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This article is, in part, based on information from the National Institutes of Health (NIH) and the National Center for Biotechnology Information (NCBI).
What is Huntington disease?
Huntington disease (HD) is an inherited disorder caused by the degeneration of certain nerve cells in the brain. HD causes involuntary movements (chorea) and loss of intellectual abilities. The condition begins most often in mid-adulthood and progresses slowly to death. The identification of the gene for HD now makes it possible to determine who will develop this disease by examining their DNA from a blood sample in the laboratory.
The most commonly used names for the disorder are Huntington disease and Huntington's disease. Other names in usage include Huntington chorea and Huntington's chorea.
The disorder is named after a little-known American family doctor by the name of George S. Huntington (1850-1916) who wrote about an illness he saw as "an heirloom from generations away back in the dim past." The illness was inherited and caused a movement disorder called chorea.
What is chorea?
HD has been known at least since the Middle Ages. One of the earliest names for it was "chorea," the Greek word for dance (as in "choreography"). "Chorea" refers to a particularly striking feature of Huntington disease: the tendency to writhe, twist, and turn in a constant, uncontrollable motion - like a dance.
Later, other descriptive names were devised for the disorder. The name "hereditary chorea" emphasizes how the "dancing disease" was passed from parent to child. The terms "chronic progressive chorea" and "degenerative chorea" both stress how the signs and symptoms of the disease worsen with time.
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 basalganglia, 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, loss of intellectual faculties, and emotional disturbance that are characteristic of HD.
How common is HD?
The frequency of HD depends on the particular population. In the U.S., the overall prevalence of HD is about 1 in every 10,000 persons. Approximately 45,00 people in the U.S. now have HD. At least 150,000 more people in the U.S. are at 50-50 risk for developing HD.
The frequency of HD in Finland is 5 cases per million as contrasted with
frequencies of 30 to 70 per million in most Western countries. Almost all of the cases in Finland have been determined to have originated from a single source. It appears that the HD gene arrived in Finland by way of foreign immigrants.
The largest concentration of HD in the world is in the Lake Maracaibo area of Venezuela where one huge family has produced many cases of HD. This family provided the crucial blood samples used to locate and define the HD gene.
How Is HD Inherited?
HD is a familial disease that appears to be passed "from generation unto generation," from parent to child. 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).
The impact of a gene depends partly on whether it is dominant or recessive. If a gene acts in a dominant manner, then only one copy of the gene, from either parent, is required to produce the disease. If the gene is recessive, both parents must provide a copy of the gene for the characteristics to be present in the offspring.
HD is a dominant disorder since only one copy of the Huntington gene, inherited from one parent, is necessary to produce the disease.
What is wrong with
the Huntington gene?
The genetic defect that is responsible for HD involves a tiny sequence of DNA on chromosome 4. Several of the genetic code words (base pairs) in the DNA are redundantly repeated many, many times.
The HD gene encodes a protein. This protein has been named huntingtin. (The name may be confusing but that is what it is called). The function huntingtin is as yet unknown. The redundantly repeated sequence in the gene code causes an abnormal form of huntingtin to be made.
It is the presence of this abnormal form of huntingtin protein that causes the harm in HD. How the abnormal huntingtin leads to Huntington disease is still incompletely understood.
Can HD worsen from one
generation to the next?
Yes. The abnormal HD gene is unstable and can change from generation to generation. This explains why some persons have an earlier onset or more severe disease than their ancestors.
Does everyone with the Huntington
gene develop the disease?
If they live long enough, yes. Each person who inherits the HD gene and lives long enough sooner or later develops the disease. However, the time of onset of the disease can vary greatly from one person to the next.
Therefore, an individual with the gene who may have developed HD at an advanced age may die of a completely different cause well before exhibiting any signs.
Are the children in all HD
families at equal risk?
No. In some families, all the children may inherit the HD gene; in others, none do. Whether one child inherits the gene has no bearing on whether others will or will not. (Each child has a 50% chance of NOT inheriting the disease as well as inheriting it.)
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 are the major signs and
symptoms of Huntington disease?
The early signs of the disease vary greatly from person to person. In general, the earlier the symptoms appear, the faster the disease progresses.
Family members may first notice that the individual experiences mood swings or becomes uncharacteristically irritable, apathetic, passive, depressed, or angry. These symptoms may lessen as the disease progresses or, in some victims, may continue and include hostile outbursts or deep bouts of depression.
