Huntington’s disease is an inherited disease that causes the progressive breakdown (degeneration) of nerve cells in the brain. Huntington’s disease has a broad impact on a person’s functional abilities and usually results in movement, thinking (cognitive) and psychiatric disorders.
Most people with Huntington’s disease develop signs and symptoms in their 40s or 50s, but the onset of disease may be earlier or later in life. When disease onset begins before age 20, the condition is called juvenile Huntington’s disease. Earlier onset often results in a somewhat different presentation of symptoms and faster disease progression.
Huntington’s disease is caused by a genetic defect on chromosome 4. The defect causes a part of DNA, called a CAG repeat, to occur many more times than it is supposed to. Normally, this section of DNA is repeated 10 to 28 times. But in persons with Huntington’s disease, it is repeated 36 to 120 times.
As the gene is passed down through families, the number of repeats tend to get larger. The larger the number of repeats, the greater your chance of developing symptoms at an earlier age. Therefore, as the disease is passed along in families, symptoms develop at younger and younger ages.
There are two forms of Huntington’s disease. The most common is adult-onset Huntington’s disease; people with this form of the disease usually develop symptoms in their mid 30s and 40s. An early-onset form of Huntington’s disease accounts for a small number of cases and is generally diagnosed in childhood or adolescence.
The movement disorders associated with Huntington’s disease can include both voluntary and involuntary movements, often with significant impairment:
- Involuntary jerking or writhing movements (chorea)
- Involuntary, sustained contracture of muscles (dystonia)
- Muscle rigidity or stiffness
- Slow, uncoordinated fine movements
- Slow or abnormal eye movements
- Impaired gait, posture and balance
- Difficulty with the physical production of speech
- Difficulty swallowing
Impairments in voluntary movements — rather than the involuntary movements — may have a greater impact on a person’s ability to work, perform daily activities, communicate and remain independent.
Cognitive impairments often associated with Huntington’s disease include:
- Difficulty planning, organizing and prioritizing tasks
- Inability to start a task or conversation
- The tendency to get stuck on a thought, behavior or action (perseveration)
- Lack of impulse control that can result in outbursts, acting without thinking and sexual promiscuity
- Problems with spatial perception that can result in falls, clumsiness or accidents
- Lack of awareness of one’s own behaviors and abilities
- Difficulty focusing on a task for long periods
- Slowness in processing thoughts or “finding” words
- Difficulty in learning new information
The most common psychiatric disorder associated with Huntington’s disease is depression. This isn’t simply a reaction to receiving a diagnosis of Huntington’s disease. Instead, depression appears to occur because of injury to the brain and subsequent changes in brain function.
There is no cure for Huntington’s disease, and there is no known way to stop the disease from getting worse. The goal of treatment is to slow down the symptoms and help the person function for as long and as comfortably as possible. Depression and suicide are common among persons with Huntington’s disease. It is important for all those who care for a person with Huntington’s disease to monitor for symptoms and treat accordingly.
As the disease progresses, the person will need assistance and supervision, and may eventually need 24-hour care.