Huntington’s disease is an incurable, hereditary brain disorder that damages brain cells. It has a wide-ranging impact, affecting movement, thinking, and mood.
Huntington’s disease happens when a faulty gene causes toxic proteins to collect in the brain.
Huntington’s disease affects 3–7 individuals in every 100,000 people of European ancestry. It appears to be less common in people of Japanese, Chinese, and African descent, according to Genetics Home Reference.
The first signs normally appear between the ages of 30 and 50 years.
Huntington’s disease is a neurological condition. It is an inherited disease that results from faulty genes. Toxic proteins collect in the brain and cause damage, leading to neurological symptoms.
As the disease affects different parts of the brain, it impacts movement, behavior, and cognition. It becomes harder to walk, think, reason, swallow, and talk. Eventually, the person will need full-time care. The complications are usually fatal.
There is currently no cure, but treatment can help with symptoms.
Signs and symptoms are most likely to appear between the ages of 30 and 50 years, but they can occur at any age. Eventually, the disease or its complications can be fatal.
The key symptoms include:
- personality and mood changes
- problems with memory, thinking, and judgment
- loss of coordination and control of movements
- difficulty swallowing and speaking
The development of symptoms can vary between individuals. Some people will experience depression first and then changes in motor skills. Mood changes and unusual behavior are common early signs.
Early signs and symptoms
A doctor may not recognize the early symptoms if there has been no previous diagnosis of Huntington’s disease in the family. It can take time to reach a diagnosis.
Initial signs and symptoms include:
- slight uncontrollable movements
- small changes in coordination and clumsiness
- slight signs of mood and emotional change
- difficulty focusing and functioning at school or work
- lapses in short-term memory
The person may lose motivation and focus. They may appear lethargic and lacking in initiative.
Other possible signs of Huntington’s disease may include stumbling, dropping things, and forgetting people’s names. However, most people do these from time to time.
The middle and later stages
In time, symptoms become more severe.
These include physical changes, loss of motion control, and emotional and cognitive changes.
The person may experience:
- difficulty speaking, including looking for words and slurring
- weight loss, leading to weakness
- difficulty eating and swallowing, as the muscles in the mouth and diaphragm may not work properly
- risk of choking, especially in the later stages
- uncontrollable movements
There may be uncontrollable body movements, including:
- uncontrollable movements of the face
- jerking of parts of the face and the head
- flicking or fidgety movements of the arms, legs, and body
- lurching and stumbling
As Huntington’s disease progresses, the uncontrollable movements occur more often and usually with more intensity. Eventually they may become slower as the muscles become more rigid.
These may alternate rather than occurring consistently.
- antisocial behavior
- lack of emotion becomes more apparent
- cognitive changes
There may be:
- a loss of initiative
- a loss of organizational skills
- difficulty focusing
- problems with multitasking
The later stage
Eventually, the person will no longer be able to walk or talk, and they will need full nursing care.
However, they will usually understand most of what they hear and will be aware of friends and family members.
The inability to do things that used to be easy can lead to frustration and depression.
Weight loss can make the symptoms worse and weaken the patient’s immune system, making them more vulnerable to infections and other complications.
Huntington’s disease itself is not usually fatal, but choking, pneumonia, or another infection can be.
Huntington’s disease results from a faulty gene (mhTT) on chromosome number 4.
A normal copy of the gene produces huntingtin, a protein. The faulty gene is larger than it should be. This leads to excessive production of cytosine, adenine, and guanine (CAG), the building blocks of DNA. Normally, CAG repeats between 10 and 35 times, but in Huntington’s disease, it repeats from 36 to 120 times. If it repeats 40 times or more, symptoms are likely.
This change results in a larger form of the huntingtin protein, which is toxic. As it accumulates in the brain, it damages certain brain cells.
Some brain cells are sensitive to the larger form of huntingtin, especially those related to movement, thinking, and memory.
It undermines their function and eventually destroys them. Scientists are not sure exactly how this happens.
How is it passed on?
Huntington’s disease is an autosomal dominant disorder. This means a person can have it if they inherit only one copy of the faulty gene, from either their mother or their father.
A person with the gene has one good copy of the gene and one faulty copy. Any offspring will inherit either the good copy or the faulty one. The child who inherits the good copy will not develop Huntington’s disease. The child who inherits a faulty copy will.