HD may affect the sufferer's judgment, memory, and other cognitive functions. Early signs might include having trouble driving, learning new things, remembering a fact, answering a question, or making a decision. Some may
even display changes in handwriting. As the disease progresses, concentration on intellectual tasks becomes increasingly difficult.
In some individuals, the disease may begin with uncontrolled movements in the fingers, feet, face, or trunk. These movements-- which are signs of chorea -- often intensify when the person is anxious. HD can also begin with mild clumsiness or problems with balance. Other persons develop the movements of chorea later on as the disease progresses. They may stumble or appear uncoordinated. Chorea often creates serious problems with walking, increasing the likelihood of falls.
The disease can progress to the point where speech is slurred and vital functions, such as swallowing, eating, speaking, and especially walking, continue to decline. Some sufferers are unable to recognize others. Many, however, remain aware of their environment and are able to express emotions.
At what age does HD appear?
The age of the onset of the signs and symptoms of HD as well as the rate of disease progression can vary greatly. Adult-onset or classic HD, with its disabling, uncontrolled movements, most often begins during middle age.
What is rigid HD?
Some persons develop Huntington disease as adults, but without the chorea. They may appear rigid and move very little, or not at all, a condition called "akinesia." These individuals are said to have akinetic-rigid HD or the Westphal variant of HD.
What is juvenile HD?
Some of those afflicted develop symptoms of HD when they are very young - before age 20. The terms early-onset HD or juvenile HD are often used to describe HD that appears in a young person.
A common sign of HD in a juvenile is a rapid decline in school performance. Symptoms can also 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. People with juvenile HD may also have seizures and mental disabilities.
As mentioned previously, the earlier the onset of HD, the faster the disease seems to progress. The disease progresses most rapidly in individuals with juvenile or early-onset HD, and death often follows within 10 years.
What causes the early
onset of juvenile HD?
Young persons with juvenile HD have usually inherited the disease from their fathers. The reason for this may be found in the process of sperm production. Unlike eggs, sperm are produced in the millions. Because DNA is copied millions of times during this process, scientists theorize that there is an increased possibility for genetic mistakes to occur.
What is late onset HD?
A few individuals develop HD after age 55. Diagnosis in these patients can be very difficult. The symptoms of HD may be masked by other health problems, or the person may not display the severity of symptoms seen in cases of an earlier onset of HD.
These sufferers may also show signs of depression rather than anger or irritability, or they may retain sharp control over their intellectual functions, such as memory, reasoning, and problem-solving.
What is senile chorea?
There is a related complex that bears the unfortunate name of "senile chorea." Some elderly victims display the symptoms of HD, especially choreic movements, but have a normal gene and lack a family history of the disorder.
Some scientists believe that a different gene mutation may account for this small number of cases. Others, however, believe senile chorea is a late onset form of HD.
How is HD diagnosed?
The great American folk singer and composer Woody Guthrie died on October 3, 1967, after suffering from HD for 13 years. He had been misdiagnosed, considered an alcoholic, and shuttled in and out of mental institutions and hospitals for years before being properly diagnosed. His case, sadly, is not extraordinary, although the diagnosis can be made easily by experienced neurologists.
The discovery of the HD gene in 1993 resulted in a direct genetic test to make or confirm a diagnosis of HD in a patient who is exhibiting HD-like symptoms. Using a blood sample, the genetic test analyzes DNA for the HD mutation by detecting the redundant genetic code of the HD gene.
The doctor will interview the patient to rule out other conditions and will perform an examination including tests for hearing, eye movements, strength, sensation, reflexes, balance, movement, and mental status. The doctor will also probably order a number of laboratory tests and inquire about recent intellectual or emotional problems.
The family history, sometimes called a pedigree or genealogy, is a critical part of the evaluation. It is extremely important for family members to be candid and truthful with a doctor who is taking a family medical history.
Sufferers of HD commonly have impairments in the way the eye follows or fixes on a moving target. Abnormalities of eye movements vary from person to person and differ depending on the stage and duration of the illness.
The physician may ask the individual to undergo a test that provides images of the brain. The computed tomography (CT) and magnetic resonance imaging (MRI) scans provide excellent images of brain structures with little if any discomfort. Those with HD may show shrinkage of some parts of the inner brain - particularly two areas known as the caudate nuclei and putamen - and enlargement of cavities within the brain called the ventricles. (These changes do not definitely indicate HD however, because they can also occur in other disorders.) In addition, a person can have early symptoms of HD and still have normal brain scans.
