Examples of Genetic Tests in Medical Practice
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Targeted therapies for Breast Cancer
Jane, a 50 year old woman, has been diagnosed by her physician with an advanced form of breast cancer. Her doctor recommends that she start chemotherapy immediately. After a number of weeks, however, she does not respond to treatment.
Her physician remembered hearing about how the drug, Herceptin® can greatly increase the effectiveness of chemotherapy in situations where the cancer has a certain overactive gene, “Her2/neu”.
- Jane’s doctor promptly takes a biopsy, and instructs the laboratory at the hospital to test the tissue sample for Her2/neu activity. The lab results indicate that Jane’s biopsy sample shows an overproduction of Her2/neu.
- Jane and her physician discuss this new information, and further medical interventions are determined. The team decides that in Jane’s specific case, chemotherapy should be continued, but that Herceptin® would be effective as part of the treatment for Jane’s cancer.
- Weeks later, her physician reports that her tumor is responding to the new treatment program. The genetic test helped Jane’s physician tailor her treatment, and avoid some of unpleasant side effects that her prior treatments had caused.
Predicting the effectiveness of HIV therapies
Elizabeth, a 25 year old woman, has recently been diagnosed with HIV. Elizabeth’s doctors know, and HIV research has shown, that the virus that causes the infection can undergo changes its genetic make-up. In some cases, these changes cause the virus to becomes “resistant” to certain treatments. Elizabeth’s primary care physician wants to start her on HIV therapy, but before deciding which drugs should be prescribed, more information about the type of HIV virus causing her infection is needed.
- Elizabeth is referred to the clinic’s laboratory so that the appropriate tests can be conducted. When the test is completed, the results are sent to the doctor as well as a notice to Elizabeth.
- Genetic analysis of Elizabeth’s particular strain of HIV shows no mutations that indicate the virus is resistant to standard anti-retroviral therapy. Within a day, Elizabeth has her results and is able to discuss them with her physician, who reviews the most recent information about the effects of this treatment on other HIV patients.
- Elizabeth is reassured to find information explaining that her treatment can work, and hopefully will enable her to live knowing her disease is under control. Her physician acknowledges that the right treatment will be used and that Elizabeth has been offered high-quality care in a timely fashion.
Identifying risks with cancer treatments
Carlos is a 50-year-old man has recently been diagnosed with metastatic colon cancer. His oncologist begins to treat him with a drug called fluorouracil. However, after several treatments the drug has had little effect. As a result, Carlos’ doctor would like to try a new treatment with a drug called irinotecan, which has been shown to be effective when fluorouracil treatment has failed. In some individuals, irinotecan can cause damage to the body’s defense system by reducing the number of white blood cells. Whether irinotecan will have this effect in a patient, however, can be pre-determined by looking for a genetic change gene called UGT1A*28.
- Carlos is sent by his doctor to the hospital’s laboratory, where they administer the genetic test. The results come back abnormal showing that Carlos is at an increased risk for developing the negative side-effects of irinotecan.
- After careful discussion with his physician, Carlos begins treatment with the standard dosing regimen of irinotecan, but will simultaneously be monitored very closely for any negative impacts on his immune system.
Identifying proper dosage requirements
Richard is a 75 year old man who has just been diagnosed with an irregular heartbeat called “Atrial Fibrillation”. His heart specialist knows that this condition causes the heart to flutter and pump blood abnormally, possibly leading to blood clots which could cause stroke and other problems.
His specialist is considering the use of a drug called warfarin for treatment, and tells Richard that there can be serious problems such as bleeding if too much of the drug is taken each day. For some patients, Richard’s doctor won’t prescribe the medication for fear that possible complications are too risky. The heart specialist is aware of the latest medical advances, and knows that a genetic test is now available which provides a way to determine the best dosage for each patient. In fact, Richard’s doctor notices that the Food and Drug Administration recently advised following specific information on the package insert before prescribing the medication.
- Richard is tested at the hospital laboratory, and the results are sent to Richard’s physician along with a notification to Richard. By comparing the results of the genetic test with other relevant factors, including weight, age, gender, and other medications, the physician decides upon an initial starting dose of warfarin.
- Richard is closely monitored to determine the clotting tendency of his blood and any increased liver damage. Depending on the results of this monitoring, the warfarin dosage is adjusted appropriately.
- Richard’s doctor notes that since the new test has been available fewer patients have had problems with bleeding, and more people are taking the appropriate medicines for their heart problems. Richard is relieved to know he is getting the best treatment available and considers the test to have been a safety net for his care.
Newborn screening of genetic disorders
Mark and Jennifer Jones recently gave birth to Sarah, a seemingly healthy newborn baby girl. During the pregnancy, the Jones’ physician learns that both Mark and Jennifer have relatives who have been diagnosed with cystic fibrosis. Cystic fibrosis is a hereditary disease, and the Jones’s physician recommends that Sarah be tested for the genetic abnormalities that lead to the disease later in life.
- A small sample of Sarah’s blood is taken and sent to the hospital laboratory. The hospital laboratory analyzes 87 of the most common genetic mutations that can lead to Cystic Fibrosis.
- Unfortunately the tests conclude that Sarah, although not currently displaying any symptoms, will contract the disease early in her life.
- After receiving these results, Mark, Jennifer, the Jones’ doctor, and a genetic counselor discuss the results. The doctor reviews all the medical options for a young child who has cystic fibrosis, and stresses how a well-balanced, high-calorie, high-protein diet can help manage many of the symptoms.
- The Jones’ take the doctor’s advice to heart, and follow his advice in the care and early upbringing of Sarah.
Genetic-screening to identify therapeutic risks
Katie, a 25 year-old graduate student, was involved in a serious car accident and rushed to the emergency room to undergo surgery.
- While preparing Katie for surgery, her physician noted in her medical records that a genetic test showed she had genetic mutations for a cardiac channelopathy called malignant hyperthermia. Cardiac channelopathies are potentially fatal disorders caused by a number of genetic mutations that affect heart function.
- Katie had taken steps to minimize the symptoms of her disorder, however, these symptoms can be triggered during periods of stress or in combination with certain anesthetics. Katie’s physician understood the implications of her genetic tests, and used an alternative anesthetic procedure
- This avoided a potentially dangerous situation which would have triggered Katie’s disorder, and may have resulted in death.