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An Introductory Guide to Huntington Disease

 This guide is designed to be a primer for those who are seeking information about Huntington Disease (HD).

HD, previously known as Huntington's chorea, is an inherited genetic disorder that causes the deterioration of nerve cells in the brain. Over a period of time, this deterioration affects movement, behavior, and cognition, and eventually impedes the individual's ability to function normally. The symptoms of HD are often described as a combination of Parkinson's, ALS, and Alzheimer's. The symptoms can appear at any age, but usually become noticeable between the ages of 30 and 50.

 
What Causes Huntington's?

HD is caused by a defective gene inherited from a parent, with only 5-10% of cases resulting from a new genetic mutation. Since it is an autosomal dominant disorder, it means that only one copy of the defective gene, inherited from one parent, is necessary to produce the disease. Therefore, if one parent has the disease, each child has a 50% chance of inheriting the defective gene.

Males and females are both at equal risk of acquiring HD, but the disease occurs in certain races and ethnicities more than others, with people of European descent having a higher risk of acquiring it.

Per million, HD affects:

  • 40-120 people in Europe of European descent
  • 100 people in the U.S.A.
  • 1-7 people in Asia
  • 0.6 people of African descent

Note: The African figure might be so low due to poor documentation and inconclusive evidence.

What Are the Symptoms of Huntington's?

There are many symptoms which are indicative of HD, however, not everyone with the disorder will experience them to the same degree. Evidence also suggests that the average age of onset is later for individuals who inherited the gene from their mother. This means that, typically, onset occurs earlier when the gene is inherited from the father.

During the early stages of HD, people can function normally at home and work. However, as the disease progresses they may find it increasingly difficult to work or manage a household, but are still capable of dealing with most day-to-day activities. In the advanced stages of HD, involuntary movements give way to rigidity, communication and swallowing become severely impaired, and affected individuals will become severely impaired, and totally dependent on others.

The lifespan of somebody with HD varies, however, death typically occurs 15-25 years after the onset of the disease. This is usually due to complications such as heart failure, choking, infections, or pneumonia, and not from HD itself. In roughly 9% of cases, suicide is the cause of death.

The symptoms of HD can be split into physical changes, cognitive impairments, and psychiatric disorders.

Physical Changes
The movement disorders associated with HD can include both involuntary movements and impaired voluntary movements.

Involuntary movements which may originally consist of fidgeting, twitching of the hands or feet, or excessive restlessness, will slowly develop into more obvious uncontrollable jerking and twitching of the head, neck, arms, and legs. 

Diminished coordination, initially affecting things like driving and handwriting, becomes increasingly pronounced. Gait, posture, and balance become impaired and, as a result, during the later stages of the disease, people stagger when walking. Eventually, they will lose the ability to walk and control their movements all together.

Other physical changes include weight loss, muscle problems, slow or abnormal eye movements, and slurred speech.

Psychiatric Disorders

Depression is one of the most common psychiatric disorders associated with HD. In addition to the constant feelings of sadness and worthlessness, and a lack of desire to engage in formerly pleasurable activities, other signs of depression may include a lack of energy, insomnia, social withdrawal, irritability, apathy, and frequent thoughts of death, dying or suicide. Depression occurs as a result of changes in the brain due to HD, and not simply as a reaction to receiving the diagnosis.

Another psychiatric disorder associated with HD is Obsessive Compulsive Disorder. This condition causes severe anxiety and is characterized by recurrent, unwanted thoughts, and repetitive behaviors.

Cognitive Impairments
Those who are suffering from HD will experience cognitive changes which affect their awareness, judgment, and perception.

Therefore, affected individuals will have difficulty organizing, prioritizing, making decisions, and focusing on tasks. As a result, their jobs often become very time-consuming. During the later stages of the disease, some people prefer to take on jobs that are less demanding rather than having to give up work entirely. The ability to recall information (be it old or new), process thoughts, and "find" the right words diminishes so people with HD might appear forgetful.

Furthermore, coping with new situations becomes increasingly difficult and individuals may exhibit a lack of flexibility when it comes down to communicating with words, phrases, or gestures. Other symptoms include a lack of impulse control that can lead to outbursts, acting without thinking, and sexual promiscuity.

