Precision Medicine

What Is Precision Medicine?

Precision medicine — also called "personalized medicine" or "genomic medicine" — is a way to guide the prevention, diagnosis, and treatment of diseases based on the person's individual genes, environment, and lifestyle.

What Do Genes Have to Do With Precision Medicine?

The launch of precision medicine came when the international Human Genome Project successfully sequenced the human genome — "decoding" human DNA and identifying the genes that it contains. Most of our cells contain a complete set of DNA, the operating instructions that influence everything from a person's hair color to susceptibility to disease.

• A genome is a living thing's genetic material — a complete set of DNA, containing all of the genes the body needs to develop, grow, and maintain itself.
  • DNA is the hereditary material in all living cells; each cell in the body contains about 6 feet of DNA thread. DNA is wrapped together to form chromosomes. Most cells have 23 pairs of chromosomes, for a total of 46.
  • Genes are sections or segments of DNA carried on chromosomes that determine specific human characteristics (like height and hair color). As cells duplicate, they pass this genetic information to the new cells.
• Sequencing means figuring out the exact order of base pairs in a segment of DNA. Bases are the "building blocks" of DNA that store the information in our genes. Genes, along with things in our environment (like diet and exercise), combine to produce an individual's phenotype — the group of traits (characteristics) that determine how the person's body looks and works (like the enzymes needed to digest food or the pigment that gives eyes their color).

What Are the Benefits of Precision Medicine?

Precision medicine helps health care providers better understand the many things — including environment, lifestyle, and heredity — that play a role in a patient's health, disease, or condition. This information lets them more accurately predict which treatments will be most effective and safe, or possibly how to prevent the illness from starting in the first place.

How Does Precision Medicine Work?

Let's use cancer as an example:

Patient Smith is diagnosed with cancer. Doctors use diagnostic tests (biopsies, lab tests, etc.) to "grade" the cancer; for example, to see how large a tumor is or whether the cancer has spread.

Now, for patients with some kinds of cancers (such as breast, lung, colorectal, melanoma, and leukemias), molecular genetic testing can be a tool to guide more individualized and effective care. The testing finds differences (called mutations) in the genes in the person's cancer cells. This helps doctors decide which treatments might improve survival and minimize side effects.

Drug treatment decisions for some diseases, like cystic fibrosis, is another example of precision medicine in action:

Cystic fibrosis is a genetic chronic disease that leads to severe lung problems and damage to other organs and body tissues. Molecular genetic testing has shown that many different gene mutations can cause it. A new (and very expensive) drug developed to treat cystic fibrosis is only effective in people who have certain specific gene mutations causing their disease. So genetic testing of patients with cystic fibrosis can help doctors identify which patients benefit from treatment with the drug.

Are There Problems or Limitations With Precision Medicine?

Although use of a person's genetic profile to guide health care decisions will certainly become more common and helpful as time goes on, there are a number of issues to consider:

• Currently, genetic mutation information that can guide medical decisions exists for only a small number of diseases and conditions — but this is expanding rapidly.
• It will take time for doctors to learn about and become comfortable with using this genetic information as a new tool for patient care.
• There is some concern about privacy issues and how the genetic information might be used (for example, could a health plan charge a higher premium for or deny coverage to a person who is found to have a gene mutation that might increase his/her risk for getting a disease?).
• Many genetic tests are very expensive and health insurers are reluctant to cover them unless there is clear evidence that doing the test will benefit the patient. However, as the use of genetic testing becomes more common — and better (and cheaper) tests are developed — the price for tests should decrease.

Should My Child Have Molecular Genetic Testing?

It depends on your child's condition, and whether there is a genetic test available that's helpful for making a decision about your child's diagnosis or treatment. If you have questions about this, ask your child's doctor. Genetic testing is most appropriately performed with the help of genetic counselors or geneticists, who are trained in the evaluation of molecular tests and their results and implications.