Huntington’s Disease

Incidence: ~1/20000 (UK 300 cases/yr)

This is an autosomal dominant disease with age-dependent penetrance (i.e. age plays a role too- the mutation is more likely to have an effect the older you are), caused by CAG repeats in the Huntington gene.  It is a progressive neurodegenerative disorder characterised by atrophy of the caudate nucleus and putamen (known together as the corpus striatum).  Specifically, changes in neurotransmitter patters (Low ACh; Low GABA; Normal Dopamine).

This causes a gradual onset and progression of motor, cognitive and personality changes, usually starting between 30-50 years old.  Mortality is usually 20 years post diagnosis, by which time patients are usually severely dependent and disabled.

Motor Symptoms

Early symptoms include:

  • restlessness, twitching and a desire to move.
  • Handwriting and hand-eye coordination may decline.

Later symptoms include

  • Dystonia : sustained abnormal postures, rigidity (loss of movement)
  • Chorea: involuntary jerking/writhing/twisting (gain of movement)
  • Slowness of voluntary movement/inability to control the speed/force/initiation of movement
  • Dysarthria/dysphagia
  • Localised/generalised weakness, and impaired balance.

NB Notice the conflicting symptom pattern of dystonia and chorea. (see below)

Cognitive symptoms

  • Loss of ability to plan and execute routine tasks
  • Slowed thought
  • impaired/inappropriate judgement
  • Short-term memory loss

NB Long-term memory and recognition of surroundings is usually retained.

Personality/Behavioural/Other

  • Depression, irritability, anxiety, apathy, impulsivity, aggression
  • Social withdrawal
  • Metabolic disturbances (fairly new in the field)

Genetic testing will usually support the clinical diagnosis.

Treatment is largely supportive but phenothiazines e.g. sulpiride & tetrabenazine, may reduce the chorea by reducing the levels of dopamine in the brain.  NB this only really helps the early chorea-based symptoms, but will actually worsen the dystonic symptoms that come later as dopamine levels are depleted.  Early personality changes may also respond to drugs e.g. depression/antidepressants.

Occupational and Physio- therapies are very important.

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