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People with 36 to 39 CAG repeats may or may not develop the signs and symptoms of Huntington disease, while people with 40 or more repeats almost always develop the disorder.Īn increase in the size of the CAG segment leads to the production of an abnormally long version of the huntingtin protein. In people with Huntington disease, the CAG segment is repeated 36 to more than 120 times. Normally, the CAG segment is repeated 10 to 35 times within the gene.

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This segment is made up of a series of three DNA building blocks (cytosine, adenine, and guanine) that appear multiple times in a row. The HTT mutation that causes Huntington disease involves a DNA segment known as a CAG trinucleotide repeat. Although the function of this protein is unclear, it appears to play an important role in nerve cells (neurons) in the brain. The HTT gene provides instructions for making a protein called huntingtin. Mutations in the HTT gene cause Huntington disease. Juvenile Huntington disease tends to progress more quickly than the adult-onset form affected individuals usually live 10 to 15 years after signs and symptoms appear. Seizures occur in 30 percent to 50 percent of children with this condition. School performance declines as thinking and reasoning abilities become impaired. Additional signs of the juvenile form include slow movements, clumsiness, frequent falling, rigidity, slurred speech, and drooling. It also involves movement problems and mental and emotional changes. Individuals with the adult-onset form of Huntington disease usually live about 15 to 20 years after signs and symptoms begin.Ī less common form of Huntington disease known as the juvenile form begins in childhood or adolescence. People with this disorder also experience changes in personality and a decline in thinking and reasoning abilities.

Affected individuals may have trouble walking, speaking, and swallowing.

As the disease progresses, these movements become more pronounced. Many people with Huntington disease develop involuntary jerking or twitching movements known as chorea.

Early signs and symptoms can include irritability, depression, small involuntary movements, poor coordination, and trouble learning new information or making decisions. Huntington disease is a progressive brain disorder that causes uncontrolled movements, emotional problems, and loss of thinking ability (cognition).Īdult-onset Huntington disease, the most common form of this disorder, usually appears in a person's thirties or forties.

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