Huntington’s disease is a genetic brain disorder that progressively destroys nerve cells, causing a combination of uncontrolled movements, cognitive decline, and psychiatric changes. It affects roughly 5 people per 100,000 worldwide, and there is currently no cure. The disease is caused by a single faulty gene inherited from a parent, and each child of someone carrying that gene has a 50% chance of inheriting it.
The Genetic Cause
Huntington’s disease is caused by a mutation in the HTT gene, which contains a repeating segment of DNA called a CAG trinucleotide repeat. In most people, this segment repeats 10 to 35 times. In people with Huntington’s, it repeats 36 to more than 120 times. People with 40 or more repeats almost always develop the disease. Those in the 36 to 39 range may or may not, which creates a gray zone of uncertainty for some families.
There’s also an intermediate range worth knowing about. People with 27 to 35 repeats won’t develop Huntington’s themselves, but the repeat count can expand when passed to children. This means their offspring could end up in the disease-causing range, which is why the condition can appear to strike a family with no prior history.
The disease follows an autosomal dominant inheritance pattern, meaning you only need one copy of the mutated gene to develop it. If one of your parents carries the mutation, you have a 50/50 chance of inheriting it at conception.
What Happens in the Brain
The mutated gene produces an abnormal version of a protein called huntingtin. This misshapen protein sets off a cascade of damage inside brain cells, particularly in a region called the striatum that helps coordinate movement, emotions, and thinking. The damage happens through several overlapping mechanisms.
One major problem is that the abnormal protein disrupts how cells produce energy. It interacts directly with the outer membrane of mitochondria, the structures that power your cells, causing them to malfunction and fragment. At the same time, it interferes with the cell’s internal transport system. Brain cells rely on long extensions called axons to shuttle essential materials from one end of the cell to the other. The mutant protein blocks this highway, preventing critical cargo like receptors and growth factors from reaching their destinations.
The striatum is especially vulnerable because its neurons depend on a survival signal produced in the cortex, a growth factor that supports their health. The mutant protein impairs both the production and the delivery of this signal, essentially starving these neurons of what they need to stay alive. On top of that, the affected neurons become overly sensitive to normal chemical signals from neighboring cells, a process that leads to toxic overstimulation and, eventually, cell death.
Movement Symptoms
The most recognizable feature of Huntington’s is chorea: involuntary, dance-like movements that can affect the fingers, feet, face, or torso. These movements tend to worsen when you’re anxious or distracted, and they become more pronounced as the disease progresses. Over time, chorea can make walking difficult and increase the risk of falls.
Not everyone with Huntington’s develops chorea. Some people instead become rigid and move very little, a condition called akinesia. Others start with chorea and gradually shift toward stiffness as the disease advances. Some develop dystonia, where muscles lock into unusual fixed postures. Tremor and abnormal eye movements are also common. The movement picture can look quite different from one person to the next.
Cognitive Changes
Cognitive decline in Huntington’s often begins subtly, years before a formal diagnosis. One of the earliest signs is a slowdown in thinking speed. Everyday mental tasks start taking longer and feel more exhausting than they used to. This change can be easy to dismiss as stress or aging, but it tends to be measurable on neuropsychological tests well before other symptoms appear.
As the disease progresses, it broadly affects executive function: the ability to plan, organize, switch between tasks, and make decisions. Memory is also impaired, though in a different way than Alzheimer’s. People with Huntington’s struggle more with learning new information and recalling it on demand, while their ability to recognize familiar things often stays relatively intact longer. Language difficulties emerge too, particularly with speaking clearly, initiating conversation, and organizing thoughts.
One of the more surprising early changes involves reading emotions. People in the earliest stages of Huntington’s often have trouble identifying emotions from facial expressions or tone of voice, with disgust and anger being the hardest to recognize. Sense of smell is affected in a similar way: you can detect that a smell is present but can’t identify what it is. About a third of people with Huntington’s also develop reduced awareness of their own symptoms and behaviors, which can create friction with caregivers and family members who see changes the person themselves doesn’t recognize.
