Updated: 2/4/2020

Huntington Disease

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Snapshot
  • A 30-year-old woman presents with a two year history of anxiety, gait instability, and progressively worsening tics. She has no family history of neurologic disease, but her father committed suicide at age 32. MRI scan of the brain shows atrophy of the cerebral cortex and caudate nucleus.
Introduction
  • Definition
    • autosomal dominant, incurable neurodegenerative disorder characterized by choreiform movements, cognitive decline, mood dysfunction
  • Pathophysiology  
    • autosomal dominant CAG triplet repeat expansion in one allele of the HD (huntingtin) gene on chromosome 4 
    • number of CAG repeats determines presence of disease
      • < 29 repeats: no disease, or normal phenotype
      • 30-35 repeats: intermediate (no risk to the individual, but increased risk for offspring) allele
      • 36-39 repeats: incomplete penetrance allele
      • > 39 repeats: full penetrance allele
    • number of CAG repeats may increase with subsequent generations,(anticipation) particularly with paternal transmission
    • HD mutation results in neuronal death, particularly in the caudate nucleus and putamen (basal ganglia)
    • age of onset and severity of disease is inversely correlated with number of CAG repeats 
  • Epidemiology
    • usually begins between ages 30-50, but may begin as early as infancy (juvenile HD if age of onset < 20), or in older age
    • both sexes are affected equally
Presentation
  • Symptoms
    • involuntary movements
      • chorea, or choreiform movements (dancelike hyperkinetic movements)
      • athetotic (or choreathetotic) movements
      • tics or grimacing
      • ataxia
      • falls 
    • cognitive deterioration
      • memory loss
      • language disability
    • psychiatric dysfunction
      • depression
      • suicidal ideation and suicide
      • irritability and anxiety
      • psychosis
      • sleep disturbance
      • aggresivity or impulsivity
      • substance abuse
      • hyper or hyposexuality
    • other symptoms
      • weight loss
      • swallowing difficulty and aspiration
Evaluation
  • Labs
    • molecular genetic testing for number of CAG repeats in each of the HD alleles is diagnostic 
  • Imaging 
    • MRI shows atrophy of caudate and putamen, as well as general cerebral atrophy  
Differential
  • Tourette's (Tic) disorder
  • Syndenham chorea
  • Schizophrenia 
  • Tardive dyskinesia
  • Wilson's disease
  • Spinocerebellar ataxia
Treatment
  • No curative treatment or treatment altering disease progression
  • Supportive treatment can be highly effective
    • reserpine, tetrabenazine, or atypical antipsychotics for involuntary movements
    • SSRIs for depression
    • atypical antipsychotics for psychosis and behavior problems
    • benzodiazepines for sleep disturbance
  • Genetic counseling should be offered for patients, family members, and at-risk offspring
Prognosis, Prevention, and Complications
  • Condition is inevitably fatal
  • Average prognosis is approximately 20 years from symptom onset
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