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.
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
Lack of impulse control that can result in outbursts, acting without
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:
Other common psychiatric disorders include:
Feelings of irritability, sadness or apathy
Fatigue and loss of energy
Frequent thoughts of death, dying or suicide
Obsessive-compulsive disorder - a condition marked by recurrent,
and repetitive behaviours
Mania - which can cause elevated mood, overactivity, impulsive behaviour
Bipolar disorder - a condition with alternating episodes of depression
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:
Loss of previously learned academic or physical skills
Rapid, significant drop in overall school performance
Contracted and rigid muscles that affect gait (especially in young children)
Changes in fine motor skills that might be noticeable in skills such as
Tremors or slight involuntary movements
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
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.
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.