Approximately 200,000 people in the United States are at risk for Huntington disease because they have a parent with the condition. If you are among those at risk, you know that family planning is a complicated prospect. People with Huntington disease, or at risk for Huntington disease, who are considering becoming parents should discuss with their doctor how their disease may progress while they are a parent. Also, they may consider using IVF with PGT for Huntington disease so they do not pass on the familial mutation to their children.
What Is Huntington Disease?
Huntington disease is caused by a mutation in a single gene that you inherit from a parent with the disease. Your genes consist of DNA — your unique genetic material — found in almost every cell in your body. DNA is like a personal barcode. This code is made up of a unique combination of four chemicals: adenine (A), guanine (G), cytosine (C) and thymine (T). These chemicals pair up with each other — A with T and C with G — to form what’s called a base pair.
Huntington disease is caused by a mutation in the HTT gene called a trinucleotide expansion, which triggers the production of a protein called huntingtin that is involved with nerve cells in the brain. The HTT gene contains a segment in which cytosine, adenine, and guanine (CAG) repeat multiple times. In a normal HTT gene, CAG repeats 10 to 35 times. In people who have Huntington disease, the segment repeats from 36 to 120 times or more. People who have 36 to 39 repeats could one day develop symptoms of Huntington disease. People with 40 or more repeats almost always develop the condition.
Those with Huntington disease have a 50 percent chance of passing the mutation on to their children, which may concern prospective parents. In vitro fertilization (IVF) with preimplantation genetic testing (PGT) for Huntington disease dramatically reduces the risk of having a child with the Huntington mutation.
Facing Difficult Questions
When starting a family, people at risk for Huntington disease have multiple factors to consider. “You might also be thinking about whether you want to be a parent with Huntington disease,” says Robin Bennett, a certified genetic counselor and co-director of the Genetic Medicine Clinic at the University of Washington Medical Center. Symptoms of the condition, which include problems with coordination, behavior and personality changes, and declining thinking skills, can arise when you are in your 30s or 40s.
“Your perception of what the condition will mean for you very much depends on your experience with the parent who has the condition,” says Bennett.
Weighing the Options
Prospective parents at risk for Huntington disease can choose to conceive naturally, in which case they may decide to test the fetus for genetic abnormalities through amniocentesis or chorionic villus sampling during the pregnancy, and then decide whether to continue with the pregnancy based on the results.
Some prospective parents choose to use donor sperm or donor eggs.
Another option is to conceive via IVF with PGT. With this method, the conception of an embryo takes place in a laboratory outside the body. Before an embryo is transferred to the uterus, it undergoes PGT for the Huntington gene mutation. Only an unaffected embryo or embryos will be implanted.
How PGT for Huntington Disease Works
With PGT for Huntington disease, clinicians take five to 10 cells from an embryo biopsy and test it for the mutation. If there is an embryo that does not have the Huntington mutation, it will be implanted in the mother. Additional unaffected embryos can be frozen to be used if the prospective parents desire additional children. Numerous individuals and couples have utilized PGT to have children that have not inherited the disease.
Prospective parents should understand that IVF with PGT doesn’t always result in pregnancy on the first cycle. In some cases, all embryos have the disease-causing gene variant or another issue that makes them unsuitable for implantation. Also, while PGT is 98% accurate, it is recommended that parents confirm a negative diagnosis with prenatal testing.
Although not every implantation results in pregnancy, many do. “It’s a common option that people take,” says Bennett. “Huntington is certainly one of the most common reasons people I work with decide to do PGT.”