In 2003, publication of the complete sequence of the human genome capped a decade of explosion in genetic knowledge. Later that year, researchers announced that much of this information had been placed on a single, dime-sized glass slide called a DNA microarray or gene chip. This tool allows researchers to rapidly examine humankind’s estimated 35,000 genes so they can pinpoint those linked to disease, an achievement that promises to transform the practice of medicine in the near future.
One day gene chips may be used to generate individual genetic profiles that can quickly predict a person’s risk of many common and potentially deadly medical problems, including breast cancer, colon cancer, diabetes, heart disease, and stroke. These high-tech devices may begin to appear in your doctor’s office within the next decade or so.
In the meantime, you can harness the genetic information locked in your genes with one of the most basic and effective tools known to medicine: a detailed and accurate family history. By learning as much as you can about your own family’s health history, you can open a window on your genetic inheritance and better assess your risk of certain diseases —which can open up a path to prevention of a disease or its early detection.
A Family History: What Your Relatives Reveal
A good family history should cover the health history of as many of your first- and second-degree relatives as possible for at least three generations. Once you have compiled a family history, look for patterns that may point to a predisposition for certain diseases in your family. Items to flag include a relative who died of an illness at an early age, several relatives who developed the same cancer, more than one type of cancer in a relative, and occurrence of the same disease in more than one generation.
Believing that this information could be better utilized in preventive medicine, the Centers for Disease Control and Prevention (CDC) recently launched a Family History Public Health Initiative. Its goal is to harness the predictive power of the family history by developing a standardized, computer-based survey that people can complete at home or in their doctors’ offices. This family history information would then be analyzed to assess the person’s level of risk for one or more diseases.
The initial diseases to be covered in this family history initiative are heart disease, stroke, diabetes, breast cancer, ovarian cancer, and colon cancer. These conditions were chosen because family history is an established risk factor for each disease, relatives are generally aware of the disease among family members, effective preventive measures are available, and the disease is a significant public health burden.
Once a patient is found to be at risk for a particular disease based on the health history of close relatives, a physician can recommend appropriate preventive measures, which might include more frequent screenings, changes in diet, increased exercise, weight loss, and drug therapy.
Harnessing Your Family History
A good family history focuses on as many first-degree relatives (parents, siblings, and children) and second-degree relatives (grandparents, grandchildren, aunts, and uncles) as possible.
Presenting the information in a chart can help to highlight vulnerabilities. Include as much information as you can about any illness each relative might have had, particularly those that may be preventable, such as heart disease, high blood pressure, diabetes, alcoholism, and depression. When possible, also note the age at which each disease was diagnosed, the age when each relative died, and the cause of death. If you are unable to obtain this information from family members, it may be helpful to consult death certificates, which are usually available from the municipality in which a person died.
Is Genetic Testing in Your Future?
If your family history indicates an unusually high risk of a particular condition, your doctor may suggest considering genetic testing. “Someone who has several family members, say parents or siblings, with colon cancer—and particularly if the cancer developed before age 50—should think about having genetic testing,” advises Frank Giardiello, M.D., Professor and Chief of Gastroenterology at Johns Hopkins.
From a purely practical point of view, the responsible gene (or genes) must be known and a suitable test must be available. In addition, effective preventive measures and therapies should be available in case they are needed. There is usually little value in knowing you are highly vulnerable to a particular condition unless you can do something to prevent or treat it.
People with certain hereditary cancers will probably be the first to benefit from genetic testing. Although these cancers account for only 5% to 10% of all malignancies, identifying affected families can have a major impact on the health of those who are at risk. Based on current research, genetic testing is most likely to be recommended for hereditary forms of the following diseases.
Genetic Testing for Colon Cancer
Scientists have identified several genes that increase the risk of developing two types of hereditary colon cancer: familial adenomatous polyposis (FAP) and hereditary nonpolyposis colorectal cancer (HNPCC). People with FAP have hundreds, or even thousands, of polyps in the colon and nearly always develop colon cancer by age 40 unless their colon is surgically removed. Thus, they can benefit from aggressive monitoring and treatment.
People who carry one or more of the gene mutations responsible for HNPCC have an 80% risk of developing colon cancer during their lifetime. Furthermore, women with this mutation also have a 40% to 60% lifetime risk of endometrial cancer and a 10% lifetime risk of ovarian cancer. Genetic testing for HNPCC can produce significant benefits by identifying candidates for more intensive screening since annual colonoscopy can greatly reduce the risk of dying of colon cancer. More aggressive monitoring and, perhaps, prophylactic surgery could also reduce mortality from endometrial and ovarian cancer associated with HNPCC mutations.
Because a gene mutation for colon cancer occurs more frequently in people of Ashkenazi Jewish ancestry than in the general population, genetic testing for hereditary colon cancer might also be recommended for people with this ethnic background if they have multiple colon polyps or a family history of colon cancer.
Genetic Testing for Breast Cancer
Women who inherit specific mutations in BRCA 1 or BRCA 2 genes are at increased risk for hereditary breast cancer and ovarian cancer. Someone who has a strong family history of breast or ovarian cancer, particularly when it occurs among close relatives under the age of 50, might consider genetic testing. People found to carry the BRCA 1 or BRCA 2 genes could then make better-informed decisions about surveillance and early detection and treatment of the associated cancers.
Going Forward with Genetic Testing
Ultimately, experts agree that genetic testing will transform medical care for many diseases, including noncancerous conditions such as heart disease and diabetes, and that using gene chips to assess risk of several conditions may one day be routine.
According to Dr. Giardiello, “In the future, I think we’re going to test people for the 15 to 30 genes that we think have anything to do with colon cancer. In about 10 years, we’ll take a drop of your blood, put it on a gene chip, and tell you what your profile is in terms of colon cancer and several other diseases.”
Genetic Testing and Protecting your Privacy
Although the highly specific information that genetic testing can provide promises to transform medical care for the better, this vital personal information potentially could be used to deny people access to health insurance or employment in a way that a basic family history cannot. Federal legislation passed in 1997 provides some protections: Insurers cannot use genetic testing information to charge different individual premiums within a group plan, for example, and people carrying a specific mutation cannot be viewed as having a preexisting condition. More comprehensive Federal legislation is pending. Many states also have passed legislation to protect people against genetic discrimination and to ensure the privacy of genetic information.
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