Each child has a 50% chance of inheriting the faulty gene. If they inherit the faulty gene, each of their children will have a 50% chance of inheriting it. It can affect several generations.
A person who does not inherit the faulty gene will not develop the disease and cannot pass it on to their children. A child who inherits the faulty gene will develop Huntington’s if they reach the age when symptoms are due to emerge. Around 10% of people with the faulty gene develop symptoms before the age of 20, and around 10% develop them after the age of 60 years.
If symptoms start before the age of 20 years, this is juvenile Huntington’s disease.
The symptoms are different, and can include leg stiffness, tremors, and regression in learning.
Huntington’s disease is currently incurable. Treatment cannot reverse its progression or slow it down.
However, medication and other therapies can help manage some symptoms.
Tetrabenazine (Xenazine) has approval from the Food and Drug Administration (FDA) to treat the jerky, involuntary movements, or chorea, that can occur with Huntington’s disease.
Side effects include depression and suicidal thoughts or actions. If a person has signs of depression or mood changes when taking this drug, they should contact their doctor at once.
Tretrabenazine is not suitable for anyone who already has a diagnosis of depression, especially with suicidal thoughts.
Drugs to control movements, outbursts, and hallucinations may include:
- clonazepam (Klonopin)
- clozapine (Clorazil)
Adverse effects include sedation, stiffness, and rigidity.
For depression and some obsessive-compulsive features, a doctor may prescribe:
Lithium may help with extreme emotions and mood changes.
Speech therapy can help people find ways to express words and phrases and communicate more effectively.
Physical and occupational therapy
A physical therapist can help improve muscle strength and flexibility, improving balance and reducing the risk of falling.
An occupational therapist can help develop strategies for managing concentration and memory problems. They can also advise on making the home safer.
The doctor will examine the person and ask about family and medical history, and symptoms, such as recent emotional changes.
If they believe a person may have Huntington’s, they will refer them to a neurologist.
Doctors sometimes recommend imaging tests, such as a CT or MRI scan. These can identify changes in brain structure and help rule out other disorders.
Genetic testing may also help confirm a diagnosis.
Huntington’s disease has a significant emotional, mental, social, and economic impact on the life of an individual and their loved ones. Most people with this condition will live for 10–30 years after a diagnosis.
Juvenile onset Huntington’s disease usually progresses more rapidly. It may be fatal within 10 years of a diagnosis.
The cause of death is often a complication, such as pneumonia or choking.
There is currently no cure, but treatment can help people manage the condition and improve their quality of life.
Hope for the future?
In the future, scientists hope that gene therapy will find a solution to this disease. Researchers have been looking for ways to use gene therapy for cure, slow, or prevent Huntington’s disease.
One possible strategy is to use molecules known as synthetic small interfering RNAs (siRNAs) to suppress protein production from the faulty gene. This would stop the toxic Huntingtin protein from collecting and causing symptoms.
However, the challenge is how to deliver the siRNAs to the appropriate brain cells, so that they can be effective.
In 2017, scientists from Emory University suggested that CRISPR/Cas9 techniques, which involve “cutting and pasting” DNA, could help prevent Huntington’s disease in the future.
Experiments in mice have shown “significant improvements” after 3 weeks. Most of the traces of the damaging protein had gone, and the nerve cells showed signs of healing themselves.
Much more research is needed before humans can try this, however.
Organizations such as HDSA offer support for people with Huntington’s disease and their families.
Genetic testing for Huntington’s disease became possible in 1993. Anyone with a family history of the disease can ask their doctor about genetic testing to find out whether or not they carry the defective gene.
Some people prefer to find out if they have the gene, and if they are likely to develop symptoms, while other would rather not know. A genetic counselor can help with making the decision.
Huntington’s, genetics, and pregnancy
If a couple wish to have a child, and one parent has the faulty gene, it is possible to have in-vitro fertilization (IVF) treatment.
The embryo is then genetically tested in a laboratory and is only implanted into the woman if it does not have the faulty gene.
A fetus can also undergo genetic testing during gestation, if there is a family history of the disease. This can be done using chorionic villus sample (CVS) at 10–11 weeks, or through an amniocentesis at 14–18 weeks.