Taking the guesswork out of genetic testing

A genome is the total of an individual’s genetic material. The genome consists of chromosomes made from very long strands of DNA. Each human has 23 pairs of chromosomes. Half are inherited from the mother and half from the father.

Susan Locke

Chromosomes are organized into many subunits; the subunit is called a gene. There are 30,000 to 50,000 genes in an individual’s genome. The specific combination of genes that an individual has makes up his/her genetic identity known as a genotype.

By 2003, scientists were able to identify every gene in a human’s body. Scientists then began to look at the genes to try to pair them with the medical problems that they cause. There are many diseases that are thought to be caused by alterations (mutations) in DNA. These alterations can occur spontaneously or be inherited.

Some of the diseases with a genetic component include Alzheimer’s disease, breast cancer, ovarian cancer, colon cancer, leukemia, lymphoma, bone marrow disorders and others.

There are seven main reasons that genetic testing is performed: clinical testing to determine current or future disease; pharmacogenomics used to assess therapeutic drug treatment; identity testing (also known as “DNA testing”) used for criminal investigations or forensic studies; parentage testing (paternity testing); tissue typing for transplantation; cytogenetics (chromosome analysis, often performed on pregnant women); and infectious disease testing to determine how much viral material is still in the body after treatment.

Questions arise about the use of home genetic testing, such as “23andme.” The test can tell you if your odds of getting a certain condition are better or worse than the general population. The results you receive from this should be reviewed with your doctor. Data from 23andme can be helpful in its assessment of how a person may metabolize certain drugs.

Your results from a testing service like this should be carefully evaluated. Even if your results indicate that you possess a certain version of a gene, it does not mean that you will develop the disease.

These tests may tell you the chance of developing a certain genetic disorder, but not conclusively that the disease will develop. When a test detects a problem gene, it also cannot predict how severely the person will be affected if he or she develops the disorder.

Many diseases are a result of the interaction between genetics and environment. For example, lifestyle plays an extremely important role in who will develop heart disease. It is important to ask your physician about steps you can take to mitigate risk factors associated with any potential disorders.

There are a few other factors to consider before deciding whether to get genetic testing. There is a psychological component to testing. While having a negative test can be reassuring, a test indicating that you have a gene that predisposes you to an increased risk of a disease could be psychologically traumatizing. On the other hand, it could also lead to positive changes in lifestyle. Legally, it is possible that the results of the genetic testing could be used to determine insurance coverage.

If you do get genetic testing, the most important thing is to work with an expert to understand your test results. Most doctors are not trained to interpret these results. Genetic counselors and/ or a geneticist can help with the interpretation and implications of these complicated tests.

SUSAN LOCKE is Healthnetwork Foundation’s medical director.

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