Huntington's Disease Bibliography

Huntington's Disease Questions

Huntington’s Disease

By: Ashley W., Sophia A., Keiana D., Deanna S.
Also known as:
Huntington Chronic Progressive Hereditary Chorea
Huntington's Disease
Progressive Chorea, Chronic Hereditary (Huntington)

I. Characteristics of Huntington's Disease
Huntington’s Disease is a hereditary, degenerative brain disorder characterized by the loss of ability to walk, talk, and reason. The symptoms of Huntington’s can be separated into the following three categories:
-- Behavioral/emotional
o Irritability
o Depression
o Anxiety
o Aggressive outbursts
o Mood swings
o Social withdrawal

o Fidgety behavior
o Problems with coordination
o Involuntary movements (chorea, dystonia)
o Difficulties with speech, swallowing, balance, walking

o Problems with short-term memory, organizing, coping, and concentrating

Huntington’s disease symptoms typically begin to appear between the ages of 30 and 50. There are two forms of Huntington's Disease: adult-onset HD and early-onset HD. Early onset HD may occur as early as the age of 2. The early symptoms of HD include depression, mood swings, forgetfulness, clumsiness, involuntary twitching and lack of coordination. As the disease progresses, the other symptoms become apparent. Once symptoms begin to show, the life expectancy of HD patients is between 10 to 15 years.
This is a picture of the scientist George Huntington who originally identified HD as a hereditary disorder.
This is a picture of the scientist George Huntington who originally identified HD as a hereditary disorder.

Here is a video explaining the basics of Huntington's Disease: Huntington's Disease by Sue Wright

What is the frequency of HD around the world?
Huntington’s disease is currently found in many different countries and ethnic groups around the world. The highest frequencies of HD are found in Europe and countries of European origin, such as the United States and Australia. The lowest documented frequencies of HD are found in Africa, China, Japan, and Finland.

|| Population
Frequency of HD
(cases per million people)
South Africa (blacks)
Hong Kong
Europe & countries
of European descent
-Northern Ireland
-South Wales
-Scotland (Grampian Region)
-United States

II. What type of mutation causes Huntington's?
HD is caused by a repeated extension of the DNA segment CAG. A mutation in the HTT gene on chromosome 4 causes this disorder. A protein called huntingtin is made from the instructions provided by the HTT gene. The function of this protein in unknown but it seems to be an
important part of the nerve cells in the brain. The HTT mutation involves a DNA segment known as CAG (cytosine, adenine, and guanine). Within the HTT gene the normal CAG segment is repeated 10 to 35 times. For people who have HD, the CAG segment is repeated 36 to over 40 times. When the CAG segment is increasingly larger than normal it leads to the production of an abnormally long version of the huntingtin protein. This protein disrupts the functions of cells by being cut into small, toxic fragments that join together and gather in neurons. The signs and symptoms of Huntington’s disease are caused by the dysfunction and eventual death of the neurons in specific areas of the brain.

III. How is Huntington's inherited?

Huntington’s Disease is an autosomal dominant disorder so only one copy of the altered HTT gene from a parent can trigger the disease in a child. Each child of a parent with Huntington’s has a 50% chance of inheriting the gene. It is not possible for HD to skip generations in families. Although it is very rare, it is possible for a HD patient to not have a parent with the disease. As the altered HTT gene gets passed down generations, the abnormally long CAG chain grows longer which causes the HD symptoms to begin appearing at earlier ages. For this reason, people with adult-onset HD have 40 to 50 CAG repeats in the HTT gene while early-onset patients usually have over 60 repeats. People who have only 27 to 35 CAG repeats do not develop HD but it is still possible for their children to inherit and show the symptoms of HD.

This chart shows how the altered HTT gene can get passed down through generations.
This chart shows how the altered HTT gene can get passed down through generations.

IV. Have any medical advancements been developed to treat or prevent Huntington's Disease?

There has not been any medical advancements developed to fully cure this disorder but there are treatments to slow down its process and help control the person's emotions and movements for as long as possible. Depending on the symptoms the person shows the medications vary. To reduce abnormal behaviors and movements the use of Dopamine blockers may help. To control extra movements drugs such as haloperidol, tetrabenazine, and amantadine are used.
Most of the medicines prescribed to patients with HD come with side effects such as fatigue, restlessness, and hyperexcitablility. It is very significant that people with HD stay active and healthy because individuals who excercise tend to do better than those who don't. It is common for people with HD to have thoughts of suicide and feel depressed. If you are someone caring for a person with HD, it is crucial that you observe their symptoms and treat them appropriately.

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