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Diseases

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
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Cause

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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

References
  1. Huntington disease. Genetics Home Reference. June, 2013; http://ghr.nlm.nih.gov/condition/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.