 
How Is Huntington's Diagnosed?
Several of the symptoms and signs of HD can be caused by many different conditions. Therefore, if you or someone close to you has any aforementioned signs or symptoms associated with HD, you should consult a doctor who will probably refer you to a neurologist. You will then undergo a thorough examination which will include a physical exam, a review of your family's medical history, neurological tests, a psychiatric evaluation, and brain imaging. If the results suggest that you may have HD, your neurologist might suggest that you take a genetic test to confirm whether you carry the defective gene.

Genetic Testing
If one of your parents has HD, but you haven't any symptoms and you'd like to find out whether you carry the gene, you can take a genetic test from the age of 18. Some take the test because they find it stressful not knowing if they will develop the disease. Others, on the other hand, prefer not to know if they've inherited the faulty gene as there are no treatments as of yet that can reverse the effects of the disease.

If you know that your partner carries the defective gene and are expecting a child, a genetic test can be carried out at 11 weeks into the pregnancy to reveal if the baby has the defective gene or not. If one of you is at risk of having HD, but would prefer not to know, one option is preimplantation genetic diagnosis. This allows the embryo to be tested for the disease and only implanted into the womb if it doesn't have the gene and is not at risk of developing HD after In Vitro Fertilization (IVF) has been performed.

Juvenile Huntington's
If someone develops HD before the age of 20, it is known as Juvenile Huntington Disease. However, only 5-10% of people with the disease are affected by it. The onset and progression of symptoms may differ from those in adults. The problems that occur in the early stages include:

Behavioral changes:
• Children and young adults experience a loss of previously learned academic or physical skills.
• A rapid, and significant drop in school performance.
• Behavioral problems can arise. 

Physical changes:
• Muscles become contracted and rigid, affecting gait.
• Changes in fine motor skills that is noticeable in, for example, handwriting.
• Young people can experience seizures in addition to tremors or involuntary movement. 

Living with Huntington's
As the disease advances, individuals with HD will undergo a number of physical and mental changes so it's important for them and their loved ones to have a clear understanding of the changes that they will have to make in order to allow them to remain as independent as possible.

Eating can become frustrating during the later stages of the disease, so in order to help with this any food should be easy to chew, swallow, and digest. To avoid choking, food should be cut into small pieces or pureed. Furthermore, adapted cutlery and straws, as well as non-slip mats can make eating easier for affected individuals. At later stages of the disease a person may choose to be fed through a tube.

As mobility and balance become affected, social services and occupational therapists can help people with HD to adapt to their homes so that day-to-day living is easier. a person's shower, toilet, bath, chairs, and bed may need to be modified, and during the later stages of the disease the home may need to be adapted to make them wheelchair friendly.

What Treatment Is Available to Individuals with Huntington's?
Unfortunately, there is no cure for HD, but although the mental, physical and behavioral decline can't be slowed down or reversed, there is medication available that can help manage the symptoms. The following treatments and therapies have been found to be effective in managing some of the symptoms of HD.

Therapies
• Speech and language therapy can help to improve communication skills as well as memory. Language therapy can teach HD sufferers alternative ways of communicating aside from talking. 
• Physiotherapy can help a HD patient maintain/regain mobility and balance. Treatments such as massages, muscle manipulation, exercise, electrotherapy, and hydrotherapy can be very effective. 
• Regular exercise is very important for those affected by HD. Individuals with this disease who exercise feel a lot better both physically and mentally than those who don't exercise. 

Medications
Medications can be prescribed by a doctor to help manage some of the symptoms of HD, but most of them have side effects so many patients decide not to take them. 
• A variety of antidepressants can be taken to improve mood swings. However, the side effects include nausea, constipation, diarrhea, excessive sweating, insomnia, trembling or shaking, and low blood pressure. 
• Mood stabilizers can treat mood swings and irritability. The side effects may include weight gain, gastrointestinal problems, and tremors. 
• Antipsychotic medication can be used to control delusions and violent outbursts. However, doctors usually prescribed the lowest dose possible as they can have very severe side effects. This includes drowsiness, nausea, and restlessness. They can also trigger depression or other psychiatric conditions. 

In order to manage symptoms, it's crucial that the patient's treatment goals and medication plan are regularly reviewed and analyzed by a specialist.

 

Source junomedical

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