Huntington’s disease is a neurodegenerative disorder characterized by symptoms such as uncontrolled movements, loss of thinking ability, and psychiatric problems.
The disease is caused by a mutation of the huntingtin (HTT) gene. The mutation is called a CAG trinucleotide repeat expansion, because a segment of the gene containing repeats of the sequence “CAG” is longer than normal. The longer this repeat region is, the earlier and more severe the symptoms tend to be.
Movement disorders
One of the most common movement problems in people with Huntington’s is chorea. This term comes from the ancient Greek word “choreia,” which means dance. Chorea is characterized by brief and abrupt movements that are irregular and unpredictable.
These movements often seem to flow from one body part to another, but they can also be confined to a single area in the body. They can interfere with swallowing, speech, posture, and walking. Chorea often leads to clumsiness, which causes the person to drop objects repeatedly. People who are unfamiliar with chorea also describe the movements as restlessness or fidgeting.
Chorea usually occurs during the early intermediate stage of the disease, several years after disease onset, and diminishes at advanced stages of the disease, at which time dystonia — involuntary muscle contractions — emerges.
People with Huntington’s may also experience abnormal slowness of movement (bradykinesia). Difficulties with balance and walking also can occur.
A lack of motor control can also make it difficult to speak, and can cause problems with eating and swallowing, thereby making weight loss a common feature of the disease.
Cognitive, behavioral, and psychiatric problems
Because Huntington’s causes the deterioration and death of cells in certain areas of the brain, and each area is linked to one or a handful of behaviors, the disease often leads to changes in behavior.
One brain region called the caudate nucleus, thought of as the brain’s information processing center, is where the heaviest nerve damage occurs in Huntington’s. In addition to being involved in the control of voluntary movement, the caudate nucleus organizes and regulates information it receives from other parts of the brain, and then sends the information on to the frontal lobes, which are the executive or command center for many cognitive functions.
As such, cognitive impairment is common in people with Huntington’s, and is often detectable before the onset of other symptoms.
People with Huntington’s may experience a range of psychiatric and emotional problems, such as apathy (a loss of motivation), anxiety, and depression. Other psychiatric issues, ranging from obsessive-compulsive disorder to psychosis, can also occur. In psychosis, which affects as many as one out of every 10 patients, a person experiences hallucinations (seeing, hearing, or otherwise sensing things that aren’t there) and/or delusions (fixed beliefs without any basis in reality).
People with Huntington’s commonly have difficulty regulating their emotions, which can cause outbursts of irritability and anger. The disease can cause disinhibition — meaning a person may lose the ability to filter their thoughts, saying or doing things that are not socially appropriate.
Additional symptoms
Cognitive and emotional changes may make communication difficult. Patients may have difficulty focusing on conversations and translating their thoughts into words. Communication difficulties are often exacerbated by a loss of coordination in the throat muscles, which can make speech difficult.
The combination of emotional difficulties and physical symptoms can lead to issues with sexuality. Across genders, more than three out of every four Huntington’s patients report difficulties in their sexual relations. Patients commonly experience a lack of interest in sex. Less commonly, some individuals will experience an increased sex drive that can lead to inappropriate or risky sexual behavior.
Last updated: July 12, 2021
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