Psychiatric and Behavioral Symptoms
Depression, anxiety, and apathy are common throughout the course of Huntington’s, and they can appear years before any movement problems. Irritability and anger are particularly frequent and can be among the most disruptive symptoms for families. Some people develop obsessive or compulsive behaviors, repeating actions or becoming fixated on specific routines.
These psychiatric changes are not simply a reaction to having a serious diagnosis. They’re a direct result of the same brain damage that causes the movement and cognitive symptoms. Together, the motor, cognitive, and psychiatric features form what clinicians call the triad of Huntington’s disease, and for many families, the behavioral and emotional changes are actually harder to manage day to day than the physical ones.
How Huntington’s Is Diagnosed
Diagnosis involves genetic testing to count the number of CAG repeats in the HTT gene. A result of 40 or more repeats confirms the diagnosis. For people who are at risk but don’t yet have symptoms, this is called predictive testing, and it comes with a structured process designed to ensure you’re prepared for the result.
Current guidelines, revised in 2016 by the Huntington’s Disease Society of America, require a minimum of two in-person appointments. The first includes genetic counseling, a mental health assessment, a neurological exam, informed consent, and a blood draw. The second appointment is the return of results. You can choose whether to bring a support person and whether to include a neurological evaluation, but the genetic counseling component is considered essential.
During counseling, you’ll discuss your family’s experience with the disease, your reasons for wanting to test, and how you might handle different outcomes. The counselor may also discuss the concept of anticipation, where CAG repeat length can expand across generations, potentially causing earlier onset in children than in their parents. Testing of minors is generally avoided, and testing may be delayed if someone is experiencing active psychiatric symptoms that need to be stabilized first.
Disease Progression
Huntington’s is a progressive disease, and its course is measured along a continuum. A newer framework called the HD Integrated Staging System breaks progression into stages starting from the moment a genetic expansion is identified (stage 0), through early brain changes visible on imaging (stage 1), to measurable cognitive and motor decline (stage 2), and finally to loss of independence in daily activities (stage 3). Symptoms typically appear between ages 30 and 50, though this varies. Most people live 15 to 20 years after the onset of symptoms.
The rate of progression differs from person to person, but the general trajectory moves from subtle cognitive and mood changes, to more obvious movement problems and functional decline, to a late stage where full-time care is needed. The number of CAG repeats influences onset: higher repeat counts tend to produce earlier symptoms.
Juvenile Huntington’s Disease
About 5 to 10% of Huntington’s cases begin before age 20. This form, called juvenile Huntington’s disease, looks quite different from the adult version. Rather than chorea, children and adolescents are more likely to develop rigidity, slow movement, seizures, and problems with coordination and balance. Behavioral changes like irritability and hyperactivity are common early signs. The juvenile form tends to progress faster than adult-onset Huntington’s and is usually inherited from the father, whose sperm cells are more prone to expanding the CAG repeat count during reproduction.
Treatment and Symptom Management
There is no treatment that slows or stops Huntington’s disease. Current management focuses entirely on reducing symptoms. For chorea, the primary option is a medication called tetrabenazine, which works by reducing the activity of a brain chemical involved in movement. It can be effective but carries significant side effects, including depression and suicidal thoughts, so it requires careful monitoring.
Antipsychotic medications are frequently used to manage both movement symptoms and behavioral problems like agitation and irritability. Antidepressants, particularly from the SSRI class, are commonly prescribed for the depression and anxiety that accompany the disease. Beyond medication, physical therapy helps maintain mobility and reduce fall risk, speech therapy addresses communication and swallowing difficulties, and occupational therapy helps people adapt their daily routines as their abilities change.
For many families, the most important support is practical: help with caregiving logistics, access to mental health services for both the person with Huntington’s and their family members, and connection to organizations like the Huntington’s Disease Society of America that can provide resources throughout the course of the disease.