Huntington's disease is a genetic, progressive, neurodegenerative disorder characterized by the gradual development of involuntary muscle movements affecting the hands, feet, face, and trunk and progressive deterioration of cognitive processes and memory (dementia). Neurologic movement abnormalities may include uncontrolled, irregular, rapid, jerky movements (chorea) and athetosis, a condition characterized by relatively slow, writhing involuntary movements. Dementia is typically associated with progressive disorientation and confusion, personality disintegration, impairment of memory control, restlessness, agitation, and other symptoms and findings. In individuals with the disorder, disease duration may range from approximately 10 years up to 25 years or more. Life-threatening complications may result from pneumonia or other infections, injuries related to falls, or other associated developments.

Huntington's disease is transmitted as an autosomal dominant trait. The disease results from changes (mutations) of a gene known as "huntington" located on the short arm (p) of chromosome 4 (4p16.3). In those with the disorder, the huntington gene contains errors in the coded "building blocks" (nucleotide bases) that make up the gene's instructions. The gene contains abnormally long repeats of coded instructions consisting of the basic chemicals cytosine, adenine, and guanine (CAG trinucleotide repeat expansion). The length of the expanded repeats may affect the age at symptom onset. The specific symptoms and physical features associated with Huntington's disease result from degeneration of nerve cells (neurons) within certain areas of the brain (e.g., basal ganglia, cerebral cortex).

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 unusual eye movements
• Impaired gait, posture and balance
• Difficulty with speech or swallowing

Impairments in voluntary movements — rather than involuntary movements — may have a greater impact on a person's ability to work, perform daily activities, communicate and remain independent.

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, behavior 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 behaviors 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. This isn't simply a reaction to receiving a diagnosis of Huntington's disease. Instead, 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 behaviors
• Mania, which can cause elevated mood, overactivity, impulsive behavior and inflated self-esteem
• Bipolar disorder, a condition with alternating episodes of Depression and mania

In addition to the above disorders, Weight loss is common in people with Huntington's disease, especially as the disease progresses.

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 early in the course of the disease include:

Behavioral changes

• Difficulty paying attention
• Rapid, significant drop in overall school performance
• Behavioral problems

Physical changes

• Contracted and rigid muscles that affect gait (especially in young children)
• Tremors or slight involuntary movements
• Frequent falls or clumsiness
• Seizures

Autosomal dominant inheritance pattern 

In an autosomal dominant disorder, the altered gene is a dominant gene located on one of the nonsex chromosomes (autosomes). You need only one altered gene to be affected by this type of disorder. A person with an autosomal dominant disorder — in this case, the father — has a 50% chance of having an affected child with one altered gene (dominant gene) and a 50% chance of having an unaffected child with two typical genes (recessive genes).

Huntington's disease is caused by an inherited difference in a single gene. Huntington's disease is an autosomal dominant disorder, which means that a person needs only one copy of the nontypical 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 nontypical gene could pass along the nontypical copy of the gene or the healthy copy. Each child in the family, therefore, has a 50% chance of inheriting the gene that causes the genetic disorder.

No treatments can alter the course of Huntington's disease. But medications can lessen some symptoms of movement and psychiatric disorders. And multiple interventions can help a person adapt to changes in abilities for a certain amount of time.

Medications will likely evolve over the course of the disease, depending on overall treatment goals. Also, drugs that treat some symptoms may result in side effects that worsen other symptoms. Treatment goals will be regularly reviewed and updated.

Psychotherapy

A psychotherapist — a psychiatrist, psychologist or clinical social worker — can provide talk therapy to help with behavioral problems, develop coping strategies, manage expectations during progression of the disease and help family members communicate with each other.

Speech therapy

Huntington's disease can significantly impair control of muscles of the mouth and throat that are essential for speech, eating and swallowing. A speech therapist can help improve your ability to speak clearly or teach you to use communication devices — such as a board covered with pictures of everyday items and activities. Speech therapists can also address difficulties with muscles used in eating and swallowing.

Physical therapy

A physical therapist can teach you appropriate and safe exercises that enhance strength, flexibility, balance and coordination. These exercises can help maintain mobility as long as possible and may reduce the risk of falls.

Instruction on appropriate posture and the use of supports to improve posture may help lessen the severity of some movement problems.

When the use of a walker or wheelchair is required, the physical therapist can provide instruction on appropriate use of the device and posture. Also, exercise regimens can be adapted to suit the new level of mobility.

Occupational therapy

An occupational therapist can assist the person with Huntington's disease, family members and caregivers on the use of assistive devices that improve functional abilities. These strategies may include:

• Handrails at home
• Assistive devices for activities such as bathing and dressing
• Eating and drinking utensils adapted for people with limited fine motor skills

People with a known family history of Huntington's disease are understandably concerned about whether they may pass the Huntington gene on to their children. These people may consider genetic testing and family planning options.

If an at-risk parent is considering genetic testing, it can be helpful to meet with a genetic counselor. A genetic counselor will discuss the potential risks of a positive test result, which would indicate that the parent will develop the disease. Also, couples will need to make additional choices about whether to have children or to consider alternatives, such as prenatal testing for the gene or in vitro fertilization with donor sperm or eggs.

Another option for couples is in vitro fertilization and preimplantation genetic diagnosis. In this process, eggs are removed from the ovaries and fertilized with the father's sperm in a laboratory. The embryos are tested for presence of the Huntington gene, and only those testing negative for the Huntington gene are implanted in the mother's uterus.

Medications for movement disorders

Drugs to treat movement disorders include the following:

• Drugs to control movement include tetrabenazine (Xenazine) and deutetrabenazine (Austedo), which have been specifically approved by the Food and Drug Administration to suppress the involuntary jerking and writhing movements (chorea) associated with Huntington's disease. These drugs don't have any effect on the progression of the disease, however. Possible side effects include drowsiness, restlessness, and the risk of worsening or triggering depression or other psychiatric conditions.

• Antipsychotic drugs, such as haloperidol and fluphenazine, have a side effect of suppressing movements. Therefore, they may be beneficial in treating chorea. However, these drugs may worsen involuntary contractions (dystonia), restlessness and drowsiness.

  Other drugs, such as olanzapine (Zyprexa) and aripiprazole (Abilify), may have fewer side effects but still should be used with caution, as they may also worsen symptoms.

• Other medications that may help suppress chorea include amantadine (Gocovri, Osmolex ER), levetiracetam (Keppra, Elepsia XR, Spritam) and clonazepam (Klonopin). However, side effects may limit their use.

Medications for psychiatric disorders

Medications to treat psychiatric disorders will vary depending on the disorders and symptoms. Possible treatments include the following:

• Antidepressants include such drugs as citalopram (Celexa), escitalopram (Lexapro), fluoxetine (Prozac) and sertraline (Zoloft). These drugs may also have some effect on treating obsessive-compulsive disorder. Side effects may include nausea, diarrhea, drowsiness and low blood pressure.
• Antipsychotic drugs such as quetiapine (Seroquel) and olanzapine (Zyprexa) may suppress violent outbursts, agitation, and other symptoms of mood disorders or psychosis. However, these drugs may cause different movement disorders themselves.
• Mood-stabilizing drugs that can help prevent the highs and lows associated with bipolar disorder include anticonvulsants, such as divalproex (Depakote), carbamazepine (Tegretol, Carbatrol, Epitol, others) and lamotrigine (Lamictal).