Huntington’s Disease – Causes, Signs and symptoms

Huntington Disease

Also called: Huntington’s Chorea, Huntington’s Chorea Disease

Summary

Huntington’s disease (HD) is an inherited disorder of the brain that slowly destroys a person’s ability to think, feel and move. The disease is incurable and progresses until it causes the patient’s death. About 30,000 people in the United States have HD, according to the National Institutes of Health.

HD is caused by a gene mutation that affects the way certain chemicals are produced in the brain. This results in the death of nerve cells (neurons) in several parts of the brain. The genetic mutation that causes HD is passed down from parent to child. Children whose parents have the HD gene have a 50 percent chance of inheriting the gene that causes the disease.

HD most often appears during adulthood, especially between the ages of 35 and 50. In some cases, people may develop the disease earlier in life. In general, the earlier the disease develops, the faster it progresses.

HD is characterized by involuntary, dancing-like movements called chorea. This movement disorder is the result of neuron death in part of the brain (called the basal ganglia) that is associated with movement and balance. Other symptoms of HD include dementia and emotional and behavioral problems.

In diagnosing HD, a physician will typically perform a physical examination and compile a medical history. If Huntington’s disease is suspected, the patient may be referred to a neurologist. An important aspect of diagnosis is evidence of a family history of the disease. Genetic testing may also be conducted to look for the mutated gene in the patient’s DNA structure.

There is no cure for HD, and the progression of the disease cannot be delayed or halted. Treatment usually focuses on controlling symptoms and maintaining a reasonable quality of life for as long as possible. This may include using medications or other supportive treatment methods.

Although HD cannot be prevented, people can receive genetic tests that indicate whether or not they are carriers of the gene responsible for this illness. This information has the potential to create great emotional distress for some people. However, the benefit of genetic testing is identifying people who are carriers of the gene so they are better able to make informed decisions about the risks involved with having children.

Risk factors and causes of Huntington’s disease

Huntington’s disease (HD) is an inherited illness passed on to children from their parents. It is caused by the mutation of a single gene located on chromosome 4. HD is an autosomal dominant disorder, which means that only one parent must carry the gene mutation for the disease to be passed to a child. If one parent has the gene mutation, there is a 50 percent likelihood that the mutation will be passed to a child. This risk is the same for each pregnancy.

In between 1 and 3 percent of cases, no family history of HD can be found. In these cases, it is believed that the genes have spontaneously mutated during the father’s sperm development. Children who have this spontaneous mutation in their genes may pass the mutation to future generations.

The gene that is mutated in people with HD is responsible for producing a protein called Huntingtin. The altered production of this protein has several consequences, most of which are poorly understood by scientists. One consequence of the altered protein is the increase of neurotransmitter levels, which, in turn, leads to the degeneration of neurons in certain parts of the brain. Neurons in the basal ganglia, which control aspects of movement and balance, are typically first affected. The brain’s outer surface (cortex) also may be affected. This is the area of the brain that controls memory, perception and thought.

HD affects males and females in equal numbers and affects all ethnic groups.

Signs and symptoms of Huntington’s disease

Patients with Huntington’s disease (HD) may develop symptoms at varying rates. In some cases, symptoms gradually develop as neurons degenerate. In other cases, symptoms may come on more quickly. As a general rule, the earlier symptoms appear, the quicker the disease is likely to progress.

The characteristic symptom of HD is chorea, which are uncontrolled, jerking movements of the face, arms, legs or trunk. They are often described as being dance-like. Symptoms related to chorea generally become more severe and debilitating as the disease progresses. Chorea may also become more severe when the patient is anxious or agitated. Movement problems related to chorea include:

  • Difficulties walking
  • Unsteadiness
  • Lack of coordination
  • Slurred speech
  • Difficulty swallowing

People with HD may also experience emotional and behavioral problems. These are usually noticed early in the course of the disease and may develop before movement is affected. Patients may experience mood swings that include bouts of depression, irritability, apathy and passivity. Studies have shown that people with HD are also at an increased risk for other psychiatric problems, such as obsessive compulsive disorder (OCD) or schizophrenia.

