Genetic Testing and Huntington’s Disease
|Alicia was a consultant for Lisa Genova’s book
“Inside the O’Briens,” which is about Huntington’s
disease. (Image via Simon & Schuster)
As a genetic counselor specializing in research on Huntington’s disease, I have met numerous patients with the disease and families who are impacted by it. Huntington’s disease is an inherited brain disorder that is caused when specific cells in the brain die. Symptoms include involuntary movements, cognitive decline and mood disturbances. They typically start in middle age and become worse as the disease progresses until death occurs. Currently, there is no cure for the disease.
It’s estimated that for every person who has Huntington’s disease, the disorder impacts another 20 individuals including friends, caregivers and family members, many of whom are at-risk for developing it themselves.
What Causes Huntington's Disease?
Everyone has the Huntington’s disease gene but only those who have a genetic mutation in the gene may develop the disease. The mutation involves an increase in a small segment of DNA, called a CAG repeat. Individuals who have 36 CAG repeats or more are considered mutation-positive and will develop Huntington disease in their lifetime. Those with 26 CAG repeats or fewer are mutation-negative and will never develop the disease. Some individuals fall in the middle and have what is called an intermediate allele (27 to 35 CAG repeats), meaning they will usually not develop the disease but there may be a chance their children will.
A “Family Disease”
Huntington’s disease is often described as a family disease. Children whose parents are mutation-positive have a 50 percent chance of developing the disease when they are adults. Children of parents who are mutation-negative are not at risk.
Adults who have a family member with Huntington’s disease but do not yet have symptoms of the disease can determine if they have the genetic mutation by undergoing predictive genetic testing with a simple blood test. A neurological exam is also performed to look for early symptoms.
I recommend that anyone considering predictive testing meet with a genetic counselor.
The Role of Genetic Counseling
The decision whether to have predictive testing for Huntington’s disease is extremely personal, and it’s important to take your time and make an informed choice. A genetic counselor can help you talk through all the factors to consider.
During the genetic counseling sessions you’ll discuss many issues, including the potential benefits and harms of testing, your motivations for testing, your expectations about the test result, the impact either a mutation-positive or negative result might have on your life, and strategies for dealing with the test result. A genetic counselor will also help you identify other issues, such as the impact testing may have on your relationship with your spouse, children and extended family members, your career, and your insurance and finances. For example, results from predictive testing could make it difficult to purchase life, disability or long-term care insurance.
Emotional Impact of Testing
The emotional impact of receiving predictive test results can be difficult to anticipate.
"The decision whether to have predictive testing for Huntington’s disease is extremely personal, and it’s important to take your time and make an informed choice."
Individuals who receive a mutation-positive result may initially experience feelings of depression, anger, fear or despair. Many people struggle with not knowing when the first symptoms will appear, and may start to “symptom watch” and wonder if occasional clumsiness or forgetfulness are early signs of the disease. With time and support, most people come to accept their result.
Individuals who receive a mutation-negative result may initially experience feelings of joy and relief. But some struggle with “survivor’s guilt” because they escaped the disease while other family members did not. They may also feel an increased responsibility to care for affected family members. It’s important to acknowledge that individuals who receive a negative result may also benefit from additional support following testing.
Find a Genetic Counselor
If you would like more information on Huntington’s disease, visit the Huntington’s Disease Society of America’s website at hdsa.org. If you’d like to speak to a genetic counselor, you can locate one in your area using NSGC’s “Find a Genetic Counselor” tool.
Alicia Semaka, PhD, CGC, CCGC, is a Huntington’s disease researcher and postdoctoral fellow at the University of British Columbia. She also served as a consultant for Lisa Genova’s (“Still Alice”) latest book “Inside the O’Briens” about Huntington’s disease.