Overview

Huntington’s disease (HD) is a degenerative genetic disorder that typically begins in early to middle adulthood. There are some HD cases that begin in early childhood and adolescence. Individuals with HD experience a variety of symptoms, including motor, cognitive, and psychiatric disturbances. In the early stages of the disorder, an individual is able to perform daily tasks without any problems. However, as the disorder progresses, symptoms will worsen. There is currently no cure for the disease, and death occurs within 15 to 20 years (1).

Typology

There are two main types of HD: juvenile-onset and adult-onset. Juvenile-onset HD is associated with onset under the age of 21. Adult-onset HD is associated with onset during early and middle adulthood. A small percentage of adults may experience disease onset after the age of 60 (termed late-onset). Juvenile-onset HD is characterized by rapid symptom progression and is relatively rare (only 3.5% to 6% out of all HD cases). In contrast, adult-onset HD is characterized by a more gradual progression of symptoms (1).

Symptoms

In the early stages of the disorder, a patient with HD will have no problems in performing daily activities. However, as the disease progresses, motor, cognitive and psychological symptoms become apparent. Motor symptoms may include involuntary movements, such as irregular jerking or writhing movements involving the limb, trunk, and face (chorea). In addition, some patients may have problems with muscle (dystonia), eye movements, balance (impaired gait and posture), speech, and/or swallowing (1).

Cognitive impairments are commonly associated with HD. For juvenile cases, this can include intellectual disabilities. Children and adolescents who are diagnosed with HD show difficulty with organization and completion of assigned tasks. Moreover, they can become fixated on particular thoughts and behaviors. In some situations, there is a lack of impulse control and behavioral regulation, which can result in tantrums and outbursts. Cognitive impairments can also be present in adults and are often associated with a “sub-cortical” syndrome. This syndrome consists of cognitive impairments in learning, attention, inhibition, and anticipation of future consequences. In lacking these skills, patients are unable to process and recall information. Their attention and working memory deficits reduce their ability to perform tasks which require divided attention, such as driving a car while listening to the radio (1).

Psychiatric symptoms are often present in patients with HD (up to 79%) (2). Common psychiatric symptoms include depression, suicidal ideation, social withdrawal, irritability, aggression, obsessions, delusions, hallucinations, insomnia, and fatigue (1,2). In some severe cases, suicide may occur. Suicide is more common in HD than any other neurological disorder (3).

Course

The progression of HD varies from one individual to another. For most patients with HD, the initial symptoms include involuntary motor movements, interrupted pursuit of gaze, and uncontrolled reflexive glances to novel visual stimuli. Psychological symptoms, such as sadness and depression, can also occur during the early stages of the disease (4). Subsequently, there are other physiological and cognitive problems in early-middle, middle, and middle-late stages. Eventually, the patient will experience bowel and bladder control difficulties (1). Current research has suggested that the rate of HD progression is more rapid in juvenile-onset and more gradual in adult-onset. In one study conducted in Venezuela, juvenile-onset cases showed cognitive and motor deteriorations twice as fast as adult-onset cases (5). Even though symptoms vary, death occurs about 15 to 20 years after initial onset. Patients with HD do not recover from the illness as a result of treatment.

Prevalence

The prevalence of Huntington’s disease varies worldwide. There are no reported incidence rates for this disorder (6). The disorder is highly heritable. There is a 50% chance of inheriting the disease if an individual is born to a parent with HD. Approximately 6% of patients with HD have early onset before the age of 20, and 25% have onset after the age of 50  (1). Most people begin to experience symptoms during early to middle adulthood.

Neuropathology

In the brains of HD patients, there is severe neuronal loss in selective areas of the caudate nucleus and putamen. As a result of neuronal loss, several brain structures are affected, including the globus pallidus, thalamus, subthalamic nucleus, white matter, and cerebellum. The main affected area is the cerebellum, which leads to difficulties with balance and coordination. (1).

Treatments

There is no cure for HD. There are medications and therapies available to alleviate the symptoms. Speech and language therapy, occupational therapy, physical therapy, and nutritional support are methods that may help improve some of the symptoms experienced (1).

References

  1. Paulsen, J, & Mikos, A (2008). Huntington’s disease. In J Morgan & J Ricker (Eds.), Textbook of clinical neuropsychology (pp. 616-635). Philadelphia: Taylor & Francis.
  2. Paulsen, J, Ready, R, Hamilton, J, Mega, M, & Cummings, J (2001). Neuropsychiatric aspects of Huntington’s disease. Journal of Neurology, Neurosurgery & Psychiatry71(3), 310-314.
  3. Almqvist, E, Bloch, M, Brinkman, R, Craufurd, D, & Hayden, M (1999). A worldwide assessment of the frequency of suicide, suicide attempts, or psychiatric hospitalization after predictive testing for Huntington disease.The American Journal of Human Genetics64(5), 1293-1304.
  4. Kirkwood, S, Su, J, Conneally, P, & Foroud, T (2001). Progression of symptoms in the early and middle stages of Huntington disease. Archives of neurology58(2), 273-278.
  5. Young, A, Penney, J, Starosta‐Rubinstein, S, Markel, D, Berent, S, Giordani, B, & Hichwa, R (1986). PET scan investigations of Huntington’s disease: cerebral metabolic correlates of neurological features and functional decline. Annals of neurology20(3), 296-303.
  6. Rawlins, M, Wexler, N, Wexler, A, Tabrizi, S, Douglas, I, Evans, S, & Smeeth, L (2016). The Prevalence of Huntington’s disease. Neuroepidemiology,46(2), 144-153.