Genetics investigates how certain biological traits and characteristics are transmitted through generations and families. Molecular medicine on the other hand, examines how illnesses and diseases occur & can be prevented at the cellular or molecular level.

People have known for many years that living things inherit traits from their parents. Genes are responsible for carrying our traits through generations. They are made of deoxyribonucleic acid (DNA). But genes themselves dont do the actual work. Rather, they serve as instruction books for making functional molecules such as ribonucleic acid (RNA)and proteins, which perform the chemical reactions in our bodies. Genes are often called the blueprint for life, because they tell each of your cells what to do and when to do it: be a muscle, make bone, carry nerve signals, and so on

Many, if not most, diseases have their roots in our genes. Genes - through the proteins they encode - determine how efficiently we process foods, how effectively we detoxify poisons, and how vigorously we respond to infections. More than 4,000 diseases are thought to stem from mutated genes inherited from ones mother and/or father. Common disorders such as heart disease and most cancers arise from a complex interplay among multiple genes and between genes and factors in the environment.

Gene testing involves examining a persons DNA - taken from cells in a sample of blood or, occasionally, from other body fluids or tissues - for some anomaly that flags a disease or disorder. The DNA change can be relatively large: a missing or added piece of a chromosome - even an entire chromosome - that is visible under a microscope. Or it can be extremely small, as little as one extra, missing, or altered chemical base. Genes can be over expressed (too many copies), inactivated, or lost altogether. Sometimes, pieces of chromosomes become switched, or transposed, so that a gene ends up in a location where it is permanently and inappropriately turned on or off.

In addition to studying chromosomes or genes, genetic testing in a broader sense includes biochemical tests for the presence or absence of key proteins that signal aberrant genes.

Genetic tests can be used to look for possible predisposition to disease as well as to confirm a suspected mutation in an individual or family.

Predictive gene tests look for disorders that "run in families" as the result of a faulty gene that is inherited. These tests are presently available for diseases such as Tay-Sachs disease and cystic fibrosis. Gene tests are also being developed for many more conditions, including a predisposition to ALS, oramyotrophic lateral sclerosis, the fatal nerve degeneration known as Lou Gehrigs disease; Huntingtons disease, a devastating disorder of middle age that causes dementia and ends in death; some forms of Alzheimers disease; and catastrophically high cholesterol.

Genes have also been found for several types of cancer that can run in families.

People in high-risk families live with troubling uncertainties about their own future as well as that of their children. A negative test - especially one that is strongly predictive - can create a tremendous sense of relief. A negative test also may eliminate the need for frequent checkups and tests such as annual colonoscopy (a procedure that allows a physician to view the upper reaches of the large intestine), which are routine for high-risk families concerned about cancer.

A positive test can also produce benefits. It can relieve uncertainty, and it can allow a person to make informed decisions about his or her future.

Under the best of circumstances, a positive test creates an excellent opportunity for counseling and interventions to reduce risk.

The decision to undergo gene testing is a very personal one. It should also be voluntary. A person should agree to the test only if he or she desires the information. No one considering a gene test should be pressured into it by relatives, health care providers, or anyone else. In addition, unless test results can lead to direct medical benefits, experts advise parents to avoid making this choice for their children. The decision to have a gene test should be left to the individual, at a time when he or she is mature enough to weigh the options and handle the results. Because the issues are so complex and the consequences so profound, the decision to have a genetic test deserves careful preparation and thought.