Huntington’s disease is a genetic brain disorder that progressively destroys nerve cells, causing a combination of uncontrollable movements, cognitive decline, and psychiatric symptoms. It affects roughly 5 to 9 people per 100,000 in European and North American populations, and symptoms typically appear between the ages of 30 and 50. The disease is always inherited, always progressive, and currently has no cure.
What Causes Huntington’s Disease
Huntington’s disease is caused by a mutation in a single gene called HTT, located on chromosome 4. Inside this gene, a short sequence of DNA building blocks (cytosine, adenine, guanine, abbreviated CAG) repeats itself over and over. In a healthy gene, this segment repeats 10 to 35 times. In someone with Huntington’s, it repeats 36 to more than 120 times.
The number of repeats matters. People with 40 or more CAG repeats almost always develop the disease. Those with 36 to 39 repeats fall into a gray zone: they may or may not develop symptoms in their lifetime. The expanded gene produces an abnormal form of the huntingtin protein, which gradually damages and kills neurons in specific regions of the brain.
The damage hits the basal ganglia hardest, particularly structures called the caudate and putamen. These areas are deeply involved in coordinating movement, regulating emotions, and filtering thoughts. Brain imaging studies show that this shrinkage begins years, sometimes over a decade, before a person notices any symptoms. Other brain regions degenerate too, but more slowly.
How It’s Inherited
Huntington’s follows an autosomal dominant inheritance pattern, which means you only need one copy of the mutated gene to develop the disease. If one of your parents carries the mutation, you have a 50 percent chance of inheriting it. Gender doesn’t matter, and there are no carriers who silently pass it along without risk to themselves. If you didn’t inherit the expanded gene, you can’t pass it to your children.
One complicating factor is that the number of CAG repeats can expand from one generation to the next, particularly when the gene is passed from a father. This means a parent with a borderline repeat count could have a child with a higher count and more severe disease. This phenomenon also explains juvenile-onset cases, which tend to involve very high repeat numbers.
Symptoms in Adults
Huntington’s disease affects three broad areas: movement, thinking, and mental health. These symptoms don’t all arrive at once. Many people first notice subtle changes in mood or coordination years before a formal diagnosis.
The hallmark movement symptom is chorea, involuntary jerking or writhing movements that can affect the arms, legs, face, and tongue. Early on, these movements may look like fidgeting or restlessness. Over time, they become more pronounced and harder to conceal. Alongside chorea, people often develop muscle rigidity, difficulty walking, problems with balance, slow or abnormal eye movements, and trouble swallowing or speaking clearly.
Cognitive symptoms tend to creep in gradually. You might struggle to organize tasks, stay focused, or shift between activities. Thinking becomes less flexible, and impulse control can weaken, leading to outbursts or poor decision-making. These changes can be especially frustrating because the person is often aware of them, at least in the early and middle stages.
Psychiatric symptoms are common and sometimes appear before any movement problems. Depression, irritability, anxiety, and apathy are frequently reported. Some people experience obsessive-compulsive behaviors or social withdrawal. These psychiatric changes can be mistaken for other conditions, delaying the recognition that Huntington’s may be the underlying cause.
Juvenile Huntington’s Disease
When symptoms begin at age 20 or younger, the condition is classified as juvenile Huntington’s disease. It accounts for a small percentage of all cases but tends to progress faster, with a typical disease duration of 10 to 15 years after symptoms appear.
Juvenile Huntington’s looks different from the adult form. Chorea is uncommon in children under 10. Instead, the earliest signs are often speech difficulties, problems with fine motor coordination, and gait disturbances. Rigidity, slowness of movement, and dystonia (sustained muscle contractions) are prominent, especially in very young children. Seizures occur in a significant number of cases, which is rare in adult-onset Huntington’s. Spasticity may be present in over 70 percent of juvenile cases, and cerebellar ataxia (a type of unsteadiness) affects up to 35 percent.
Interestingly, cognitive function tends to be better preserved in juvenile cases compared to adults, though behavioral symptoms like irritability and aggression can be severe. These behavioral changes are sometimes mistaken for autism spectrum disorder or ADHD, which can delay the correct diagnosis.
How It’s Diagnosed
Diagnosis typically starts with a neurological exam covering motor function, sensory responses, and psychiatric symptoms. A neurologist will test reflexes, muscle strength, balance, and coordination, along with assessing mood and mental status. Neuropsychological testing may follow, evaluating memory, reasoning, language, and spatial skills to map the extent of cognitive involvement.
Brain imaging with MRI or CT can reveal the characteristic shrinkage of the basal ganglia, which supports the clinical picture. But the definitive test is genetic. A blood sample is analyzed for the number of CAG repeats in the HTT gene, and a count of 40 or above confirms the diagnosis.
For people who have a parent with Huntington’s but no symptoms of their own, predictive genetic testing is available. This is a significant decision. A positive result means you will almost certainly develop the disease at some point, and there’s currently no way to prevent it. Because of this, predictive testing is only performed after consultation with a genetic counselor, who walks through the implications, inheritance patterns, and emotional weight of the results before any blood is drawn.
Disease Progression and Life Expectancy
Huntington’s is divided into early, middle, and late stages, though the boundaries between them aren’t sharp. In the early stage, people can generally live independently, though they may need help with complex tasks. Chorea is present but manageable, and cognitive changes are mild. In the middle stage, chorea typically worsens, daily tasks become harder, and falls are more frequent. Swallowing difficulties begin to emerge, and thinking slows noticeably.
In the late stage, people require full-time care. Chorea may actually decrease as the muscles become more rigid, but voluntary movement becomes severely limited. Communication is difficult, and swallowing problems raise the risk of choking and pneumonia, which are common causes of death. The time from first symptoms to death is typically 10 to 30 years, with significant variation depending on the individual and their CAG repeat length.
Treatment and Symptom Management
No treatment can slow or stop Huntington’s disease. Current management focuses entirely on easing symptoms and maintaining quality of life for as long as possible.
For chorea, medications that reduce dopamine activity in the brain are the primary option. These drugs work by limiting the chemical signaling that drives involuntary movements. They don’t eliminate chorea entirely, but they can reduce it enough to improve daily functioning, make eating safer, and reduce the risk of injury. Side effects can include drowsiness, depression, and restlessness, so the balance between benefit and burden requires ongoing adjustment.
Depression and anxiety are treated with standard psychiatric medications. Physical therapy helps maintain mobility and reduce fall risk. Speech therapy addresses communication and swallowing difficulties, and occupational therapy helps people adapt their homes and routines as their abilities change. Nutritional support becomes increasingly important as the disease progresses, because the combination of constant involuntary movement and swallowing problems can lead to dangerous weight loss.
Who Is Most Affected
Huntington’s disease occurs worldwide, but prevalence varies strikingly by region. A large meta-analysis found the global pooled prevalence is about 4.88 per 100,000 people. Europe and North America have the highest rates, at roughly 6 to 9 per 100,000. Oceania shows similar numbers. In contrast, prevalence in Asia is around 1 per 100,000, and in Africa it drops to approximately 0.25 per 100,000. These differences are thought to reflect the historical frequency of the expanded HTT gene in populations of European descent.