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Genetic and Rare Diseases Information Center (GARD)

Huntington disease

Other Names for this Disease
  • Huntington's chorea
  • Huntington's disease
  • HD
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 change (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.[1]

The HTT gene mutation that causes HD involves a DNA segment known as a CAG trinucleotide repeat. This segment is made up of three 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.[1]

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: 7/8/2015

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 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: 7/8/2015

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 substances) and CAG repeat expansion or Huntington disease. However, we identified 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.

, Mehta AJ, Yu CL. Genetic susceptibility to occupational exposures. Occup Environ Med. 2008 Jun;65(6):430-6; quiz 436, 397.

Last updated: 7/8/2015

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; alcohol; and smoking.[2] 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: 7/8/2015

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: 7/8/2015

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: 5/18/2016

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