Other technologies for brain visualization, such as positron emission tomography
(PET), are an important part of HD research efforts, but their usefulness to physicians trying to diagnose HD has not yet been established.
What is the ethical dilemma
posed by HD?
Huntington disease represents a classic ethical dilemma created by knowledge of genes, i.e., that of the widening gap between what we can diagnose and what we can do anything about. Nancy Wexler, a leading HD researcher, poses the questions as follows:
Do you want to know how and when you are
going to die, especially if you have no power
to change the outcome?
Should such knowledge be made freely available?
How does a person choose to learn this
momentous information?
These questions are perhaps particularly piercing because Nancy Wexler is open about the fact that she is the child of a parent with HD, so she is at risk for developing the disease herself.
There are additional dilemmas for patients and doctors. In a small number of patients with HD -1 to 3 percent - no family history of HD can be found. Some individuals may not be aware of their genetic legacy, or a family member may conceal a genetic disorder from fear of social stigma. A parent may not want to worry children, scare them, or deter them from marrying.
What about testing for HD
before symptoms appear?
In other cases, a family member may die of another cause before he or she begins to show signs of HD. Sometimes, the cause of death for a relative may not be known, or the family is not aware of a relative's death. Adopted children may not know their genetic heritage, or early symptoms in an individual may be too slight to attract attention. These are among the many complicating factors
that reflect the complexity of diagnosing HD.
It is now possible to accurately identify persons carrying the HD gene 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. Testing may require a sample of DNA from a closely related affected relative, preferably a parent, for the purpose of confirming the diagnosis of HD in the family. This is especially important if the family history for HD is unclear or unusual in some way.
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).
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 pre-implantation 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.
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 this may 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, either from their testing center or from the organizations listed below. These organizations have 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.
How does someone decide
whether to be tested?
The anxiety that comes from living with a 50 percent risk for HD can be overwhelming.
How does a young person make important choices about long-term education, marriage, and children?
How do older parents of adult children cope with their fears about children and grandchildren?
How do people come to terms with the ambiguity and uncertainty of living at risk?
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 right 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.
Is there treatment for HD?
Doctors may prescribe a number of medications to help control the emotional and movement problems associated with HD. It is important to remember however, that while medicines may help keep these clinical symptoms under control, there currently is no treatment to stop or reverse the course of the disease.
Antipsychotic drugs, such as haloperidol (HALDOL), or other drugs, such as clonazepam (KLONOPIN), may help to alleviate choreic movements and may also be used to help control hallucinations, delusions, and violent outbursts.
Antipsychotic drugs, however, are not prescribed for another form of muscle contraction associated with HD, called dystonia, and may in fact worsen the condition, causing stiffness and rigidity. These medications may also have severe side effects, including sedation, and for that reason are used in the lowest possible doses.
For depression, physicians may prescribe fluoxetine (PROZAC), sertraline hydrochloride (ZOLOFT), nortriptyline (PAMELOR), or other compounds. Tranquilizers can help control anxiety and lithium may be prescribed to combat pathological excitement and severe mood swings. Medications may also be needed to treat the severe obsessive-compulsive rituals of some individuals with HD.
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.
NOTE: See A  Physician's Guide To HD To The Treatment of Huntington's Disease, 2nd Edition, for current treatment for HD symptoms.
What kind of care does
someone with HD need?
Although a psychologist or psychiatrist, a genetic counselor, and other specialists may be needed at different stages of the illness, usually the first step in diagnosis and in finding treatment is to consult a neurologist. While the family doctor may be able to diagnose HD, and may continue to monitor the patient's status, it is better to consult with a neurologist about management of the varied symptoms.
Problems may arise when affected individuals try to express complex thoughts in words they can no longer pronounce intelligibly. It can be helpful to repeat words back to the HD sufferer so that he or she knows that some thoughts are understood. Sometimes, people mistakenly assume that if individuals do not talk, they also do not understand.
Never isolate victims by not talking, and try to keep their environment as normal as possible. Speech therapy may improve the patient's ability to communicate.
It is extremely important for the person with HD to maintain physical fitness as much as his or her condition and the course of the disease allows. Persons who exercise and keep active tend to do better than those who do not. A daily regimen of exercise can help the patient feel better physically and mentally. Although their coordination may be poor, individuals should continue walking, with assistance if necessary.
