Huntington’s disease is a neurodegenerative disorder characterized by uncontrolled movements, loss of cognitive ability, and psychiatric problems. It was first documented in 1872 by a 22-year-old American doctor named George Huntington.
An estimated 30,000 people in the United States have Huntington’s disease, which occurs in 2.7 per 100,000 inhabitants worldwide. In Europe, it affects 10 per every 100,000 people.
Causes of Huntington’s disease
The rare disorder is caused by a mutation in the huntingtin (HTT) gene, which provides the body’s cells with instructions to make the huntingtin protein. In this gene, there is a CAG repeat, a part of the genetic code where the DNA bases “CAG” are repeated, usually 10 to 35 times.
The mutation that causes Huntington’s is called a CAGÂ trinucleotide repeat expansion because the part of the gene with CAG repeats is longer than usual, often with 40 or more repeats. In general, people with a longer CAG repeat in the HTT gene have an earlier onset of symptoms, and their symptoms are usually more severe.
Every person inherits two copies of the HTT gene, one from each biological parent. Huntington’s is inherited in an autosomal dominant manner, meaning that a person only needs one copy of the mutated gene to develop the disease.
What happens in Huntington’s?
The CAG trinucleotide repeat expansion in the HTT gene leads to the production of an abnormally long huntingtin protein. It is thought that this abnormally long protein forms aggregates or clumps in the brain, which cause damage to various parts of the brain. However, the exact mechanisms by which mutant huntingtin protein leads to damage in the brain are still being explored.
Huntington’s is characterized by symptoms such as uncontrolled jerking and writhing movements known as chorea, walking difficulties, and problems with speech and swallowing. People with Huntington’s may experience cognitive impairment, and have difficulties in thinking, planning, and organizing. Emotional instability and behavioral changes also are common in individuals with Huntington’s.
The symptoms vary, both from person to person and within any one individual throughout the course of the disease. Progressive in nature, the disease symptoms get worse over time.
Disease types
Huntington’s symptoms typically appear during a person’s 30s and 40s. This is called adult-onset Huntington’s disease, and is the most common type.
The other type, accounting for about 5-10% of all cases, is juvenile Huntington’s disease (JHD), in which symptoms appear before the age of 20. This type of Huntington’s tends to progress more quickly than the adult form. Individuals with JHD frequently experience muscle stiffness and seizures instead of chorea, and about one in three JHD patients experiences seizures. In general, people with JHD have a longer CAG repeat expansion in their HTTÂ gene than those with the adult form.
Diagnosing the disease
Genetic testing for a mutation of the HTT gene can help doctors determine whether a person will develop the disease. Because Huntington’s usually progresses slowly, it is possible to test positive for the disease without experiencing symptoms.
A person who has one mutated copy of the HTT gene has a 50% chance of passing the disease-causing mutation to his or her biological children. Genetic counseling can help families with Huntington’s gene mutations make informed reproductive choices.
Managing Huntington’s
There is no cure for Huntington’s, nor are there any disease-modifying treatments that can alter its progression. Nonetheless, existing medications may help patients manage their symptoms and improve their quality of life. Examples of these treatments include medications to treat chorea, anticonvulsant drugs for seizures, and antidepressants for mood changes.
Researchers also are developing a number of experimental therapies for Huntington’s.
Non-drug therapies also can be helpful for people with Huntington’s. For example, physical therapy can help patients regain some control over their movements, while occupational therapy can make day-to-day tasks easier to manage. Speech therapy can aid with difficulty talking or swallowing, and palliative care can improve patients’ quality of life.
Last updated: June 11, 2021
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