Huntington's disease

Medical quality assurance by Dr. Albrecht Nonnenmacher, MD at March 31, 2016
StartHuntington's disease

Huntington’s disease is an inherited progressive disorder that attacks the nerve cells of the brain. As the disease progresses, it severely impacts the person’s physical and cognitive abilities and can cause behavioral changes. Approximately 30,000 Americans live with the symptoms of Huntington’s, and another 200,000 are at risk of inheriting the condition.

Contents

Definition & Facts

Huntington’s disease is named after Dr. George Huntington, who was the first to describe the condition at the end of 19th century. Most people with Huntington’s first develop symptoms during their 30s or 40s, and the symptoms worsen over the next 10 to 25 years. In cases where the onset of symptoms occurs before age 20, the disease typically progresses faster, and the symptoms may present slightly differently.

Everyone has the Huntington’s gene; however, only individuals who carry a particular expansion of the gene will go on to develop the condition. Everyone with this genetic mutation will eventually develop Huntington’s disease. A child of a parent with Huntington’s disease has a 50/50 chance of carrying the expanded Huntington’s gene.

Symptoms & Complaints

Huntington’s has been described as being similar to Parkinson’s disease, Alzheimer’s disease, and Lou Gehrig’s disease. Symptoms can vary from person to person and may be exacerbated by excitement or stress. Huntington’s symptoms typically develop in stages:

  • Early stage symptoms may be subtle, and the individual may still be able to work or perform daily tasks with only minimal assistance. The person may notice that they are clumsier than normal and that their movements are slow and stiff. The individual may begin to fidget uncontrollably. They may also begin to have mood changes and have difficulty processing information and thinking through problems.
  • During the middle stages of the disease, the individual may fall or drop things frequently and may have difficulty swallowing and difficulty speaking. As a result, they may require more assistance with day-to-day activities. The cognitive symptoms make it difficult to stay organized and behavioral changes may strain relationships.
  • Individuals with late-stage Huntington’s are usually reliant on others for their care. Most will still be aware of those around them but will be unable to speak or walk. The jerky movements associated with the condition may become worse.

Causes

Researchers discovered the gene that causes Huntington’s in 1993. The gene is responsible for creating the blueprint for a protein called huntingtin protein. The genetic defect in the huntingtin gene causes extra repetitions for the code for this protein. The normal function of the protein has yet to be determined; however, the defective version of the protein causes the brain changes responsible for the symptoms of Huntington’s disease.

Huntington’s is an autosomal dominant disorder, which means that an individual only needs to inherit one copy of the defective gene to develop Huntington’s. Both sexes have an equal chance of inheriting the defective gene. People who do not have the defective version of the gene cannot develop Huntington’s or pass it along to their children. It is not possible for Huntington’s to skip generations.

Diagnosis & Tests

Diagnostic genetic tests are available for individuals with suspected Huntington’s disease to confirm the diagnosis. The tests measure the number of repeats of the huntingtin protein contained within the fourth chromosome. Normally, the chromosome will contain 17 to 20 repetitions of the code. Individuals with the defective version of the gene will typically have 40 or more repeated codes.

People with a family history of Huntington’s but who are still asymptomatic may choose to undergo predictive genetic testing. Predictive testing does not provide information on when symptoms may first develop or which symptoms will appear first. Genetic testing is also not helpful in developing a treatment plan or delaying the onset of the disease.

Predictive genetic testing should only be performed after the individual has consulted a genetic counselor in order to fully understand the risks and benefits of testing. Some individuals prefer knowing so that they can plan for the future and make informed decisions regarding having children.

At-risk individuals wishing to have a child that is free of the defective gene can use pre-genetic diagnostic testing in conjunction with in vitro fertilization to ensure that the implanted embryo does not have the abnormal Huntington’s gene. Fetal testing can also be performed through amniocentesis or chorionic villus sampling between the 10th and 18th weeks of pregnancy.

Treatment & Therapy

There is no cure for Huntington’s disease. Most individuals with the condition ultimately die from complications, such as pneumonia or choking. Treatment and therapy are aimed at lessening symptoms but do not alter the progression and course of the disease.

Drug therapy is likely to evolve as the disease progresses. Medications, such as tetrabenazine, haloperidol, chlorpromazine, and risperidone may help control the involuntary movements associated with Huntington’s.

Antidepressants, antipsychotics, and mood-stabilizing medications may be beneficial in treating the psychiatric symptoms of Huntington’s. It is possible for treatments aimed at controlling one symptom of the disease to worsen other symptoms, so it is important to regularly review the treatment plan with the healthcare team.

Prevention & Prophylaxis

The symptoms and progression of Huntington’s are inevitable. A multidisciplinary support team can help individuals cope with the effects of living with the disease. A mental health professional, such as a psychologist, psychiatrist, or social worker, is often an essential part of the treatment team for individuals facing Huntington’s. They can use talk therapy and recommend coping strategies to help the individual manage behavioral issues.

They can also facilitate communication between the patient and their family and help manage expectations as the disease progresses. Speech therapy and language therapy can be beneficial in addressing problems with speaking and swallowing.

Occupational therapy and physical therapy can help the patient learn strategies for controlling involuntary movements as well as suggest assistive devices to help maintain safety and independence. Nutritionists can recommend appropriate diets to combat the unintentional weight loss often associated with Huntington’s disease.