Huntington’s disease is a disease that causes the breakdown and death of nerve cells in the brain. It’s progressive, which means it steadily worsens over time. Most people inherit the disorder from a parent, but in some cases, a person can have Huntington’s without a family history. GenomeSmart can help you understand the role of genetic testing as you plan your family.

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Huntington’s Disease – Can genetic
testing help?
8 min readReproductive Genetics
Huntington’s disease is a disease that causes the breakdown and death of nerve
cells in the brain. It’s progressive, which means it steadily worsens over time. Most
people inherit the disorder from a parent, but in some cases, a person can have
Huntington’s without a family history. It causes an individual to have jerky and
involuntary movements, known as chorea, which is why this disease is sometimes
referred to as Huntington’s chorea.
There is no discrimination in Huntington’s disease. It affects both men and
women in all races and ethnicities. According to the World Health Organization,
Huntington’s disease affects about five to seven out of 100,000 people in Western
countries. Symptoms typically start in a person’s 30s and 40s, and death usually
comes 15-20 years from the time the symptoms started.
How is Huntington’s disease inherited?
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Huntington’s disease is considered an autosomal dominant mutation. This means
a person only needs one copy of the mutation to have the disease. It occurs when
the Huntingtin gene, also known as the HTT gene, has a mutation. This gene itself
isn’t completely understood by researchers, and it’s so named because Dr.
George Huntington, who was one of the first to study the disease, named it after
himself.
The HTT gene is responsible for coding for the Huntingtin protein. When it
mutates, it changes the structure of the Huntingtin protein. This change in the
HTT gene alters how the protein works in the body, damaging brain cells by
clumping up and killing them. The brain cells most affected are those that are
responsible for voluntary movement, thought, and memory. If a parent has a
mutated HTT gene, each of their children will have a 50% chance of having the
disorder themselves.
What actually causes the mutation in the HTT gene is an expansion of the
cytosine-adenine-guanine, or CAG, repeat sequence. Chromosomes are made up
of long strands of human DNA. DNA is made up of bases: A, C, G, or T that pair up.
People who have Huntington’s have an abnormally long stretch of repeated
sequences of CAGs. People with Huntington’s have an average of 40-50 of these r
epeats. To put it in perspective, people who don’t have Huntington’s have about
17 of these repeat CAGs, and anything more than 36 is suspicious of
Huntington’s. Unfortunately, the size of the CAG repeats tend to increase in size
with every generation it is passed down to, and these long repeats are associated
with an earlier onset of symptoms than the generations before them.
Signs and symptoms
A person who has the gene mutation will start noticing signs that something is
wrong around 30-40 years old. They can be subtle, with slight changes in
someone’s mood or their ability to recall memories. They could start noticing
they’re slightly unsteady on their feet, or feel like they’re body isn’t quite balanced.
As the disease progresses, the involuntary movements worsen. Talking becomes
more difficult because it’s hard for a person to now form words with their mouth.

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Rigid muscles and contractures occur, which make walking and standing upright
harder. They could also have problems moving the muscles for their eyes.
Many people with the disease underestimate how bad their symptoms really are.
Much of this is due to the steady decline of cognitive function. Judgment and
emotional state can be impaired. Anxiety, irrational anger, and becoming easily
frustrated occur in many people. Depression is the most common psychiatric
problem and this is actually due to changes in the brain as a result of the disease,
rather than being upset with the diagnosis of Huntington’s disease.
Weight loss is a very common issue in people diagnosed with Huntington’s. Much
of this is due to the constant movements and the sheer amount of calories that
are burned because of always moving.
In the late stages of the disease, the damage to the nerve cells takes over almost
every aspect of a person’s body. They may have worsening chorea — jerky
movements — but in some cases these movements will stop. The person
becomes unable to leave their bed, and they can no longer talk. However, they
can remain aware of their surroundings. Dementia is a devastating result of long
term Huntington’s.
Diagnosis
Diagnosing Huntington’s disease involves getting a full medical and family history.
Doctors may do magnetic resonance imaging (MRI) to scan the brain looking for
areas of damage. This may not be an accurate form of diagnosis in the early
stages of the disease, but it can help rule out other causes of a person’s
symptoms. Other tests include a physical and neurological exam. Neurological
testing looks for memory or language concerns, and a possible psychiatric
evaluation looks for signs of anxiety, depression, or other mood disorders.
If a person isn’t having any symptoms, a diagnosis of Huntington’s disease can be
discovered by genetic testing, to find out if a person has the HTT gene mutation.
As stated above, there may be a family history of Huntington’s, but there might
not be. A lot of consideration needs to go into testing for Huntington’s. Since

