11th August 2024

Huntington’s disease

Huntington’s is a neurodegenerative condition resulting in a choreiform movement disorder, impaired cognition and emotional/behavioural disturbance. It has autosomal dominant inheritance due to an abnormally long triplet ‘CAG’ repeat in the huntingtin gene on chromosome 4. Disease usually occurs in middle age, age 40-60 years, but onset can be much earlier or later than this. With successive generations there is a risk of elongation of the CAG repeat length, resulting in earlier symptom onset (anticipation). This is much more common when the gene is transmitted through the paternal line.

Clinical onset is insidious, and subtle cognitive and behavioural changes often predate the onset of motor symptoms by a decade or more, but may not be recognised. The defining movement abnormality is chorea, Latin for ‘dance’, characterised by sudden, uncontrollable and involuntary jerking movements of the limbs or face, which may make the patient appear to be dancing or fidgeting.  The more severe form is ballism, in which the movements are quite violent and can be distressing for the patient, sometimes resulting in injuries to the patient or others in the vicinity.

Huntingdon’s is a clinical diagnosis although genetic testing can be useful if there is uncertainty such as in de novo cases with no family history. Brain atrophy is prominent and occurs earliest in the caudate nucleus and putamen, with cortical involvement as the condition advances.

Unfortunately, there is currently no way to prevent disease progression, so treatment aims to manage symptoms. Anti-dopaminergic drugs such as tetrabenazine or antipsychotics can be used for movement disorders including chorea. A variety of standard psychiatric drugs are used to treat the behavioural impairments including antidepressants, in particular SSRIs and other mood-stabilising drugs such as valproate or carbamazepine for the irritability. There are no pharmacological options for the cognitive impairment. As the disease progresses, physiotherapy, occupational therapy and speech therapy input are very helpful, and affected individuals may eventually need a wheelchair or be bed bound and need full-time care due to the combination of motor and cognitive impairment.