The Basics of Huntington's Disease
Part 1

A basic explanation of the biological basis of Huntington’s disease.

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Huntington's disease (often abbreviated "HD") was first described in medical literature in 1872 by Dr. George Huntington, a physician from Long Island, New York. The disease affects men and women alike, occurring at a rate of about one in every 10,000 in most Western countries. People with HD need dedicated care and support from their loved ones, which makes the number of lives touched by the disease even greater.

The age of onset of Huntington’s disease is normally between 30 and 50 years old, although there is also a form of HD that affects children and teenagers. People with HD may express a wide variety of symptoms, which physicians typically group into three categories: movement, cognitive, and psychiatric symptoms.

• Some of the movement symptoms of HD include muscle spasms, tics, rigidity, falling down, difficulty physically producing speech, and, in the later stages of the disease, difficulty swallowing (which can lead to significant weight loss). Uncontrollable movements such as writhing and twisting are also quite common symptoms of HD. Physicians sometimes refer to these uncontrollable movements as “chorea”.

• The most significant cognitive symptoms of HD are the altered organization and generally slowed processing of information in the brain. These symptoms can lead to difficulty learning new things, difficulty planning and prioritizing, impairment of one’s perception of space (where one is in relation to tables, walls, etc.), and difficulty “multitasking” (paying attention to several things at once). Individuals frequently adhere to common routines because these routines are the easiest for them to accomplish. Finally, because they have trouble organizing incoming and outgoing words in their brains, many people with HD experience difficulty communicating with others.

• Depression is the most common of the psychiatric symptoms of HD. Other symptoms include personality changes, apathy, anxiety, irritability, obsession with certain activities (such as hand washing), delirium, and mania. Denial of having HD is also a common symptom of the disease.

Sadly, somewhere between 10 and 25 years after symptoms first appear, HD usually takes such a toll on individuals that they die of pneumonia, heart failure, or other complications.

HD causes deterioration of the nerve cells in the brain, prompting significant changes in one's ability to think, feel, and move. The cause of these symptoms remained a mystery for quite some time until doctors noticed that the disease "ran in families" and suspected its hereditary basis. The inheritance of HD (like other hereditary traits) is now known to depend upon a "chemical code" of information contained in a substance called deoxyribonucleic acid, or DNA, which exists within living cells. Understanding a bit about this chemical code helps to give better insight into the causes of HD and into treatments that may one day lead to its cure.

The chemical code of DNA is a lot like the English language: both use specific letters in a specific order to communicate specific things. But while the English language has 26 letters, the DNA code only has four--A, C, G, and T (which stand for chemical subunits of DNA). Also, while English words can consist of either a few or many letters, DNA "words" are always three letters long. In the study of genetics, these three-letter "words" are called codons. Aptly named, codons code for the future building that goes on in the nerve cell. They are a bit like blueprints. Consider this example: when a passage contains the letters C-A-T in English, this paints a picture of our favorite lazy pet. In much the same manner, when the code of DNA contains the letters G-G-C, this tells the cell to build with proline, an amino acid. For more about DNA, click:

If codons are like blueprints, then we can think of the amino acids that result from them as unique building blocks. When these blocks are put together chemically, they create a structure known as a protein. Like buildings in modern society, proteins are where the work of the nerve cell gets done. Proteins have many different jobs: they help the cell maintain its structure, produce energy, and communicate with other cells. If it were not for the body's millions of proteins, life as we know it could not occur.

Last Modified: 11-6-04

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