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Genetic and Rare Diseases Information Center (GARD)

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Huntington disease

Other Names for this Disease
  • HD
  • Huntington chorea
  • Huntington's chorea
  • Huntington's disease
See Disclaimer regarding information on this site. Some links on this page may take you to organizations outside of the National Institutes of Health.

Your Question

A friend of mine has been diagnosed with Huntington disease. No one else in his family has this condition. Is it possible that a chemical exposure could have caused it, such as to vinyl chloride?

Our Answer

We have identified the following information that we hope you find helpful. If you still have questions, please contact us.

What causes Huntington disease?

Huntington disease (HD) is caused by a mutation in the HTT gene. This gene gives instructions for making a protein called huntingtin. The exact function of this protein is unclear, but it appears to be important to nerve cells (neurons) in the brain.

The HTT gene mutation that causes HD involves a DNA segment known as a CAG trinucleotide repeat. This segment is made up of 3 DNA building blocks that repeat multiple times in a row. The CAG segment in a normal HTT gene repeats about 10 to 35 times. In people with HD, it may repeat from 36 to over 120 times. People with 36 to 39 CAG repeats (an intermediate size) may or may not develop HD, while people with 40 or more repeats almost always develop HD.

An increased number of CAG repeats leads to an abnormally long version of the huntingtin protein. The long protein is then cut into smaller, toxic pieces that end up sticking together and accumulating in neurons. This disrupts the function of the neurons, ultimately causing the features of HD.[1]
Last updated: 4/23/2015

Can people without a family history of Huntington disease still develop the condition?

Yes. While most people with Huntington disease (HD) inherit it from an affected parent, in rare cases a person has HD due to having a de novo mutation in the HTT gene (a mutation that occurs for the first time and is not inherited from a parent). However, the family history can sometimes appear negative for various reasons even though a parent carries, or carried, a mutation.[2]
Last updated: 4/23/2015

Can environmental exposures cause gene expansion like that of the CAG repeat that causes Huntington disease?

We were unable to find information in the medical literature regarding an association between exposure to vinyl chloride (or other substance) and CAG repeat expansion or Huntington disease. We were however able to identify the following articles which may be of interest to you. The first one listed below discusses the differences in the age of onset of Huntington disease in identical twins and the possible role of environmental factors. The second article discusses how certain gene changes in combination with environmental exposures may have a role in causing disease. 

Freidman JH et al., Monozygotic Twins Discordant for Huntington Disease After 7 Years. Arch Neurol. 2005;62:995-997.
Christiani DC, Mehta AJ, Yu CL. Genetic susceptibility to occupational exposures. Occup Environ Med. 2008 Jun;65(6):430-6; quiz 436, 397.

The first article is available in free full text. To obtain a copy of the following article, contact a medical, university, or local library. You can call the National Library of Medicine toll-free at 888-346-3656 to locate libraries in your area that can provide direct access to journals. You can also purchase the article online by clicking on the link above.

Last updated: 1/3/2009

Are there certain chemicals or substances that people with Huntington disease should avoid?

Yes. There are certain compounds that can be particularly problematic for people with Huntington disease, such as L-dopa-containing compounds which may increase chorea, and alcohol and smoking. If you or someone you know has Huntington disease we recommend that you speak with a healthcare provider to learn more about what substances to avoid.
Last updated: 1/3/2009

Who can I contact to learn more about genetic disease and environmental exposure?

We recommend that you contact the National Institute of Environmental Health Sciences (NIEHS). The NIEHS strives to reduce the burden of human illness and dysfunction from environmental causes by defining how environmental exposures, genetic susceptibility, and age interact to affect an individual’s health. 

National Institute of Environmental Health Sciences
P.O. Box 12233
Research Triangle Park, NC 27709

Telephone: 919-541-3345
TTY: 919-541-4644
Web site:

Last updated: 1/3/2009

How can I find a genetics professional in my area?

Genetics clinics are a source of information for individuals and families regarding genetic conditions, treatment, inheritance, and genetic risks to other family members. More information about genetic consultations is available from Genetics Home Reference. To find a genetics clinic, we recommend that you contact your primary healthcare provider for a referral.

The following online resources can help you find a genetics professional in your community:

Last updated: 11/27/2014

How can I learn about research involving Huntington disease?

The U.S. National Institutes of Health, through the National Library of Medicine, developed to provide patients, family members, and members of the public with current information on clinical research studies. Currently clinical trials are identified as enrolling individuals with Huntington disease. To find these trials, click on the link below. After you click on a study, review its 'eligibility' criteria to determine its appropriateness. Use the study’s contact information to learn more. Check this site often for regular updates.

You can also contact the Patient Recruitment and Public Liaison (PRPL) Office at the National Institutes of Health (NIH). We recommend calling the toll-free number listed below to speak with a specialist who can help you determine if you or someone you know is eligible for any clinical trials.  

Patient Recruitment and Public Liaison Office
NIH Clinical Center
Bethesda, Maryland 20892-2655
Toll-free: 800-411-1222
Fax: 301-480-9793
Web site:

You can find helpful general information on clinical trials at the following Web page.

A tutorial about clinical trials that can also help answer your questions can be found at the following link from the National Library of Medicine:

The Huntington Study Group (HSG) is a non-profit group of clinical investigators from medical centers in the United States, Canada, Europe, Australia, New Zealand and South America with experience in the care of patients and families affected by Huntington disease and dedicated to clinical research of this hereditary disorder. The HSG focuses on clinical research, including treatment trials and observational studies aimed at relieving the burden and slowing the progression of Huntington disease. See the Clinical Trials and Observational Studies in Progress for the current HSG trials.

The National Institute of Neurological Disorders and Stroke (NINDS), a part of the National Institutes of Health (NIH), has developed a brochure which presents information about Huntington disease and about current research progress. You can access this brochure online at the following link:

The NINDS has sponsored a Huntington Disease Research Roster at the Indiana University Medical Center in Indianapolis. This roster makes research possible by matching scientists with patient and family volunteers. The first DNA bank was established through the roster. Although the gene has already been located, DNA from individuals who have HD is still of great interest to investigators. Participation in the roster and in specific research projects is voluntary and confidential. For more information about the roster and DNA bank, contact:

Indiana University Medical Center
Department of Medical and Molecular Genetics
Medical Research and Library Building
975 W. Walnut Street
Indianapolis, IN 46202-5251
Phone: 317-274-5744

Resources on many charitable or special-fare flights to research and treatment sites and low-cost hospitality accommodations for outpatients and family members, as well as ambulance services, are listed on the Web site of the Office of Rare Diseases (ORD), part of the National Institutes of Health.

Last updated: 10/18/2013

Other Names for this Disease
  • HD
  • Huntington chorea
  • Huntington's chorea
  • Huntington's disease
See Disclaimer regarding information on this site. Some links on this page may take you to organizations outside of the National Institutes of Health.