences. A DNA sample can be obtained from any tissue, including blood. For some types of gene tests, researchers design short pieces of DNA called probes, whose sequences are complementary to the mutated sequences. These probes will seek their complement among the three billion base pairs of an individual's genome. If the mutated sequence is present in the patient's genome, the probe will bind to it and flag the mutation. Another type of DNA testing involves comparing the sequence of DNA bases in a patient's gene to a normal version of the gene. Cost of testing can range from hundreds to thousands of dollars, depending on the sizes of the genes and the numbers of mutations tested.

Gene testing already has dramatically improved lives. Some tests are used to clarify a diagnosis and direct a physician toward appropriate treatments, while others allow families to avoid having children with devastating diseases or identify people at high risk for conditions that may be preventable. Aggressive monitoring for and removal of colon growths in those inheriting a gene for familial adenomatous polyposis, for example, has saved many lives. On the horizon is a gene test that will provide doctors with a simple diagnostic test for a common iron-storage disease, transforming it from a usually fatal condition to a treatable one.

Genetic DNA testing to evaluate paternity/parentage or forensic/identity testing is possible because our biological characteristics are passed from generation to generation following the basic rules of inheritance. These rules have been known for more than a century. Deoxyribonucleic acid (DNA), which is a very stable and strictly inherited molecule, encodes all genetic information and determines our biological characteristics. Modern DNA paternity testing relies on the fact that we can detect and study "DNA markers" at specific structural regions of the DNA. Many different DNA markers exist in the general population. However, only two such DNA markers exist in any one individual. A child inherits one DNA marker from the mother and one from the father. A DNA test begins by learning which DNA markers are present in the child and the mother. It is then possible to determine which of the child's DNA markers was inherited from the mother and which was inherited from the biological father. To evaluate paternity and complete a paternity test, a series of DNA tests is performed on the biological specimens provided by the mother, child, and alleged father. When the DNA Profiles™ of this trio are compared to each other, the paternity test will provide two possible results; the alleged father will be either included or excluded as the biological father of the child.