NAVIGATING HUNTINGTON′S DISEASE: LATEST RESEARCH, SUPPORT, TREATMENTS, AND MORE

Medically Reviewed by Dr. Sony Sherpa (MBBS) - August 26, 2024

Huntington’s disease is a rare dominant autosomal genetic disorder that leads to deterioration of the brain, causing progressive loss of physical and mental abilities. It is also known as Huntington’s chorea because one of the most common symptoms is involuntary movements of the limbs, face, and trunk.

In this article, we will explain what Huntington’s disease is, how it is diagnosed, what the symptoms and stages are, and cover current treatment options and the latest research.

What is Huntington’s Disease?

A mutation in the HTT, also known as the huntingtin gene, located on chromosome 4, results in Huntington's disease. This gene normally produces a protein called huntingtin, which is involved in many functions of the brain cells. HTT mutation causes the gene to produce a malformed version of huntingtin that has a long stretch of repeated CAG trinucleotides.^[1]

The longer the CAG repeat lengths in the HTT gene, the more likely the person will develop Huntington’s disease and the earlier the symptoms will appear. When present in children, the condition is referred to as juvenile Huntington’s disease^[2].

The abnormal huntingtin protein accumulates in brain cells and interferes with their normal functioning. Over time, this leads to the death of brain cells. This is especially common in the striatum, a brain area that governs decision-making, movement initiation, and control, as well as aspects of emotion, memory, and learning. The loss of brain cells causes the symptoms of Huntington’s disease to worsen over time.

How Common is Huntington's Disease?

Huntington’s Disease is not common, with the global prevalence averaging 2.7 instances per 100,000 people. Juvenile Huntington’s disease accounts for 5-10% of all cases. The prevalence may be higher due to limited testing and awareness of the condition. Testing usually only occurs within families in which Huntington’s Disease is already present.

Is Huntington's Disease Fatal?

The life expectancy of those with Huntington’s Disease is usually 15-20 years after diagnosis. Life expectancy can be almost accurately predicted through genetic testing. It is difficult to ascertain a precise Huntington’s disease prognosis as symptom severity and progression are not predictable.

Symptoms of Huntington’s Disease

The symptoms of Huntington’s disease vary from person to person and depend on the stage of the disease. The symptoms usually begin between the ages of 30 and 50 and are classified into three main categories: motor, cognitive, and psychiatric.

Motor Symptoms

The predominant sign of the disorder is Huntington's chorea, which is characterized by uncontrollable, abrupt, spastic, or jerky movements of the arms, legs, and face muscles.

Other motor symptoms include:

• Difficulty initiating or controlling voluntary movements
• Slurred speech and difficulty swallowing
• Muscle rigidity and spasms
• Balance problems and falls
• Gait abnormalities
• Weight loss and malnutrition
• Slower eye movement and related difficulties

Juvenile Huntington's disease symptoms are similar to adult presentations. Children with Huntington’s Disease are at a higher risk of developing seizures.

Cognitive Symptoms

The most common cognitive symptoms of Huntington's Disease include:

• Memory loss and difficulty learning new information
• Impaired judgment and decision-making
• Difficulty planning and organizing
• Reduced attention and concentration
• Difficulty finding words and communicating

End-stage Huntington’s disease can give rise to dementia.

Behavioral and Psychiatric Symptoms

Psychiatric and behavioral symptoms may be present early during the disease before motor symptoms become apparent.

Common psychiatric symptoms include:

• Depression and anxiety
• Irritability and aggression
• Mood swings and emotional instability
• Apathy and social withdrawal
• Psychosis and hallucinations, in some cases

It is important for caregivers to be aware of depression, possible suicidal ideation, and the risk of suicide among patients.

The 5 Stages of Huntington's Disease

The progression of Huntington’s disease can be divided into five stages: early, early intermediate, late intermediate, early advanced, and advanced. ^[3]

Each stage is characterized by different levels of functional impairment and dependence on caregivers.

0. Preclinical stage: Symptoms are not present during this stage, and individuals do not fulfill the diagnostic criteria. Genetic tests or imaging may still be able to confirm the disease.
1. Early stage: This is the stage when symptoms first start to occur, yet it is still too early to detect the disease as symptoms are mild. The person may have mood problems, difficulty learning new things, or poor coordination.
2. Early Intermediate stage: This is the stage when the diagnosis of HD is often made, based on the presence of involuntary movements called chorea. The person may have trouble with eating, sleeping, thinking, or communicating. They may still be able to work or drive with difficulty and may require assistance.
3. Late Intermediate stage: In this stage, the motor symptoms intensify, and the person needs substantial assistance in daily activities. Cognitive decline and difficulties swallowing, speaking, walking, or balancing are common.
4. Early Advanced stage: Motor disturbances are at their worst in this stage. The person may have slow and rigid movements, speech impairment, and dementia.
5. Advanced stage: This is the final stage of Huntington’s Disease. Chorea may lessen and be replaced by slowness, stiffness, and other symptoms that resemble Parkinson’s disease. Mortality during end-stage Huntington’s disease is usually due to complications.

The duration of each stage varies from person to person, but on average, the disease lasts for about 15 to 20 years after diagnosis.

Huntington's Disease vs Parkinson's Disease

Huntington’s disease and Parkinson’s disease are both neurodegenerative diseases that affect the brain and cause problems with movement, cognition, and emotion. Yet, they have different causes and symptoms. Huntington’s disease is genetically inherited and characterized mainly by chorea or involuntary jerky movements. Parkinson’s disease is caused by the loss of dopamine-producing neurons in the brain that results in tremors and loss of movement control.