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there is no way of preventing or stopping the disease, there is an ethical dilemma
on whether or not to get the test. Some people may not want to know that they
are going to get the disease at some point in their life. They can’t do anything
about it, so they don’t want to spend their time focusing on it. But for some, if
there is a family history, they want to know so that they can plan for the future,
and the future of their family.
Once a person knows they have the disease, there are several options to consider
if they want to have children. They could choose to do in vitro fertilization, or IVF.
In this process, eggs are taken from a woman’s ovaries and fertilized with her
partner’s sperm in a laboratory setting. The resulting embryos that develops can
then be tested, a process called preimplantation genetic diagnosis. This will tell
which embryos have the disease or not. The embryos that don’t contain the HTT
gene mutation can then be transferred back unto the woman’s uterus, ensuring
she will not have a baby with Huntington’s. If the mother or father doesn’t want to
use their own eggs or sperm, they can go through an egg or sperm donor instead,
bypassing their genetics altogether.
Another family-building option is to test the fetus once a woman is pregnant to
find out if it has the mutation. This is done by taking a sample from the fetus and
testing its DNA, through chorionic villus sampling (CVS) or amniocentesis. From
there, if the results show the baby has the gene mutation for Huntington’s
disease, the parents can decide if they want to continue with the pregnancy or
plan for the future.
Treatments
Tetrabenazine is a relatively new medication approved by the FDA to treat the
symptoms of uncontrolled muscle movements. Antipsychotic medications can be
given to help with the more difficult emotions, such as hallucinations and
outbursts of anger. For depression and anxiety, doctors can prescribe
medications to help ease symptoms. However, many of these medications cause
side effects such as extreme tiredness, sedation and troubles focusing, so doctors
and patients need to weigh the risks versus the benefits. Anxiety can be

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debilitating, and it can help to have support persons to provide encouragement,
especially because antianxiety and antidepressant medications can take a few
weeks to feel the effects.
Since the jerky movements caused by muscle nerve damage can impinge on a
person’s daily life, physical and occupational therapist are frequently involved to
help a person learn to control their movements as much as possible and to assist
with coping with their new lifestyle—finding new ways to perform the things they
used to do without thinking. Speech Language Pathologists can help teach a
person how to swallow without choking and learn to continue to speak after the
muscles in their face and jaw have been affected.
Since the jerky movements caused by muscle nerve damage can impinge on a
person’s daily life, physical and occupational therapist are frequently involved to
help a person learn to control their movements as much as possible and to assist
with coping with their new lifestyle—finding new ways to perform the things they
used to do without thinking. Speech Language Pathologists can help teach a
person how to swallow without choking and learn to continue to speak after the
muscles in their face and jaw have been affected.
Complications
Usually, it’s not the disease itself that kills people, it’s the complications that arise
from it. There is an increased risk of suicide which is why it’s so important to
regularly get evaluated and treated for the emotional symptoms that Huntington’s
disease may cause.
Complications can come about as a result of a person falling due to the
uncoordinated movements. They can become injured due to falls, which can lead
to more time being bedridden. In end-stage Huntington’s, the disease causes
people to need around-the-clock care.
As losing weight is an issue for people with Huntington’s disease, food may have
to be pureed, or fed from a feeding tube in later stages of the disease as the risk
of choking is very high. Swallowing becomes near impossible, and aspiration

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pneumonia (the inhaling of food or liquids into the lungs causing infection) is a
main cause of death.
GenomeSmart can help you understand the role of genetic testing as you plan
your family.
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