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Human brain -

Huntington's disease (HD) is a rare, inherited condition caused by the progressive breakdown, or degeneration, of nerve cells in the brain.

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Faulty gene -

The illness stems from a faulty gene in a person's DNA, the molecule that carries genetic information for the development and functioning of the body and keeps it running.

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Nervous system -

If you have Huntington's, it affects your body's nervous system, resulting in a broad impact on functional ability. The disorder invariably results in movement, thinking (cognitive), and psychiatric disorders.

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Symptoms -

The onset of HD is revealed by a set of symptoms that can vary widely from person to person. Telltale signs include a variety of movement disorders such as involuntary jerking or writhing movements, a condition known as chorea.

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Dystonia -

HD also causes muscle problems, for example rigidity or uncontrollable muscle contracture, a disorder called dystonia.

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Impaired gait -

Chorea and dystonia impact on stability and coordination, resulting in an impaired gait, stumbling, and clumsiness.

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Difficulty swallowing -

Other movement disorders associated with Huntington's can include slurred speech and difficulty swallowing. This latter condition eventually results in significant weight loss.

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Cognitive disorders -

The physical affects of HD extend to a raft of cognitive impairments. A progressive lapse of memory is a typical symptom.

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Difficulty concentrating -

Difficultly concentrating and prioritizing or focusing on tasks are also symptomatic of the condition, as is trouble with learning and retaining new information.

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Lack of impulse control -

The lack of impulse control HD sometimes induces can result in outbursts, acting without thinking, mood swings, and personality changes.

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Perseveration -

Sufferers of HD often demonstrate a complete lack of mental flexibility, a condition known as perseveration—when someone "gets stuck" on a topic, idea, or behavior.

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Psychiatric disorders -

One of the most damaging of early HD psychiatric disorders is depression. A confirmed diagnosis of this debilitating and fatal disease often kick-starts a cycle of mental instability, with thoughts of death, dying, and even taking one's own life frequently brought to the fore.

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Clinical depression -

Signs and symptoms associated with clinical depression include irritability, apathy, and, very often, profound melancholy.

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Social withdrawal -

As the enormity of their condition slowly sinks in, sufferers of HD socially withdraw, sometimes to the point of social isolation.

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Fatigue -

With such a weight on their shoulders, it's no wonder that many of those stricken with HD end up suffering from chronic fatigue and a total lack of energy.

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Juvenile Huntington's disease -

While less than 10% of people with Huntington's will have Juvenile-onset, the sad fact is that the disease can sometimes appear in children. Early symptoms are defined by behavioral changes such as difficulty paying attention and a rapid and alarming drop in overall school performance.

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Physical changes -

As with adult sufferers, physical changes in a child with HD include chorea, frequent falls and clumsiness, and seizures.

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Causes of Huntington's disease -

Huntington's disease is caused by an inherited defect in a single gene. But how does this errant gene develop, and how is it passed on? The DNA error that causes HD is found in a gene called huntingtin.

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How it's inherited -

Everyone has the huntingtin gene, but only those that inherit the mistake, known as the HD mutation, will develop HD and risk passing it on to their children. This image illustrates a normal huntingtin gene sequence (top), while below is a huntingtin mutation.

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How is HD passed on? -

If someone has this faulty gene, they will develop HD. The disease is passed down in families from generation to generation. But in a cruel game of chance, a child inherits two copies of every gene—one copy from each parent. A parent with a defective gene could pass along the defective copy of the gene or the healthy copy. Each child in the family, therefore, has a 50% chance of inheriting the gene that causes the genetic disorder.

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Prevention -

All children who are conceived naturally to a parent with the faulty HD gene stand a 50% chance of inheriting the disease. And, of course, people with a known family history of Huntington's disease are understandably concerned about whether they may pass the defective gene on to their children. But how do you know if you're carrying a Huntington gene? One way is to opt for genetic testing.

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Genetic testing -

Genetic testing is only carried out after a meeting with a genetic counselor. A test will determine whether a patient is positive or negative for the defective gene. The procedure involves checking a sample of blood for the genetic fault that causes the condition.

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In vitro fertilization -

The results of the test serve a double purpose. It can be used to diagnose the condition in the first instance, and check if your child will develop it later in life. Couples wishing to start a family face a dilemma. They will have to choose whether to have children at all, or consider alternatives, such as in vitro fertilization with donor sperm or eggs. Any decision has widespread implications and is why professional counseling is mandatory beforehand.

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Middle stages -

The rate of HD progression and duration varies. The time from disease emergence to death is often about 10 to 30 years. Juvenile Huntington's is less forgiving, the condition usually resulting in death within a decade after symptoms develop. In its middle stages HD is still manageable, but persistent weight loss for example can worsen symptoms and weaken the patient's immune system, making them more vulnerable to infections and other complications.

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Dietary requirements -

A nutritionist can help counter the effects of malnourishment by designing a high-calorie diet.

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Treatment and medical support -

As HD progresses, the emotional, mental, social, and economic impact on the life of an individual will be considerable. Physically, too, the patient will show a marked decline in mobility and will eventually require assistance with the most basic of tasks.

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Medicine -

Carefully prescribed medicines can help reduce some of the problems caused by Huntington's, for example easing mood swings and inhibiting involuntary movement. Antidepressants can help dissipate the awful cloud that is depression.

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Social and community support -

As the condition worsens, the emphasis turns to quality of life. By now a strong and effective social and community support network should be in place, with family, friends, and loved ones assuming many of the patient's former responsibilities.

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Later stages -

In the later stages of the disease, the person will no longer be able to walk or talk and will need full-time bedbound nursing care.

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Hope for the future -

While there is currently no cure for Huntington's disease, scientists hope that in the future gene therapy will find a solution to the condition, with some studies suggesting a method involving "cutting and pasting" DNA could become a groundbreaking technique in the battle against the disorder.

Sources: (Huntington's Disease Society of America) (Huntington's Disease Association) (MDS) (Huntington's Disease News) (Journal of Clinical Investigation)

See also: 30 strange facts you didn't know about DNA

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