How is Huntington’s Disease Diagnosed?

Huntington’s disease is diagnosed by a combination of genetic testing, neurological examination, and brain imaging:

Genetic Testing: To test for Huntington’s disease, genetic profiling can confirm the presence of the HTT mutation and determine the number and length of CAG repeats. This can help predict the likelihood and age of onset of the disease. The severity and rate of progression of Huntington's disease symptoms cannot be predicted by genetic testing. It is usually done only for people who have a family history of Huntington’s disease or who have symptoms suggestive of the disease.

Neurological Examination: Involuntary movements, poor coordination, cognitive deterioration, and mood swings can all be identified during a neurologist's examination of a patient's physical and mental abilities.

Brain Imaging: A CT scan or MRI can show the extent of brain atrophy (shrinkage) and identify any other possible causes of the symptoms.

Current Huntington’s Disease Treatments

Sadly, there is currently no cure for Huntington's disease. Current treatments are aimed at managing some of the symptoms and improving the quality of life for the affected person and their caregivers.

Medications

Huntington’s Disease medication targets specific symptoms and often includes antidepressants and antipsychotics. Tetrabenazine and deutetrabenazine are vesicular monoamine transporter 2 (VMAT2) inhibitors, commonly used to treat chorea. These medications work by depleting dopamine in the brain, reducing involuntary, jerky movements. Deutetrabenazine is a modified version with a longer duration of action and potentially fewer side effects compared to tetrabenazine^[4]. Side effects can include sedation, weight gain, nausea, or worsening of cognitive function.

It is important to consult with a qualified neurologist about the best prescriptions for the patient’s unique needs and to go for checkups when symptoms intensify or new symptoms develop.

Huntington’s Disease Therapies

Available therapies for Huntington’s Disease include:

• Physical therapy is beneficial for maintaining muscle strength, flexibility, balance, and mobility. It can help prevent falls, injuries, contractures, and pressure sores.
• Occupational therapy improves the patient’s ability to carry out daily activities such as dressing, eating, bathing, using the toilet, etc. A qualified occupational therapist can also provide adaptive devices and strategies to enhance safety, comfort, and independence.
• Speech therapy helps with communication and swallowing problems. It can teach the patient alternative methods of communication, such as sign language, gestures, or using devices.
• Psychotherapy from a psychologist, psychiatrist, counselor, or social worker can help those with the condition and their families to better cope with the emotional and psychological impact of the disease. A therapist may also provide guidance and resources for dealing with relevant challenges and issues.

Palliative care

Palliative care is useful during end-stage Huntington’s disease, providing severe symptom management, pain relief, and end-of-life care. It also addresses the spiritual, social, and ethical issues related to the disease.

Recent Advances in Huntington’s Disease Research

In addition to these treatments, there are ongoing research efforts to find a cure or a way to slow down or stop the progression of Huntington’s disease. Some promising areas of research include^[5]:

• Gene Therapy: Gene therapy aims to deliver a normal copy of the HTT gene or a gene that can block or reduce the production of the abnormal huntingtin protein. This can potentially prevent or reverse the damage to the brain cells.
• Antisense Oligonucleotides (ASOs): ASOs are short pieces of DNA or RNA that can bind to and silence the HTT gene or the messenger RNA that carries its instructions. This can reduce the amount of abnormal huntingtin protein in the brain cells.
• Small Molecules: Small molecules are compounds that can modulate the activity or function of the abnormal huntingtin protein or its interacting partners. This can prevent or correct the harmful effects of the protein on the brain cells.
• Stem Cell Therapy: Stem cell therapy aims to replace the lost or damaged brain cells with healthy ones derived from stem cells. These stem cells can be obtained from the person’s own body or from donors.

These and many more future treatment approaches are still in the experimental stages and require further testing and validation before they can be used in humans. However, they offer hope and optimism for the future of Huntington’s disease treatment.

Support for Patients and Families

Huntington’s disease is not only a challenge for the person who has it but also for their family, friends, and caregivers. Living with Huntington’s disease can be stressful, isolating, and overwhelming. It is important to seek and receive support.

Aside from psychotherapy, support can be found through the following avenues:

• Joining a support group for Huntington’s Disease can provide emotional, practical, and informational support, as well as a sense of belonging and community. You can find local or online support groups through organizations such as the UK’s Huntington’s Disease Association or Huntington’s Disease Society of America.
• Accessing educational materials and resources helps you to better understand what to expect, how to plan ahead, and how to make informed decisions. You can find reliable and up-to-date information from websites such as HDBuzz or Huntington’s Outreach Project for Education at Stanford.
• Participating in research studies or clinical trials can offer hope and optimism for the future of Huntington’s disease treatment, as well as provide access to new or experimental therapies. You can find out more about ongoing research studies and clinical trials from websites such as ClinicalTrials.gov or HD Trial Finder.

Conclusion

Huntington’s disease is a rare genetic disorder that affects the brain and causes progressive loss of physical and mental abilities. It is caused by a mutation in the HTT gene that produces an abnormal huntingtin protein, which leads to brain degeneration. The symptoms of Huntington’s disease include involuntary movements, cognitive decline, and psychiatric problems. The disease progresses through five stages, with a common life expectancy of 15 to 20 years after diagnosis. Huntington's disease has no known cure, although there are treatments that can manage some of the symptoms and enhance the quality of life. Research efforts are currently underway to find better treatment options.

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