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Huntington's Disease (HD) is a rare degenerative brain disorder that can cause serious and debilitating mental and physical changes. The slow-progressing disease is an inherited disorder, caused by a defective gene. Usually symptoms began to appear when affected individuals reach middle age. Huntington's is one of the most devastating diseases to deal with. As the disease advances, neurons in the brain die - causing sufferers to experience slurred speech, jerky uncontrollable movements, anxiety, depression, impairments in cognitive ability, memory loss, seizures, sleep disturbances and a number of other possible symptoms.
Although research into HD is making progress; as of yet, no cure exists and there is no way to stop its progression. The disease impacts not only the individual sufferer, but the entire family unit. The affected individual is likely to require extensive care, supervision and financial assistance in the later stages of the disease.
According to the Family Caregiver Alliance, 200,000 Americans carry the risk of inheriting the disease from a parent that is affected. In the 30,000 Americans that have already been diagnosed there is a 50 percent risk that they will pass the mutated gene responsible for Huntington's onto their children. By accessing a Huntington's disease test, individuals can find out if they have developed, or will develop HD.
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Huntington's Genetic Testing
A direct gene test called a presymptomatic test is usually done for those at risk of contacting HD. Using a blood sample the test analyzes DNA (deoxyribonucleic acid). A DNA sample from a parent or other close relative suffering from the illness may also be needed.
The Huntington's gene, resides on chromosome 4. Within this segment of DNA, nucleotides repeat in patterns of three called a trinucleotide. The trinucleotide involved in HD is cytosine-adenine-guanine (CAG). The number of times a CAG pattern repeats determines the risk of developing HD. A negative test result indicates that an individual is showing less than 30 CAG repeats, a normal amount. Those with 40 or more repeats have a high risk of contacting HD. Some individuals will fall into a gray area, having a range of CAG repeats between 30 and 40. They will not develop HD but their children may have a higher risk.
Though a difficult decision to make, prenatal testing can be done on an unborn fetus to test for HD. In amniocentesis, otherwise known as an amniotic fluid test, amniotic fluid is extracted from the amniotic sac of the developing fetus and submitted for testing. Genetic material from chorionic villus cells found within the placenta can also be tested. Called a chorionic villus sampling (CVS), this test can be done earlier in the pregnancy than amniocentesis. Parents may use prenatal testing to decide to terminate a pregnancy when testing indicates a high risk of carrying the mutated gene.
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Huntington's Diagnostic Testing
When a neurologist suspects an individual is already exhibiting symptoms of HD, a confirmatory test can be done. A careful review of family history of the disease and an extensive patient history is generally the first step. A range of investigative procedures will then be done to identify the disease starting with a CT (computerised tomography) scan of the brain. The CT creates a computer-generated image of the brain structure; neurologists can use this test to look for structural changes. Individuals suffering from Huntington's will typically show shrinkage in the caudate nuclei and putamen.
Tests will also be done to check hearing, eye movement, strength, coordination, reflexes and balance. Other laboratory, neurological and brain imaging tests may also be needed. For confirmation a genetic test can be done.
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The Merits of Testing
Genetic testing is not for everyone. Some individuals would prefer not to known if they have the mutated gene since no lifestyle changes or medication can stop the progression of HD. The psychological effects of living with the knowledge that one day, symptoms of the disease will begin to appear can also be severe. According to the Huntington's Disease Society of America genetic testing may be free at some research institutes and could be as much as $1500 at other centers. Though health insurance may cover the cost of presymptomatic testing, genetic discrimination could occur.
Those with a strong family history of the disease however, can benefit from foreknowledge. A positive test can encourage individuals to make important decisions about their future. Helping them to make career decisions and decide on the consequences of getting married and having children. It can also help these individuals develop a contingency plan – deciding issues related to home based and long term care.
For those who ultimately decide to undergo a Huntington's disease test the International Huntington Association recommends that these individuals choose a HD predictive testing center. These centers do more than just administer a blood test. A multidisciplinary team is assembled and patients receive genetic counseling, psychological counseling, neurological exams, explanation of the test results and post-test counseling. These laboratories are held to high standards in the results they provide and in determining the medical ethics of genetic testing.
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Family Caregiver Alliance (http://www.caregiver.org/caregiver/jsp/content_node.jsp?nodeid=574)
Huntington's Disease Society of America (http://www.lkwdpl.org/hdsa/hdtest.htm)
International Huntington Association (http://www.huntington-assoc.com/)
National Human Genome Research Institute (http://www.genome.gov/10001215)
DNA Double Helix. (Photo by National Human Genome Research Institute; http://www.genome.gov/pressDisplay.cfm?photoID=96)
Human Chromosomes. (Photo by Jane Ades, National Human Genome Research Institute; http://www.genome.gov/pressDisplay.cfm?photoID=98)