It's a phrase used in countless movies where someone is infected with a strange disease: "Could be anything. We'll have to run more tests."

On-screen we watch a series of medical tests, each of increasing complexity, each leading us closer to the answer. The tension mounts. You go for popcorn. However, off-screen, for an ill patient nothing could be more frustrating than being subjected to a series of medical tests that produce no conclusive results.

Genetic testing is the ultimate utopian vision of the future: a quick painless medical procedure that could save your life, determine pre-natal disease risks, diagnose a disease before it happens, catch a criminal, indicate the best treatment path, or predict whether a cancer will spread or remain dormant. But is the promise of genetic testing living up to its hype?

What is Genetic Testing?
One of the earliest forms of medical analysis used by the father of medicine, Hippocrates, was the analysis of the four bodily humors. Humoral theory is the theory that all illness in the body springs from an imbalance in the four bodily humors. In Hippocrates' time, the four humors were blood, black bile, yellow bile, and phlegm. Each of these four components was inspected by their physical properties such as color and consistency and a diagnosis was made.

This type of medical analysis represents an important branch of testing: diagnosis. Indeed, the majority of medical testing techniques are diagnostic in nature. They don't predict future ailments; they identify a disease after you are infected by it.

As for prevention and prediction there are a few guidelines that a physician can give you. For example, with age, your risk of a heart attack will increase. If you are a man with high cholesterol, your risks are even higher.

These sort of recommendations are of the observational type and they are based on mortality statistics which are gathered over many years. Some of them can even be based on select demographics.

What about the cases that fly in the face of established medical wisdom? For example, in one Iranian family, researchers found that despite a long family history of premature death due to coronary heart disease, certain family members showed no signs of increased risk. What explains this contradiction? This is one such question that preventative genetic testing hopes to answer.

Genetic testing is a method of examining the human genome (the sum of your encoded genetic information in your DNA and sometimes, RNA) using complex algorithms that can predict and detect diseases in ways never before possible.

The Types of Genetic Testing
Genetic testing is far from limited to diagnosing existing diseases. Genetic testing is actually a broad term that can be broken down into seven basic categories:

• Clinical Genetic Testing, which focuses on detecting current or future diseases.
• Pharmacogenomics, which focuses on determining the viability of a particular drug-based treatment
• Identity Testing, which is sometimes used in criminal investigations, most famously in the O.J. Simpson Trial
• Paternity Testing, which determines the parent of a child, and used daily on day-time talk shows such as the Maury Povich show
• Tissue Typing, which allows physicians to assess the compatibility of tissue transplants
• Cytogenics, which is the analysis of chromosomes
• Infectious Disease Testing, which can determine an individual's susceptibility to a particular disease.

Of most interest to a patient trying to determine which disease they have now (or in the future) is Clinical Genetic Testing (CGT). In CGT, the tests are designed to look for specific gene mutations that are attributed to an increased risk in getting a specific disease. For example, in women, doctors test for genes BRCA1 and BRCA2 to determine your risk of developing ovarian or breast cancer.

What Types of Diseases is Genetic Testing Able to Detect?
Genetic testing is a hotbed of scientific curiosity and research. There are now literally hundreds of genetic tests available to doctors and even more are available to researchers. The web site www.genetests.org is currently the de facto repository of genetic testing information. Among some of the prevalent disorders genetic testing is able to detect and predict are:

• Cystic Fibrosis
• Breast Cancer
• Ovarian Cancer
• Down's Syndrome
• Huntingtons Disease
• Hypertrophic Cardiomyopathy
• Phenylketonuria
• Sickel-cell trait
• Tay-Sachs disease
• Alzheimer's disease

But is Genetic Testing Safe?
To the layperson, genetic testing might seem like an infallible fortress of scientific wisdom. The mere mention of genetic testing evokes reverence and commands credibility. The assumption guiding these thoughts is the notion that each test is rigorously verified and consistently produces conclusive results. Such assumptions, however, are not well founded.

Unlike Hippocrates, these new tests do not look at the current physical manifestations or warning signs of a disease. They look at our makeup----our genetic code. A lens that seems infallible by design.

Although there are currently more than 1000 types of genetic tests available to doctors, only a small percentage of those tests have been subject to scrutiny and held accountable for the results that they claim to produce.

Unlike prescription drugs, genetic tests are not subject to regulation by the FDA, which verifies that a specific test is able to produce specific and conclusive results. In fact, more often than not, the tests are so complicated and the analysis algorithms so sophisticated that doctors are unable to draw meaningful conclusions.

A notorious British study conducted in 2003 claimed that approximately 95 percent of the proposed links between genes and their respective diseases were without merit. In fact, rather than looking at genes, the study suggested that diseases were more than the sum of our genes, but rather a complex interaction between genes and lifestyle. In other words, genetic testing is no magic bullet.

What are the Most Useful Genetic Tests?
Genetic testing offers the promise of a remarkably accurate window into the pathology of disease. Currently one of the only FDA-approved genetic tests is the MammaPrint test, which is able to determine the likelihood that early stage breast cancer will return within five to ten years after treatment.

While the MammaPrint test is a remarkable step forward in reliable genetic testing, it's not without its own disclaimers. According to the FDA's Dr. Steve Gutman, "The test is far from perfect." Says Dr. Len Licthtenfeld, of the American Cancer Society of the test, "The test isn't any better than other tests that do the same thing. The thing that makes it stand out is its FDA approval." Lichtenfeld also notes that he doesn't feel that the test is accurate enough to be used by doctors in determining treatment options for patients.


For additional reference you may find the following links useful:

• The Universe of Genetic Testing

• An Overview of Genetic Testing at Medline Plus

• Genetic testing for genetic disorders: Weigh benefits and risks

• A repository of genetic testing information

• A Brief Primer on Genetic Testing