The expanding field of genetics and growing research linking mutations in specific genes to increased risk of cancer (cancer susceptibility genes) have rapidly expanded the field of predictive genetic testing. Predictive genetic testing may help identify people who are at an increased risk for developing certain types of cancer, but also carries many limitations and risks. People need to fully understand the process and its implications.
A gene is a hereditary unit of DNA that occupies a specific location on a chromosome. Genes carry directions to cells and tell them to make specific proteins that perform and regulate all body functions. Genes are capable of replicating themselves at each cell division. A mutation is a change in the usual DNA sequence of a particular gene. Mutations can be beneficial, harmful, or neutral. Many diseases, including cancer, begin in the genes. The genetic mutation that causes cancer can be inherited from a parent or it can be a random mutation that occurs as a result of a mistake during cell division or in response to environmental factors.
Current research suggests that only 5-10% of cancers are inherited. This hereditary influence begins with the genes that are passed from parent to child. Genes come in pairs, with one copy inherited from each parent. Parents can pass on a normal copy or, if they have one, an abnormal or mutated copy of a gene. Determining the probability of inheriting a gene mutation and/or of developing cancer as a result of a gene mutation is a complicated process that requires an understanding of heredity, genetics and the role of genes.
Germline testing be considered for all patients with ovary, breast, prostate, pancreatic, and lung cancer
Germline genetic testing evaluates an individual for inherited mutations (otherwise known as pathogenic or likely pathogenic variants) that can be responsible for the development of cancer.
What are germline mutations?
Germline mutations are found in virtually all cells of the body because they originate from the fundamental DNA that an individual inherits from their parents. Germline mutations are present in the DNA of a parent’s reproductive cells (egg or sperm). These mutations change the genetic material that the child receives from their parent (hereditary). You can inherit germline mutations from either parent and they are present at birth.
What are somatic mutations?
Somatic mutations are a change to a person’s DNA that occurs after conception and can occur in any cell in the body. Somatic mutations are not inherited and happen sporadically or randomly, without the mutation existing in a person’s family history. Somatic mutations can’t be passed on to future generations.
How do somatic and germline mutations affect the body?
Most mutations don’t cause problems for us, but some mutations create symptoms of disease. Genetic conditions are disorders that are caused by changes to your genome. Your genome is made up of your DNA, genes, and chromosomes.
What is DNA?
DNA exists in every cell in the human body and holds the genetic code which is your body’s instruction manual. DNA is a structure made up of four bases:
- Adenine (A)
- Cytosine (C)
- Thymine (T)
- Guanine (G)
Understanding DNA Damage Response or DDR and Cancer Treatment
What is DNA Damage Response or DDR?
The bases form pairs (base pairs): A with T and C with G. The base pairs connect with a sugar molecule and a phosphate molecule (to form a nucleotide). As the nucleotides form, they make a shape that looks like a spiral staircase (double helix) in your cells. The base pairs are the steps, and the sugar and phosphate molecules are the handrails.
What is a Pathogenic Germline Variant (PGV)?
A PGV is a germline mutation that can lead to cancer or other diseases. PGV’s can cause cancer in breast, colon, lung, prostate and all cancer cell types.
- Identification of pathogenic germline variants through testing has important implications for patients and their families.
- Up to 15% of patients with cancer have pathogenic germline variants, nearly all of which could be clinically actionable.
- Variants often occurred in DNA damage-repair/homologous recombination-repair (DDR/HRR) genes.
Moreover, most patients with pathogenic germline variants, or PGVs, had them in DNA Repair Genes including BRCA1 and BRCA2, making them potentially eligible for targeted treatment on a clinical trial. Genes in which PGVs occurred most often include BRCA1-2, CHEK2, ATM, TP53, EGFR, APC, and PALB2 (0.5%).
Top 5 Things to Know about DNA Testing
Your family history offers clues.
A thorough grasp of your family history can offer clues about the kind of testing that may benefit you. Encourage discussions about health history among your relatives—both male and female—to help determine if health problems such as breast cancer run in the family. If they do, genetic counseling and testing may provide a better understanding of the risks to you and your family members and what to do about them. As you gather clues, notice if there are patterns of cancer, heart disease, or other illnesses that run through the generations. Recognizing inherited patterns of disease can help the entire family. It is important to look at the health history on both sides of the family. For example, when it comes to hereditary breast cancer, your father’s side of the family is equally important. Most women don’t realize that they can inherit the breast cancer gene from their father.
You can use results to plan ahead.
There are a number of key times in life when genetic testing can help you plan ahead, such as if you want to have a baby or are concerned about hereditary cancers. In the case of pregnancy screening, a carrier screen performed on a sample of blood or saliva from both you and your partner can provide useful insights prior to conceiving. More than 100 rare but significant genetic diseases can be included in a carrier screen, such as cystic fibrosis, spinal muscular atrophy, Hurler syndrome, and Wilson’s disease. Some of the diseases on carrier screening panels can be improved with such early interventions as nutritional changes at birth or lining up the right medical specialists. With respect to hereditary cancers, understanding your risk ahead of time allows you to take advantage of frequent surveillance or consider risk-reducing medications, lifestyle changes, or even prophylactic surgery.
Carriers of genetic diseases are often healthy.
A carrier of a genetic disease is typically a healthy individual. Depending on the type of disease involved, a carrier can remain healthy but pass the disease risk to future generations, as with cystic fibrosis and spinal muscular atrophy. In the case of certain cancers, like hereditary colon cancer, a carrier is more prone to developing a cancer early in life as well as passing on the propensity. Many of us are carriers of rare diseases and do not know until we are tested. This is especially the case with recessive diseases, which can appear to skip generations. For a recessive disease to manifest, both mom and dad must be carriers of the same rare gene. Sometimes people choose not to pursue carrier screening because they have no concerning family history, but it’s important to note that more than 80 percent of children with genetic diseases are born to parents with no prior history in their families.
Genetic counselors can help you navigate the results.
Genetic counselors are experts in facilitating decision-making around DNA testing. They understand that each person has his or her own set of values, life goals, and experiences that define what it means to be fully informed and empowered. The decision to have genetic screening involves many factors. It is helpful to talk about the pros and cons with a genetic counselor and determine whether a screening test is right for you. Questions that may arise in a session include why you want the information, what you plan to do with the results, and how to talk to family members about the implications. If you are unable to visit a genetic counselor in person, some laboratories offer free telephone access to board-certified genetic counselors. With good counseling, you will feel empowered to understand your results and make informed health choices that are right for you.
It’s surprisingly affordable and often covered by medical insurance.
Just a few years ago, testing for one genetic disease (think cystic fibrosis or sickle cell disease) could cost a few hundred dollars. Advances in DNA technologies have helped reduce the cost of genetic testing so that today, for that same price or less, laboratories are offering DNA tests for large panels of genetic diseases. What’s more, many insurance plans understand the value of genetic testing in preventing the onset of disease and offer coverage for qualifying individuals.
If you are interested in learning more, talk with your doctor and start the conversation with your family. After all, you share a lot more with your family than you think.