Precision Medicine is one of the tools available for diagnosing genetic diseases and hereditary predisposition. Obtaining a diagnosis or knowing your genetic predisposition to develop certain diseases can allow you to consider specific treatments or make better decisions about screening and other risk factors, including lifestyle habits. Here are some examples of the use of precision medicine in connection with genetic disease screening:
Screening genetic testing targeting genetic diseases
These tests are performed when the disease is known, whether it is a personal diagnosis or a family history. We estimate that humans have around 20,000 genes, and clinical genetic testing is currently available for just under half. Moreover, the same disease can be associated with different genes. For example, hereditary breast cancer can be associated with the genes BRCA1, BRCA2, PALB2, CHEK2, etc. Finally, for the same disease, there are several types of analyzes that can be offered.
- Targeted test: analyzes the presence or absence of a variant previously identified in the family;
- Genotyping: A specific number of pathogenic (disease-causing) variants are analyzed in one or more genes. If you compare a gene to a book, genotyping is a bit like reading just a few words from a few selected pages. The information is therefore limited since all the rest of the content is not analyzed;
- Sequencing: the complete reading of one or more genes in order to identify genetic variants.
- Depending on the test performed, the result obtained does not always provide a simple “yes or no” response. A result can be positive, negative, inconclusive or uncertain (variant of uncertain significance or SUVs);
- Depending on your diagnosis or if you have a family history, a negative result does not entirely rule out the possibility of an inherited disease since:
- Some mutations are still unknown;
- Depending on the test performed, certain genes or mutations may not have been analyzed;
- Some genes are still unknown.
Even in the absence of a personal or family history, it is now possible to detect genetic predispositions for certain diseases, such as certain cancers and certain cardiovascular diseases (e.g. hypercholesterolemia) which have hereditary forms. Recently, numerous studies have shown that this type of screening identifies mutations in a significant number of individuals and that the majority of them have no known family history of the disease in question. The advantage of this screening is that it makes it possible to set up options for targeted screening and / or risk reduction and thus to carry out prevention.
- Genetics are not the complete answer: other factors impact your health.
- Example: You get a DNA test result identifying that you carry a pathogenic variant in a gene associated with high cholesterol. You have an increased risk of having high cholesterol. On the other hand, this risk is modified by your level of activity, your diet, your biological sex, your ethnicity, your other health problems and your environment. All of these factors affect your overall risk for high cholesterol.
- Test results for disease-predisposing genes usually tell you about high or low health risk – but the risk is not certain.
- Example: Your genetic result shows that you do not carry pathogenic variants in genes associated with hereditary breast cancer. While this is reassuring, it is not a guarantee that you will not develop cancer in your lifetime. Other factors, including age, lifestyle habits (eg smoking, alcohol, physical activity, diet) contribute to the risk of developing cancer during your lifetime.
A genetic counselor can help you navigate the gray areas and other uncertainties that you may have.
- A genetic counselling meeting looks at your family and personal history to determine if a test might help you, and if so, the counselor will help you consider the right test and understand your results;
- A genetic counselor can help you understand the limits of scientific knowledge that impact your DNA test results and offer you ways to incorporate this information into your health care;
- If you get an uncertain test result (SUV), advances in science may clarify its meaning in the future. A genetic counselor can stay on top of the latest data and can be your source for updates that could impact your health.
Exploring your genetics can be exciting, but also difficult if you’re not comfortable with strangers. Having access to a supportive health care professional can make a positive difference, and a genetic counseling meeting could help.
Nathalie Bolduc, MSc, CGAC, CGC
Certified genetic counselor