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Frequently Asked Questions
Many questions are common to the HD community. Some of the most frequently asked questions are answered below. For more detailed information, please see HD Description on this website. You may also want to read 10 The Most Commonly Asked Questions which will take you to the Juvenile HD website.
What are the symptoms of HD?
Three domains are commonly affected: cognitive (thinking), motor and behavior. The symptoms and progression of the disease vary from person to person; even members of the same family may have different symptoms. Some individuals can have mild involuntary movements (chorea) and have more of theemotional/behavioral symptoms or vice versa. The symptoms of HD usually appear during the late 30's to mid-40's, but sometimes children or the elderly can have symptoms.
difficulties with: speech, swallowing, balance, walking
What causes the symptoms of HD?
HD results from the degeneration of brain cells (neurons) in certain specific areas of the brain. This deterioration is genetically programmed. Structures deep within the brain, called the basal ganglia, are affected. The basal ganglia are responsible for a number of important functions, including coordinating movement. The outer part of the brain, which is crucial to thought, perception, and memory is also
affected. The result is the uncontrolled movements and emotional disturbance that are characteristic of HD.
Is there treatment for HD?
There is no cure, but current medications enable a much better quality of life for those with HD. Doctors may prescribe a number of medications to help control the emotional and movement problems associated with HD. It is important to remember how-ever, that while medicines may help keep these clinical symptoms
under control, there is no treatment to stop or reverse the course of the disease.
Most drugs used to treat the symptoms of HD have side effects such as fatigue, restlessness, or hyperexcitability. Sometimes, it may be difficult to determine if a particular symptom, such as apathy or incontinence, is a sign of the disease or a reaction to medication.
The current Physician's Guide To HD (to The Management of Huntington's Disease), 2nd Edition, details helpful treatments and medications that are available now. The book is available from the Huntington's Disease Society of America (HDSA).
How common is HD?
In the U.S., the overall prevalence of HD is about 1 in every 10,000 persons. At least 150,000 more people in the U.S. are at 50-50 risk for developing HD. However, with more accurate diagnosis and more open discussion about HD, the actual occurance is believed to be much higher.
How is HD inherited?
HD is a familial disease that appears to be passed "from generation unto generation," from parent to child. Each child of a parent with HD has a 50/50 chance of having HD. However, in reality, the disease itself is not transmitted, but rather a "mutation" (a change in a gene). The gene that produces HD lies on chromosome number 4.
In 1983, the HD gene was first localized near the tip of the short arm of chromosome 4, but the HD gene itself was not isolated for another decade. (The short arm of a chromosome is symbolized by the letter "p" standing for petit, small in French.) In 1993, the gene was finally isolated to a small segment of chromosome 4 (band 4p16.3).
HD is a dominant disorder since only one copy of the Huntington gene, inherited from one parent, is necessary to produce the disease.
Can HD occur without a family history of HD?
Yes, rarely. A small number of cases of HD are sporadic, that is, they occur even though there is no family history of the disorder. These cases are thought to be caused by a new genetic mutation - an alteration in the gene that occurs during sperm development.
What is Juvenile HD (JHD)?
The terms early-onset HD or juvenile HD are often used to describe HD that appears in a young person. Some of those afflicted develop symptoms of HD when they are very young - before age 20. Symptoms can include subtle changes in handwriting and slight problems with movement, such as slowness, rigidity, tremor, and rapid muscular twitching, called myoclonus. Several of these
symptoms are similar to those seen in Parkinson's disease, and they differ from the chorea seen in victims who develop the disease as adults. (Note: see Juvenile HD Website)
People with juvenile HD may also have seizures and mental disabilities. The disease progresses most rapidly in individuals with juvenile or early-onset HD, and death often follows within 10 years.
Can testing be done for HD before symptoms appear?
Discovery of the HD gene has led to an accurate blood test that is applicable to the majority of people at risk for HD. The genetic testing itself involves donating a small sample of blood that is screened in the laboratory for the presence or absence of the HD gene mutation. Results of the test should be given only in person and only to the individual being tested. Test results are confidential.
Regardless of test results, follow-up visits are recommended.
In order to protect the interests of minors, including confidentiality, testing is not recommended for those under the age of 18 unless there is a compelling medical reason (for example, the child is exhibiting symptoms).
In terms of emotional and practical consequences, not only for the individual taking the test but for his or her entire family, testing is enormously complex and has been surrounded by considerable controversy. For example, people with a positive test result may risk losing health and life insurance, suffer loss of employment, and other liabilities. Persons undergoing testing may wish to cover the cost themselves, since coverage by an insurer may lead to loss of health insurance in the event of a positive result, although thismay change in the future.
With the participation of health professionals and people from families with HD, scientists have developed testing guidelines. All individuals seeking a genetic test should obtain a copy of these guidelines. HDSA has information on sites that perform testing using the established procedures and they strongly recommend that individuals avoid testing that does not adhere to these guidelines.
Can testing before birth
(prenatal testing) be done for HD?
Testing of a fetus (prenatal testing) presents special challenges and risks and some centers do not perform genetic testing on fetuses. Because a positive test result using direct genetic testing means the at-risk parent is also a gene carrier, at-risk individuals who are considering a pregnancy are advised to seek genetic counseling prior to conception.
Some at-risk parents may wish to know the risk to their fetus but not their own. In this situation, parents may opt for prenatal testing using linked DNA markers rather than direct gene testing. In this case, testing does not look for the HD gene itself but instead indicates whether or not the fetus has inherited a chromosome 4 from the affected grandparent or from the unaffected grandparent on the side of the family with HD.
If the test shows that the fetus has inherited a chromosome 4 from the affected grandparent, the parents then learn that the fetus's risk is the same as the parent (50-50), but they learn nothing new about the parent's risk. If the test shows that the fetus has inherited a chromosome 4 from the unaffected grandparent, the risk to the fetus is very low (less than 1%) in most cases.
Another option available to parents is in vitro fertilization (IVF) with Preimplantation screening. In this procedure, embryos are screened to determine which ones carry the HD mutation. Embryos determined not to have the HD gene mutation are then implanted in the woman's uterus.
How does someone decide whether to be tested?
The anxiety that comes from living with a 50 percent risk for HD can be overwhelming. Some individuals choose to undergo the test out of a desire for greater certainty about their genetic status. They believe the test will enable them to make more informed decisions about the future. Others choose not to take the test. They are at peace with being at risk and with all that may entail. There is no
ight or wrong decision, as each choice is highly individual.
Whatever the results of genetic testing, the at-risk individual and family members can expect powerful and complex emotional responses. The health and happiness of spouses, brothers and sisters, children, parents, and grandparents are affected by a positive test result, as are an individual's friends, work associates, neighbors, and others. Because receiving test results may prove to be devastating, testing guidelines call for continued counseling even after the test is complete and the results are known.
How is Huntington's disease diagnosed?
The most direct test for HD is a genetic test: analysis of DNA derived from a blood sample, to determine how many CAG repeats are present in the Huntington gene.
The presence of 40 or more CAG repeats means that a patient will develop HD. A patient will not develop HD if 28 or fewer repeats are present.
Tools used to determine whether an individual at risk for HD has begun to develop the disease, and/or to rule out other possible diagnoses, include:
The neurological exam includes tests of:
- Eye movement
- Mental status