September 2018 By PsychDB.com

Huntington's Disease (HD)

Huntington's Disease (HD) is a hereditary, neurodegenerative illness characterized by a triad of symptoms including motor disturbance, cognitive impairment, and psychiatric features.

Prevalence

The worldwide prevalence is estimated to be 2.7 per 100,000. The prevalence of Huntington's disease in North America, Europe, and Australia is 5.7 per 100,000. The prevalence is much lower in Asia, and is 0.40 per 100,000. The average age at diagnosis of Huntington's disease is approximately 40 years, although this varies widely. Age at onset is inversely correlated with CAG expansion length.

Psychiatric and cognitive abnormalities can predate the motor abnormality by at least 15 years. Initial symptoms requiring care often include irritability, anxiety, or depressed mood. Other behavioural disturbances may include pronounced apathy, disinhibition, impulsivity, and impaired insight, with apathy often becoming more progressive over time.

Criterion A

The criteria are met for major or mild neurocognitive disorder.

Criterion B

There is insidious onset and gradual progression.

Criterion C

There is clinically established Huntington’s disease, or risk for Huntington’s disease based on family history or genetic testing.

Criterion D

The neurocognitive disorder is not attributable to another medical condition and is not better explained by another mental disorder.

Progressive cognitive impairment is a core feature of Huntington's disease, with early changes in executive function (i.e. - processing speed, organization, and planning) rather than learning and memory. Cognitive and associated behavioural changes often precede the emergence of the typical motor abnormalities of bradykinesia (i.e., slowing of voluntary movement) and chorea (i.e., involuntary jerking movements).

A diagnosis of definite Huntington's disease is given in the presence of unequivocal, extrapyramidal motor abnormalities in an individual with either a family history of Huntington's disease or genetic testing showing a CAG trinucleotide repeat expansion in the huntingtin (HIT) gene, located on chromosome 4.