As the disease progresses, people with HD may also experience symptoms of dementia, including:

  • Memory loss
  • Difficulty learning new tasks
  • Hallucinations and delirium
  • Poor judgment

Most symptoms of HD tend to become more severe as the disease progresses. However, in some cases, mood swings subside as other symptoms get worse. Patients with HD may eventually have difficulty feeding and otherwise looking after themselves.

Diabetes, an endocrine system disorder, appears to be associated with HD. Studies have shown an increased rate of diabetes among patients with HD.  

Young people with HD may experience age-specific symptoms that often mimic Parkinson’s disease. Such symptoms include slowness of movement, rigidity and tremor. Young people with HD also may experience seizures.

Diagnosis methods for Huntington’s disease

A physician may suspect Huntington’s disease (HD) in patients who develop movement disorders in addition to behavioral problems and dementia. Because of the slow progression rate of the disease in some people, HD may be diagnosed after several years of the initial onset of the disease. If Huntington’s disease is suspected, the patient may be referred to a neurologist.  

In diagnosing Huntington’s disease (HD), a physician will perform a complete physical examination. Patients may undergo a neurological examination. During these examinations, several aspects of the patient’s health may be tested, including:

  • Balance
  • Coordination
  • Eye movements
  • Hearing
  • Mental status
  • Movement
  • Vision

In addition to a physical examination, the physician will also compile a thorough medical history and investigate whether there is a family history of the disease. Children of parents with HD have a 50 percent chance of developing the disease. Therefore, a family history of HD in addition to the onset of symptoms is a strong indicator of HD.

In some cases, especially if there is no family history of HD, the physician may recommend a genetic test in order to look for the mutated gene in the patient’s DNA. For a genetic test, a physician takes a sample of the patient’s blood to identify whether the mutated gene is present.

Imaging tests, such as computed axial tomography (CAT) scans and magnetic resonance imaging (MRI) are sometimes used to rule out other conditions and support a diagnosis of HD.

Some people with a family history of HD may wish to undergo pre-symptomatic testing in order to determine whether they will develop the disease. This may involve a neurological examination and genetic test to look for signs and symptoms of the disease. Genetic counseling is also a recommended component of pre-symptomatic testing. Genetic counselors are people who are trained in aspects of genetics and are able to discuss the implications of genetic test results with patients. This may be especially helpful for couples with a family history of HD who are contemplating having a child.

Treatment options for Huntington’s disease

There is no cure for Huntington’s disease (HD) and the progression of the disease cannot be slowed down or halted. Generally, treatment for HD is aimed at reducing the patient’s symptoms and maintaining a good quality of life for as long as possible.

Several medications are available to help control symptoms related to HD. For example, dopamine blockers and depletors and antidyskinetics may be used to treat and control movement problems. Additionally, antidepressants and tranquilizers can help reduce emotional symptoms such as mood swings and depression. Other symptoms, such as delusions, hallucinations and psychosis may be treated using antipsychotic drugs.

Although these drugs are effective for many patients, most of them cause several side effects, including fatigue, hyperexcitability and restlessness.

There are also several self-care measures that patients can take to help reduce their symptoms. For example HD patients who remain physically active are less prone to falls and other consequences of their movement problems. Patients may also benefit from speech therapy and other forms of therapy (e.g., occupational or physical therapy) that can help them deal with the symptoms of their illness.

Proper nutrition is an important part of coping with HD. People with HD may burn as many as 5,000 calories in a day because of their excess movements. This may result in malnourishment and dehydration in some patients. People with HD should ensure that they get adequate nutrition to maintain their body weight and drink plenty of fluids to reduce the risk of dehydration. Additionally, eating is often complicated for HD patients because they may have trouble swallowing. Occupational therapists can also help teach patients how to improve their swallowing technique.

Finally, many patients with HD experience emotional difficulties, both as a symptom of the disease and as a result of living with HD. Sessions with a therapist or participation in a support group can help make this aspect of the disease more manageable.

Prevention methods for Huntington’s disease

Huntington’s disease (HD) cannot be prevented. People who have inherited the mutated gene responsible for HD are guaranteed to develop the disease at some point in their life.

Because of this inevitability, people with a family history of the disease may wish to undergo testing and counseling to determine what risk that they or their children have of developing the disease. This information has the potential to create great emotional distress for some people, and the implications should be carefully considered before these types of tests are undergone. However, people who know they are carriers of the gene are better able to make informed decisions about the risks of having children.

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