Conditions

Huntington's Disease


About Huntington's Disease

Huntington's disease is a inherited progressive brain disorder caused by a single defective gene on chromosome 4, one of the 23 human chromosomes that carry a person’s entire genetic code.

This defect is ``dominant`` meaning that anyone who inherits it from a parent with Huntington's will eventually develop the disease. The disorder is named after George Huntington, the physician who first described it in the late 1800s.

The defective gene codes the blueprint for a protein called huntingtin. This protein's normal function isn't yet known, but it's called ``huntingtin`` because scientists identified its defective form as the cause of Huntington's disease.

Defective huntingtin protein leads to brain changes that cause abnormal involuntary movements, a severe decline in thinking and reasoning skills, and irritability, depression and other mood changes.

Symptoms

Huntington's disease usually causes movement, cognitive and psychiatric disorders with a wide spectrum of signs and symptoms. Which symptoms appear first varies greatly among affected people. During the course of the disease, some disorders appear to be more dominant or have a greater effect on functional ability.

  • Movement disorders – The movement disorders associated with Huntington's disease can include both involuntary movement problems and impairments in voluntary movements, such as:
    • Involuntary jerking or writhing movements (chorea)
    • Muscle problems, such as rigidity or muscle contracture (dystonia)
    • Slow or abnormal eye movements
    • Impaired gait, posture and balance
    • Difficulty with the physical production of speech or swallowing
  • Cognitive disorders - Cognitive impairments often associated with Huntington's disease include:
    • Difficulty organizing, prioritizing or focusing on tasks
    • Lack of flexibility or the tendency to get stuck on a thought, behaviour or action (perseveration)
    • Lack of impulse control that can result in outbursts, acting without thinking and sexual promiscuity
    • Lack of awareness of one's own behaviours and abilities
    • Slowness in processing thoughts or ''finding'' words
    • Difficulty in learning new information
  • Psychiatric disorders - The most common psychiatric disorder associated with Huntington's disease is depression. Depression appears to occur because of injury to the brain and subsequent changes in brain function. Signs and symptoms may include:
    • Feelings of irritability, sadness or apathy
    • Social withdrawal
    • Insomnia
    • Fatigue and loss of energy
    • Frequent thoughts of death, dying or suicide
    Other common psychiatric disorders include:
    • Obsessive-compulsive disorder - a condition marked by recurrent, intrusive thoughts and repetitive behaviours
    • Mania - which can cause elevated mood, overactivity, impulsive behaviour and inflated self-esteem
    • Bipolar disorder - a condition with alternating episodes of depression and mania

Symptoms of juvenile Huntington's disease The start and progression of Huntington's disease in younger people may be slightly different from that in adults. Problems that often present themselves early in the course of the disease include:

  • Behavioural changes
  • Loss of previously learned academic or physical skills
  • Rapid, significant drop in overall school performance
  • Behavioural problems
  • Physical changes
  • Contracted and rigid muscles that affect gait (especially in young children)
  • Changes in fine motor skills that might be noticeable in skills such as handwriting
  • Tremors or slight involuntary movements
  • Seizures

Causes

Huntington's disease is caused by an inherited defect in a single gene. Huntington's disease is an autosomal dominant disorder, which means that a person needs only one copy of the defective gene to develop the disorder.

With the exception of genes on the sex chromosomes, a person inherits two copies of every gene - one copy from each parent. A parent with a defective gene could pass along the defective copy of the gene or the healthy copy. Each child in the family, therefore, has a 50 percent chance of inheriting the gene that causes the genetic disorder.

Diagnosis

Scientists identified the defective gene that causes Huntington's disease in 1993. A diagnostic genetic test is now available. The test can confirm that the defective gene for huntingtin protein is the cause of symptoms in people with suspected Huntington's disease and can detect the defective gene in people who don't yet have symptoms but are at risk because a parent has Huntington's.

Treatment

There is currently no cure for Huntington's disease and no way to slow or stop the brain changes it causes. Treatments focus on managing symptoms. A group of international experts recommended the following treatments as first-line strategies for three of the disease's most troubling symptoms:

  • Chorea (involuntary movements): Some experts believe beginning treatment with an atypical antipsychotic drug, such as olanzapine, is best. Others start with another type of drug recently approved by the U.S. Food and Drug Administration (FDA) specifically for Huntington’s, called tetrabenazine.
  • Irritability: For severe anger and threatening behaviour, experts agree that an atypical antipsychotic drug is the preferred approach. For less severe, nonthreatening irritability, experts recommend first trying a selective serotonin reuptake inhibitor (SSRI), which is a type of antidepressant.
  • Obsessive-compulsive thoughts and actions: Experts also recommend SSRIs as the standard treatment for these symptoms.
Other Huntington's symptoms, such as anxiety, depression and insomnia, also should be treated according to generally accepted guidelines and benefit greatly from frail care assistance. Experts encourage people with Huntington's to keep all their medical appointments and not to get discouraged if it takes their health care team some time to find the best drugs and the most effective doses.