Since the completion of the Human Genome Project in April of 2003, researchers have been making major headway in better understanding the role of genetics and genomics in medicine.
Applications of genomic information have led to:
- An increased knowledge of diseases like cancer and heart disease
- An increased knowledge of rare diseases like cystic fibrosis and Huntington’s disease
- Advancements in genetic testing technologies like DNA sequencing
- Advancements in new drug therapies that are targeted or tailored to an individual’s genetic information
Genetics vs. Genomics
However, before I get too far ahead of myself, let’s take a step back and define a couple of terms that many people find confusing and are often used interchangeably in health care; the terms are genetics and genomics.
Genetics is the study of how traits, conditions, and/or diseases are passed between generations in a family as well as the variation seen in the traits, conditions, and/or diseases due to single genes.
Genomics, however, is the study of all of a person’s genes (‘the genome’) and how different genes interact with each other and with an individual’s environment.
Application of Genomics in Health
Genomics and Cancer
I personally understand things better with an example, so let’s use cancer to further explain the difference between genetics and genomics. All cancer arises from harmful variations in our genes (called mutations) that we acquire spontaneously throughout our life from various things we are exposed to (alcohol, chemicals, smoke, etc.). It typically takes mutations in multiple genes to occur before a normal cell turns into a cancer cell. For this reason, all cancer is genetic in nature. Additionally, ~10% of people who develop cancer are born with a mutation in a gene that predisposes them to develop certain cancers; these are called hereditary cancer syndromes and common hereditary cancer syndromes include hereditary breast and ovarian cancer syndrome (BRCA1/2), Lynch syndrome and MUTYH-associated polyposis.
Due to advances in genomic medicine, we now have the ability to take cells from a cancer or tumor and test the genome of the cancer cells to see which genes are mutated. Based on this type of genomic testing, oncologists are able to recommend targeted therapies by prescribing chemotherapies that will take advantage of the specific mutations in the cancer. Individuals with metastatic colorectal cancer, for example, who are identified to have a mutation in the KRAS gene may respond to the drugs cetuximab (Erbitux) or panitumumab (Vectibix). However, if the colorectal cancer does not have a KRAS mutation, these drugs are unlikely to work in treating the cancer and are not likely to be used. Examples like this exist for many cancer types; Herceptin is used in breast cancers that have multiple copies of the HER2/neu fusion gene, tyrosine kinase inhibitors (Iressa or Tarceva) in lung cancers that have EGFR mutations and PARP inhibitors (Lynparza, Rubraca, Zejula) in ovarian cancers that have a BRCA1 or BRCA2 mutation.
Genomics and Heart Disease
Genome research has also had a significant impact on inherited heart diseases like long QT syndrome and Brugada syndrome that affect the electrical system of the heart (inherited arrhythmias), hypertrophic and dilated cardiomyopathy that cause enlarging of the heart and familial hypercholesterolemia that causes very high cholesterol. In 2003 we knew of 10-15 genes that could cause these hereditary conditions. Now we know of over 150 different genes that can cause these conditions. Additionally, we have learned that some genes can cause more than one type of inherited heart condition depending on the type of mutation or where the mutation occurs in a gene. Knowing this type of information allows physicians to develop tailored screening and treatment regimens to minimize the risk of experiencing a cardiac event.
Genomics and Preventive Healthcare
Genomic sequencing technologies have drastically improved over the years which has driven down the cost of genetic testing, making it more accessible to individuals. Because of this, many laboratories have started to offer genetic testing for ‘healthy’ individuals that want to know whether or not they have may have a risk of developing a genetic disease that the family history is not providing evidence of. As discussed above, this type of testing can be performed to assess whether someone has a high hereditary risk of developing cancer or heart disease. Individuals interested in starting a family can undergo carrier screening for a couple of hundred genetic diseases to determine whether they have a chance of having a child with a genetic condition. The idea behind proactive or healthy testing is to give people an advantage of knowing what health risks may impact themselves or their family members down the road so that increased screening can be initiated or started at a younger age to, ideally, detect the disorder at the earliest possible stage if it were to develop, or in some cases, prevent it altogether. Prevention can be done with medications, lifestyle modifications or surgery. It is important to appreciate that not everyone who has a risk of developing a genetic disease will go on to develop it. Your genetics are not your destiny!
Application of Genomics in Medicine
A newer application of genetics and genomics relates to something called pharmacogenomics. Pharmacogenomics is the study of how your genetic make-up determines how your body breaks down or metabolizes certain medications. Knowing this information can allow your doctors to ensure you are taking the right dose of a particular medication or, in some cases, recommend a different medication altogether if your genetic make-up indicates that you are likely to experience significant side effects or not respond to the medication. Pharmacogenomic testing can provide information about many medications, but not all medications have genetic information that can be used for prescribing purposes. The FDA recommends genetic testing before prescribing certain medications. For instance, codeine (narcotic) is a commonly used pain reliever, that is converted to morphine (a stronger narcotic) in the body. About 1-2% of the population metabolizes codeine too fast (called ultrarapid metabolizers). When this happens, too much morphine is produced which can lead to significant toxicity in the body. On the other hand, about 5-10% of the population metabolizes too slowly (called poor metabolizers); when this happens people do not get the pain relief that codeine is supposed to provide. Therefore, by doing a pharmacogenomic test, if someone is determined to be an ultrarapid or poor metabolizer of codeine, their physician can prescribe a different pain reliever to minimize the risk of side effects and maximize pain relief at the same time.
Future Role of Genetics and Genomics in Medicine
Genomic data has allowed medicine to advance by leaps and bounds, but there is still a lot we do not understand about the genome, especially as it relates to common diseases like diabetes, coronary artery disease, obesity, and autoimmune conditions. One emerging area as it relates to common disease and genomics are polygenic risk scores (PRS). PRS are genetic tests that look at hundreds to thousands of common and rare genetic variations in the genome linked to a specific disease. Through mathematical modeling based on the number of genetic variations identified as well as factoring in other risk factors, a PRS can determine whether you have a low, moderate or high risk of developing a disease. Given the level of risk, you and your physician may then be able to use this information to make diet and lifestyle modifications to minimize risk. However, as this test is so new, additional studies are needed to determine how accurate these tests are and whether having the information makes a difference in disease outcomes.
Further, it is believed that we will soon get to a point where at the time of birth, every baby has their whole genome sequenced so that disease risks can be assessed early in life. Can you imagine the possibilities?