Those who want to walk independently should be allowed to do so as long as possible, and careful attention should be given to keeping their environment free of hard, sharp objects. This will help ensure maximal independence while minimizing the risk of injury from a fall. Sufferers can also wear special padding during walks to help protect against injury from falls. Some people have found that small weights around the ankles can help stability. Wearing sturdy shoes that fit well can help too, especially shoes without laces that can be slipped on or off easily.
Impaired coordination may make it difficult for people with HD to feed themselves and to swallow. As the disease progresses, HD sufferers may even choke. In helping individuals to eat, caregivers should allow plenty of time for meals. Food can be cut into small pieces, softened, or pureed to ease swallowing and prevent choking. While some foods may require the addition of thickeners, other foods may need to be thinned.
Dairy products, in particular, tend to increase the secretion of mucus, which in turn increases the risk of choking.
Some patients may benefit from swallowing therapy, which is especially helpful if started before serious problems arise. Suction cups for plates, special tableware designed for people with disabilities, and plastic cups with tops can help prevent spilling. The individual's physician can offer additional advice about diet and about how to handle swallowing difficulties or gastrointestinal problems that might arise, such as incontinence or constipation.
Caregivers should pay attention to proper nutrition so that the person with HD consumes enough calories to maintain his or her body weight. Sometimes, people with HD, who may burn as many as 5,000 calories a day without gaining weight, require five meals a day to take in the necessary number of calories. Doctors may recommend vitamins or other nutritional supplements.
In a long-term care institution, staff will need to assist with meals in order to ensure that the individual's special caloric and nutritional requirements are met. Some individuals and their families choose to use a feeding tube; others choose not to.
Individuals with HD are at special risk for dehydration and therefore require large quantities of fluids, especially during hot weather. Bendable straws can make drinking easier for the person. In some cases, water may have to be thickened with commercial additives to give it the consistency of syrup or honey.
What community resources
are available for HD?
Individuals and families affected by HD can take steps to ensure that they receive the best advice and care possible. Doctors and state and local health service agencies can provide information on community resources and family support groups that may exist. Possible types of help include:
Legal and social aid:
HD affects a person's capacity to reason, make judgments, and handle responsibilities. Individuals may need help with affairs. Wills and other important documents should be drawn up early to avoid legal problems when the person with HD may no longer be able to represent his or her own interests. Family members should also seek assistance if they face discrimination regarding insurance, employment, or other matters.
Home care services:
Caring for a person with HD at home can be exhausting, but part-time assistance with household chores or physical care of the individual can ease this burden. Domestic help, meal programs, nursing assistance, occupational therapy, or other home services may be available from federal, state, or local health service agencies.
Recreation and work centers:
Many people with HD are eager and able to participate in activities outside the home. Therapeutic work and recreation centers provide individuals an opportunity to pursue hobbies and interests and to meet new people.
Participation in these programs, including occupational, music, and recreational therapy, can reduce the person's dependence on family members and provides home caregivers with a temporary, much needed break.
Group housing:
A few communities have group housing facilities that are supervised by a resident attendant and that provide meals, housekeeping services, social activities, and local transportation services for residents.
These living arrangements are particularly suited to the needs of individuals who are alone and who, although still independent and capable, risk injury when they undertake routine chores like cooking and cleaning.
Institutional care:
The individual's physical and emotional demands on the family may eventually become overwhelming. While many families may prefer to keep relatives with HD at home whenever possible, a long-term care facility may prove to be best.
To hospitalize or place a family member in a care facility is a difficult decision; professional counseling can help families with this process. Finding the proper facility can itself prove difficult. Organizations such as the Huntington's Disease Society of America may be able to refer the family to facilities that have met standards set for the care of individuals with HD.
Very few of these exist however, and even fewer have experience with
individuals with juvenile or early-onset HD who require special care
because of their age and symptoms.
How long do people with
Huntington disease live?
In general, the duration of the illness from the time the first signs become evident ranges from 10 to 30 years. The most common causes of death are infection (most often pneumonia), injuries related to a fall, or other complications.
Where are some of the resources
for Huntington disease?
NIH Neurological Institute
P.O. Box 5801
Bethesda, MD 20824
(301) 496-5751
1-(800) 352-9424
Huntington's Disease Society of America (HDSA)
158 West 29th Street, 7th Floor
New York, NY 10001-5300
(212) 242-1968
1-(800) 345-HDSA (345-4372)
www.hdsa.org
Hereditary Disease Foundation
1427 Seventh Street, Suite 2
Santa Monica, CA 90401
(310) 458-4183
http://www.hdfoundation.org/ | |
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