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.
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
- Localised/generalised weakness, and impaired balance.
NB Notice the conflicting symptom pattern of dystonia and chorea. (see below)
- 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.
- 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.