Living at Risk
Genetic Testing
HD is a disease of families. Though everyone is born with the huntingtin gene, the disease is caused by an abnormal copy of the gene that is passed from parent to child. It is not contagious in any way. Only a person who is born with the abnormal gene can ever get the illness or pass it on to their children. Every person who carries the abnormal copy of the gene will eventually develop symptoms, if they live long enough.
Every child born to an affected parent has a 50% chance of being born with the gene that causes the disease. Males and females have the same chance of inheriting the abnormal gene. Those who have not inherited the gene will not get the disease and they cannot pass it on to their children. HD does not "skip" generations.
Soon after the HD gene was identified in 1993, a direct gene test was developed which allows a person to find out if they carry the abnormal HD gene and will someday develop the disease. While the test is very accurate, it cannot determine when the symptoms of the disease will begin or how severe the symptoms will be. People without symptoms of HD who test positive for the gene may remain unaffected for many years.
Genetic testing for HD presents people at risk for the disease with a difficult choice, given the current absence of an effective treatment or cure. Many people see no benefit in knowing that they will someday develop the disease. Others want an end to uncertainty so that they can make informed choices about the future. The decision whether to test or not is intensely personal and there is no "right" answer.
The Huntington's Disease Society of America recommends that at risk individuals who are considering genetic testing do so at a genetic testing center that follows HDSA guidelines for genetic testing. A complete list of the centers can be found here. Testing procedures at these centers involves sessions with professionals who are knowledgeable about HD and generally include one session devoted to each of the following: genetic counseling, a neurological exam, a psychological interview, discussion of the results and follow up. The genetic test itself takes several weeks and is performed on a blood sample.
Genetic testing for children is typically prohibited before age 18, as the child may not understand the full implications of testing and may be vulnerable to pressure from others. However, a child under the age of 18 may be tested to confirm a diagnosis of juvenile onset HD after a thorough neurological exam.
For couples planning a family, prenatal testing of an at-risk fetus is an option. This can be done through a direct genetic test or through a "nondisclosing" variation of the test that approximates the risk that the fetus is carrying the HD gene without disclosing the genetic status of the at-risk parent. A second option is PGD or pre-genetic diagnostic testing in which eggs that have been fertilized are tested for the abnormal HD gene within a few days of fertilization and only those without the mutated gene are re-implanted in the mother. This procedure is also a non-disclosing option as only those blastocysts that are gene negative are used. Other options include amniocentesis to identify fetuses that carry the mutated gene for possible termination, and adoption. Couples planning a family should consult with a genetic counselor in order to explore the option that may be right for them.
Genetic Counseling/Testing Centers