With genetic testing becoming easier, less expensive, and more widely accepted, a growing number of people are undergoing screening in order to determine their risk for developing certain diseases, as well as to identify and diagnose the underlying causes of particular symptoms that they are already experiencing. Using DNA samples—typically from blood tests or inner cheek swabs—these tests look for particular genetic mutations, known as “genetic markers,” which have been associated with certain health conditions. Read on to learn more about how genetic testing might be used to gauge your risk of developing five common diseases.
1. Breast and ovarian cancer
Genetic testing for breast cancer captured the public’s attention in 2013, when actress Angelina Jolie announced that she had undergone a preventive double mastectomy after a genetic test for mutations in the BRCA1 and BRCA2 genes estimated that she had a 65% chance of developing the disease. As the National Cancer Institute explains, the BRCA genes fall into the class of “tumor suppressors.” However, when mutations occur in these genes, uncontrolled cell growth can follow. The chances that women with BRCA mutations will develop breast cancer is five times higher than for those without these mutations. Likewise, their chance of developing ovarian cancer is between 15 and 40 times greater. However, it is important to keep in mind that only about 5% to 10% of annual breast cancer diagnoses involve BRCA mutations. The vast majority of the 200,000 cases of breast cancer diagnosed in the US every year occur in women with no known family history of the condition.
2. Celiac disease
About 2 million Americans are affected by this autoimmune condition in which the protein gluten, which is most commonly found in wheat, triggers an immune system reaction that attacks the small intestine, causing symptoms such as diarrhea and abdominal pain. However, many with the condition have experienced difficulty in obtaining a diagnosis for their condition: some have no easily discernable symptoms, while others have their symptoms mistaken for conditions such as irritable bowel syndrome. Genetic testing has helped to correct this confusion and provide an accurate diagnosis. Since celiac disease is up to 87% attributable to genetics, according to the genetic testing company 23andMe, tests can identify the condition by looking for specific versions of genes that produce the immune system protein HLA-DQ. In terms of one’s likelihood of developing the condition, scientists estimate that roughly 1 in 22 people will develop celiac disease if a parent, child, or sibling also has it (a second-degree relative such as an aunt or grandparent lowers the risk to 1 in 39).
3. Age-related macular degeneration (AMD)
For Americans over the age of 60, AMD is the leading cause of vision loss and eventual blindness. In people with this condition, the retinal tissue in the back of the eye deteriorates, impairing the eye’s ability to transmit images to the brain and leading to the loss of central vision, which is crucial for activities such as reading or driving. Although environmental factors can play a role, the development of AMD is attributed to heredity in up to 71% of cases, with people who have siblings with AMD being three to six times more likely to develop the condition as compared with the general population. Genetic tests that screen for AMD focus on a genetic group known as ABCR genes. Variations in these genes can indicate a 30% greater chance of developing AMD.
Long considered to be due entirely to environmental factors, obesity is increasingly seen today as a complex condition that owes its development to a number of different influences, some of them genetic. As of yet, no clinical research has conclusively demonstrated how many genes might be involved in the development of obesity, but companies such as 23andMe attribute obesity to hereditary factors in as many as 84% of cases. Specifically, variations occurring in a gene called FTO have been found to account for a weight difference of nearly 7 pounds. Similarly, FTO gene levels are found to be higher in fatty tissue and to have virtually no association with muscle mass, bone density, or other traits beyond fat tissue.
5. Parkinson’s disease
Affecting at least 500,000 Americans, with another 50,000 cases diagnosed each year, Parkinson’s disease (PD) stands to benefit from recent progress in the sphere of genetic testing and treatment. A neurological disorder caused when dopamine-producing brain cells begin to deteriorate, PD’s most common symptoms include trembling in the limbs, face, and jaw, as well as slowed movement and difficulty with coordination. Although the average lifetime risk of developing PD—a condition that mostly affects people over the age of 50—is only 1% to 2%, recent studies have linked a much higher risk level with mutations in the LRRK2 gene. Of the more than 50 variations of this gene in existence, several have been strongly associated with PD. The G2019S mutation, for example, can signal a 28% chance of developing PD before the age of 59 and a 74% chance of developing the condition before age 79.