People use genetic testing for several reasons. Prospective parents may want to be tested for genetic mutations that could cause genetic diseases in their children. Before prescribing certain drugs, physicians use tests to predict how a patient will metabolize that medication and whether that patient is likely to experience serious side effects. In the case of certain cancers, oncologists can test to know which therapies may be most effective for a particular patient. People with genetic diseases in their family history may benefit from knowing their likelihood of inheriting that disease. Testing DNA is a useful diagnostic tool in treating children who develop serious conditions that defy diagnosis.
The benefits of health genetic testing can generally be divided into three areas:
- Tests that help a person anticipate conditions for which they or their offspring may be at risk.
- Tests that help a patient and his or her physician decide on the best course of treatment for a particular condition.
- Diagnosing diseases
Since genomic research is very new, definitive benefits are a source of great debate and opinion. A test such as the one that identifies the BRCA1 and 2 mutations for breast and ovarian cancer is universally considered of great predictive value, and patients who test positive are urged to consider prophylactic measures. Another useful test for cancer risk is the one for hereditary nonpolyposis colorectal cancer (Lynch Syndrome).
Other tests, especially those that identify predisposition to chronic diseases such as diabetes or hypertension, are considered far less predictive. Patients who test positive for these genes will likely be counseled to make the healthy lifestyle choices they have already been urged to make by their physicians.
Genetic testing looks for specific inherited changes (mutations) in a person’s chromosomes, genes, or proteins. Genetic mutations can have harmful, beneficial, neutral (no effect), or uncertain effects on health. Mutations that are harmful may increase a person’s chance, or risk, of developing a disease such as cancer. Overall, inherited mutations are thought to play a role in about 5 to 10 percent of all cancers. So only certain changes in DNA will have an effect. There in lies the challenge to identify which changes are diseases causing in a background of constantly changing DNA sequences over a lifetime. Taking a babies DNA at birth can provide a master copy later in life that will not have all the environmental changes and strictly the inherited DNA mutations.
Cancer can sometimes appear to “run in families” even if it is not caused by an inherited mutation. For example, a shared environment or lifestyle, such as tobacco use, can cause similar cancers to develop among family members. However, certain patterns—such as the types of cancer that develop, other non-cancer conditions that are seen, and the ages at which cancer typically develops—may suggest the presence of a hereditary cancer syndrome.
The genetic mutations that cause many of the known hereditary cancer syndromes have been identified, and genetic testing can confirm whether a condition is, indeed, the result of an inherited syndrome. Genetic testing is also done to determine whether family members without obvious illness have inherited the same mutation as a family member who is known to carry a cancer-associated mutation.
Inherited genetic mutations can increase a person’s risk of developing cancer through a variety of mechanisms, depending on the function of the gene. Mutations in genes that control cell growth and the repair of damaged DNA are particularly likely to be associated with increased cancer risk.
No. Even if a cancer-predisposing mutation is present in a family, it does not necessarily mean that everyone who inherits the mutation will develop cancer. Several factors influence the outcome in a given person with the mutation.
One factor is the pattern of inheritance of the cancer syndrome. To understand how hereditary cancer syndromes may be inherited, it is helpful to keep in mind that every person has two copies of most genes, with one copy inherited from each parent. Most mutations involved in hereditary cancer syndromes are inherited in one of two main patterns: autosomal dominant and autosomal recessive.
So not all diseases are genetic based and may be environmental but without a genetic history of the families involved it will be impossible to know. As all the mechanisms involved are also not understood having the genetic record of a family will allow doctors to test for several genes in a family history which may be having a synergistic effect for developing diseases such as cancer. Also in patients who have already been diagnosed with cancer, a positive result for a mutation associated with certain hereditary cancer syndromes can influence how the cancer is treated. For example, some hereditary cancer disorders interfere with the body’s ability to repair damage that occurs to cellular DNA. If someone with one of these conditions receives a standard dose of radiation or chemotherapy to treat their cancer, they may experience severe, potentially life-threatening treatment side effects. Knowing about the genetic disorder before treatment begins allows doctors to modify the treatment and reduce the severity of the side effects.
Although cancer is often used as the example for genetic testing the same principles apply for many other diseases especially ones which don’t have an immediate discernable cause like many neurological and immunological diseases. Currently, for the patients and their loved ones, one of the most difficult aspects is getting to the right diagnosis. For many families, the diagnostic odyssey lasts years and even decades. Families trek all over the world seeking answers, looking to connect to the right specialists that can give them more clues, and directions for their diseases, often, not knowing what is wrong is one of the hardest challenges. The right diagnosis is the first foundational step that sets into motion all subsequent plans to help the patient. As there are still a lot of variations to consider, additional filtering strategies are important to isolate the possible gene or genes that are causing the illness. Since parents share 50% of the genetic makeup with their children, their genomes serve as a good filter. If both parents are normal, you can remove all the variations that are also present in the parents. If either of the parents is affected, we can look at what is shared between the people affected by the disease. This step helps filter the thousands of possible differences to tens of possible outcomes which help diagnosis. Having a grandparents DNA as a filter can narrow it down even more. Great grandparents even more.