Huntington disease

Overview

Huntington disease is a progressive disorder of neurons in brain networks that control movement, executive function, mood and behavior. The genetic cause is an expanded CAG trinucleotide repeat in HTT; the expansion produces an abnormal huntingtin protein and, over years, characteristic degeneration of the striatum and connected cortical circuits. ^{[1] [2]}

The disorder is autosomal dominant, so one pathogenic HTT allele is sufficient to cause disease. Larger CAG expansions are generally associated with earlier onset, although repeat size does not precisely predict an individual course. Repeat length can expand between generations, particularly through paternal transmission, contributing to anticipation in some families. ^{[1] [2]}

Symptoms commonly begin between ages 30 and 50, but onset ranges widely. Depression, irritability, apathy, impaired judgment and subtle cognitive change can appear before obvious motor abnormalities. As disease progresses, chorea may coexist with rigidity, dystonia, swallowing difficulty and loss of independence. ^{[1] [2] [3]}

Symptoms and warning signs

Motor symptoms include chorea, clumsiness, abnormal eye movements, impaired balance, dystonia, slurred speech and later difficulty swallowing. Cognitive symptoms affect planning, flexibility, attention and processing speed. Psychiatric symptoms can include depression, anxiety, irritability, compulsive behavior, apathy and, less commonly, psychosis. ^{[1] [2]}

Suicidal thoughts, severe behavioral crisis, choking, aspiration, repeated falls or sudden inability to manage basic needs require urgent assessment. New acute neurologic symptoms should not automatically be attributed to Huntington disease because stroke, infection, medication toxicity and other treatable problems still occur. ^{[1] [2]}

Diagnosis

Diagnosis combines a compatible neurologic syndrome and family history with molecular testing of the HTT CAG repeat. A neurologic examination assesses eye movements, tone, involuntary movements, gait and coordination, while cognitive and psychiatric assessment establishes the broader functional impact. ^{[1] [2]}

Genetic testing in a symptomatic patient can confirm the diagnosis. Predictive testing of an asymptomatic adult at 50% risk is a separate process and should include pretest counseling, informed consent and a plan for communicating results and psychological support. Testing minors who are asymptomatic is generally avoided unless there is a medical reason related to juvenile-onset disease. ^{[1] [2] [3]}

Other causes of chorea and behavioral change include medication effects, autoimmune disease, thyroid disorders, Wilson disease, structural brain disease and other inherited movement disorders. A negative or intermediate HTT result in an atypical syndrome should prompt evaluation for these alternatives. ^{[2] [3]}

Causes, risk factors and clinical context

The major risk factor is having a biological parent with Huntington disease or a pathogenic HTT expansion. Each child of an affected heterozygous parent has a 50% chance of inheriting the expansion. A negative family history does not fully exclude disease because relatives may have died before symptoms, been misdiagnosed or had unknown genetic status. ^{[1] [2]}

HD is progressive over many years. Early disease may allow independent work and family life with accommodations; middle stages bring increasing motor, cognitive and behavioral disability; advanced disease usually requires substantial assistance with feeding, mobility and personal care. ^{[1] [2] [3]}

Complications and why the diagnosis matters

Aspiration pneumonia, falls, weight loss, immobility, communication difficulty and psychiatric crises are major complications. Suicide risk is elevated compared with the general population and should be assessed directly rather than inferred from appearance or behavior. ^{[1] [2]}

There is currently no cure that stops neurodegeneration, but symptom treatment and coordinated supportive care can preserve quality of life and function. Course and survival vary, so care planning should be individualized rather than based on a fixed timeline. ^{[1] [2] [3]}

Treatment and management

Treatment is symptom specific. Vesicular monoamine transporter inhibitors such as tetrabenazine or deutetrabenazine can reduce troublesome chorea in selected patients, while antipsychotic, antidepressant or mood-stabilizing medicines are used when psychiatric symptoms warrant them. Medication choice must account for depression, sedation, swallowing risk and other adverse effects. ^{[1] [2]}

Physical, occupational and speech-language therapy address balance, daily activities, communication and swallowing. Nutrition support is often needed because involuntary movement and dysphagia contribute to weight loss. Social work, driving assessment, advance care planning and caregiver support are integral parts of treatment rather than optional extras. ^{[1] [2] [3]}

Drugs that reduce chorea can worsen depression, parkinsonism, sedation or swallowing in some patients. Behavioral changes should not automatically be treated with escalating sedatives; clinicians first consider pain, infection, environmental stress and medication effects. ^{[1] [2]}

Follow-up, recovery and prevention

Follow-up tracks motor symptoms, mood, cognition, swallowing, weight, falls, driving and caregiver burden. Needs evolve continuously, so a stable medication list does not mean the care plan is stable. Regular reassessment can identify treatable complications before they become crises. ^{[1] [2]}

The genetic condition cannot be prevented in someone who inherited the expansion, but reproductive options—including preimplantation genetic testing and prenatal testing—can be discussed with a genetics team. These are personal choices and require nondirective counseling. ^{[1] [2] [3]}

Special situations and care pathway

Juvenile HD often presents with rigidity, slowed movement, school decline and seizures rather than classic adult chorea. Predictive testing in asymptomatic adults has implications for mental health, insurance and family relationships, so counseling and privacy considerations are central. ^{[1] [2] [3]}

The pathway is neurologic diagnosis and genetic confirmation, baseline cognitive and psychiatric assessment, multidisciplinary symptom management, proactive swallowing and nutrition review, and repeated planning for safety and future care needs. ^{[1] [2]}

When to seek urgent medical care

Urgent help is needed for suicidal intent, severe agitation or psychosis creating danger, repeated choking or aspiration, sudden inability to swallow, or acute neurologic change that might represent another medical emergency. ^{[1] [2]}

Sources

1. National Institute of Neurological Disorders and Stroke — Huntington’s Disease: Hope Through Research
2. GeneReviews / NCBI Bookshelf — Huntington Disease
3. MedlinePlus Genetics — Huntington disease

This article is based on trusted medical sources and is awaiting clinician review. It is not a substitute for personalized medical advice.