Huntington's disease

Huntington's disease
Name	Huntington's disease
Synonyms	Huntington's chorea
Caption	A neuron with an inclusion (orange) caused by a mutated protein, a hallmark of the disease.
Field	Neurology, Psychiatry
Symptoms	Uncontrolled movements, emotional problems, loss of thinking ability
Complications	Pneumonia, Heart disease, Physical trauma from falls, Suicide
Onset	Typically 30–50 years old
Duration	Lifelong
Causes	Genetic (Autosomal dominant)
Risks	Having a parent with the condition
Diagnosis	Genetic testing
Differential	Neuroacanthocytosis, Dentatorubral-pallidoluysian atrophy, Wilson's disease
Prevention	Preimplantation genetic diagnosis
Treatment	Supportive care
Medication	Tetrabenazine, Antipsychotics, Antidepressants
Prognosis	Life expectancy ~15–20 years from symptom onset
Frequency	5–10 per 100,000 people of European descent

Huntington's disease. It is a rare, inherited neurodegenerative disorder that leads to the progressive breakdown of nerve cells in the brain. The condition is caused by a genetic defect on chromosome four and is characterized by a triad of motor, cognitive, and psychiatric symptoms. There is currently no cure, and management focuses on alleviating symptoms and providing supportive care.

Introduction

The disease is named after George Huntington, an American physician who provided a classic description of its hereditary nature in 1872. The underlying genetic cause was identified in 1993 by a collaborative research group, the Huntington's Disease Collaborative Research Group. The prevalence is highest among populations of Western European descent, particularly those with ancestry from the British Isles. The disorder has been depicted in various cultural works, such as the documentary The Lion's Mouth Opens and the novel Inside the O'Briens.

Causes

It is caused by an autosomal dominant mutation in the huntingtin (HTT) gene located on the short arm of chromosome 4. This mutation involves an unstable expansion of a CAG trinucleotide repeat within the gene's coding sequence. Individuals with more than 40 repeats will almost certainly develop the disorder, a phenomenon known as anticipation, where the repeat size can expand in successive generations. The mutant gene produces a misfolded protein that is toxic to neurons, particularly affecting the striatum and cerebral cortex of the basal ganglia.

Symptoms

Symptoms typically manifest between ages 30 and 50, though juvenile-onset forms exist. The most recognizable motor symptom is chorea—involuntary, jerky dance-like movements. Other motor signs include dystonia, bradykinesia, and impaired gait. Cognitive symptoms involve a decline in executive function, processing speed, and eventually dementia. Psychiatric manifestations are common and can include depression, apathy, obsessive-compulsive behaviors, and psychosis.

Diagnosis

Diagnosis is primarily confirmed through genetic testing to count the number of CAG repeats in the HTT gene. This is often preceded by a clinical neurological examination by a specialist in movement disorders. Imaging techniques like MRI or CT scans may show characteristic atrophy of the caudate nuclei. Differential diagnosis includes other conditions causing chorea, such as Sydenham's chorea, benign hereditary chorea, and neuroferritinopathy.

Management

Treatment is symptomatic and multidisciplinary, involving neurologists, psychiatrists, physical therapists, and speech therapists. The FDA has approved tetrabenazine and deutetrabenazine specifically to suppress chorea. Psychiatric symptoms may be managed with antidepressants like SSRIs or antipsychotics such as olanzapine. Nutritional support is critical due to swallowing difficulties, and advanced care planning often involves discussions with organizations like the Huntington's Disease Society of America.

Research

Active research directions include gene-silencing therapies, such as antisense oligonucleotides being investigated in trials by companies like Roche and Wave Life Sciences. Other approaches aim to reduce toxic protein aggregates or support neuronal survival through neurotrophic factors. International collaborative efforts like Enroll-HD and the European Huntington's Disease Network facilitate large-scale observational studies. Research into biomarkers is also a priority for groups like the CHDI Foundation.

Category:Genetic disorders Category:Neurodegenerative disorders Category:Rare diseases