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Genetic and Rare Diseases Information Center (GARD)

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Huntington disease

Other Names for this Disease
  • HD
  • Huntington's chorea
  • Huntington's disease
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What causes Huntington disease?

Mutations in the HTT gene cause Huntington disease. The HTT gene provides instructions for making a protein called huntingtin. Although the function of this protein is unknown, it likely plays an important role in nerve cells.[1]

The type of mutation in the HTT gene that causes Huntington disease is called a CAG repeat expansion. CAG repeats are segments of DNA that are normally repeated 10 to 35 times. In people with Huntington disease the CAG segment is repeated 36 to more than 120 times. The abnormally expanded CAG segment leads to the production of a huntingtin protein that contains a long stretch of the amino acid glutamine. The elongated protein disrupts the normal function of nerve cells in certain parts of the brain, and ultimately leads to the death of those cells. The dysfunction and loss of nerve cells cause the signs and symptoms of Huntington disease.[1]
Last updated: 2/25/2010

  1. Huntington disease. Genetics Home Reference. 2013; Accessed 2/4/2014.