Huntington’s Disease Genetic Disorder & Diagnosis
Updated on April 2nd, 2019
Huntington’s is a rare but fatal disease that affects approximately 30,000 Americans per year. The symptoms come on slowly, before progressing to the point where a person’s quality of life suffers.
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Huntington’s is a rare disease that progresses over several years, affecting patients both mentally and physically. Eventually, the disease affects the person’s quality of life so seriously that it renders them virtually unable to care for themselves.
This disease has no cure and it’s a condition that ultimately results in death. The main cause behind the disease lies on chromosome 4 1 within the huntingtin protein gene and protein it creates.
Researchers identified the gene and protein in 1973, which has led to great strides in early detection and diagnosis, as well as treating the symptoms. However, while it’s possible to treat the symptoms, there is no way of stopping or slowing the progression at this time.
What Is Huntington’s Disease?
Huntington’s disease was first named in 1872 after George Huntington who was the first to describe the medical condition 2. The disease slowly destroys the brain’s cells due to an elongated huntingtin protein created by the huntingtin gene.
This condition isn’t caused by a defect or a mutation like you’ll find in many other diseases, but rather by a series of replications that result in a protein strand that’s too long for the body to handle.
Huntington’s is classified as a neurodegenerative disease, which means it attacks nerve cells. It’s mostly hereditary by nature, though there are times it has occurred spontaneously where there’s no family history of the disease.
This is a slow-progressing condition, with the exception of those who experience juvenile Huntington’s disease. In this case, instead of the typical 10 to 25 years of life after diagnosis, patients will experience quicker progression and pass away within 10 years.
Juvenile, which is the early-onset form of HD occurs when the disease affects those under 21 years of age 3. Normal Huntington’s appears during the 30 to 50 age range.
Is Huntington’s Disease Hereditary?
Yes, Huntington’s disease is a largely hereditary condition, though not everyone who has the disease will have parents or grandparents with the condition.
Likewise, just because parents pass on the gene repetition to their children doesn’t mean that the child will end up with the disease.
In many cases, a longer huntingtin protein doesn’t hinder a person because the body is equipped to handle them. It’s when the body fails to adapt to the longer protein strands that the disease takes root.
What Causes Huntington’s Disease?
Huntington’s disease is caused by excess production of the huntingtin protein. When the protein is too long, it tangles up with other proteins in a cell and causes them all to stop functioning.
As a result, the cells die off, resulting in the progressive nature of Huntington’s.
The huntingtin gene, known as the HTT gene, is located on chromosome 4. It has a DNA segment that’s known as a CAG trinucleotide repeat. In healthy people, this segment repeats between 10 and 35 times.
In the case of people with Huntington’s, the segment expansion ranges from 36 to over 120 repetitions 4.
Diagnosis of Huntington’s Disease
Only a doctor can diagnose Huntington’s disease, so even if you suspect you may have it because there’s a family history, a doctor’s diagnosis is critical to rule out any other possibilities.
How Do You Diagnose Huntington’s Disease?
In order to accurately diagnose the disease, doctors start out with a simple questionnaire and physical that examines your symptoms in-depth. Your family history is a vital piece of information, but even in the absence of this knowledge, doctors can still make a determination with more tests.
How Do Doctors Test for Huntington’s Disease?
Simple tests give doctors a lot of insight. Particularly, they will look for specific symptoms that indicate the onset of Huntington’s. These include changes in your motor skills, balance, and reflexes involving your muscles and coordination.
They’ll also examine you to detect any sensory problems and to determine if there are any changes in your mental or psychiatric health.
Abnormal movements and behaviors are one of the telltale signs of Huntington’s, so be completely upfront and honest with your doctor about any noticeable changes.
Huntington’s Disease and Genetics
Genetics are very much a large part of determining whether a person inherits or develops Huntington’s disease.
Because of the unnatural replication in the huntingtin gene, it affects the surrounding proteins in a cell, which can lead to the death of the cell 5 as a whole when it has no functioning parts left. Patients diagnosed with Huntington’s often do go through genetic testing at some point before the diagnosis is made.
Genetic Tests for Huntington’s Disease: Are They Available?
Genetic testing for Huntington’s is certainly available. Some at-home kits may offer the information, but the most reliable form is going to come from your physician’s office.
At-home kits look for markers for a wide range of diseases, while your physician can order one specifically looking at the HD gene.
DNA Testing to Spot or Detect Huntington’s Disease Early
If you have a family history of the disease, it’s only natural that you might want to assess your current risk. DNA tests to detect the abnormal HD gene on chromosome 4 can help to prepare you for the future.
The important thing, however, is to note that just because a person has the abnormality doesn’t mean that the disease is a certainty. Detecting it early can, however, ensure you know what to look for in regards to changes in your body.
DNA Tests Currently Available for Huntington’s Disease Include:
Currently, the most reliable DNA tests for Huntington’s come from a physician’s office.
Your doctor will order a genetic test based on a blood sample that they collect either in the office or at a designated lab.
Where Can I Go For a Genetic Test For my Child?
Getting your child tested is certainly a possibility, but where you go for the genetic test depends on whether you’re currently pregnant or your child has already been born. During pregnancy, an amniocentesis or a CVS testing can reveal whether your child is at a higher risk.
After birth, the same type of DNA testing, including those from an at-home kit, can show whether your child is a carrier.
It’s important to note that the presence of the longer protein does not indicate that your child will develop the disease, simply that they are a carrier and can pass it on to their children.
If you’re looking for more information about how the carrier status can affect your child in the future or how it can affect your future pregnancies, it’s a good idea to sit down with a genetic counselor.
DNA Testing for Huntington’s Disease: Strengths and Limitations
As with all types of DNA testing, there are certain strengths and limitations that come along with the results. For example, knowing whether you’re a carrier makes it easier to prepare for the future and to educate yourself on the disease and its symptoms.
However, there’s also the downside of DNA testing which is uncertainty. Most diseases and medical conditions come with a risk factor, never a certainty that you’ll develop the condition. So, if you test positive or your child tests positive for the longer huntingtin protein, there’s no concrete answer as to whether or not the possibility of the disease will become a reality.
What Are the Chances That I Will Pass Huntington’s Disease on to my Child?
If you’re a carrier or you have a long family history of Huntington’s disease, it’s only natural to worry about whether you’re going to pass it down to your children.
The HD gene is an autosomal dominant pattern gene, as opposed to recessive, which means that only one parent has to have the condition or be a carrier for it to be passed on.
With Huntington’s, if one parent is a carrier, or has the disease, there’s a 50 percent chance that he or she could pass it onto their child 6.
If I Have One Child with Huntington’s Will All my Children Have it?
No, the DNA game is much like roulette. Some children will inherit the expanded protein that causes the disease, while others will not have it at all. There’s no way to determine whether the child will inherit the HD gene, with the exception of testing the sex cells before in-vitro fertilization.
Testing for Huntington’s Disease on a Pregnancy or Before a Pregnancy is Achieved
If you plan on having children or are pregnant, the unknown can be very worrisome. This is especially true if you’re a carrier or you have a long history of Huntington’s in the family.
Fortunately, there are a few ways you can test both before and during pregnancy.
For women who are already pregnant, there are two options: you can get tested through an amniocentesis, or you can wait until the baby’s born to have a blood sample collected and tested. After birth, a blood sample is the only way to determine if the abnormal HD gene exists.
For women who are trying or thinking about trying to get pregnant, you and your partner can choose to undergo genetic testing with a genetic counselor before pregnancy is achieved. This will let you know what potential diseases or conditions you’re both a carrier of, and what the risks are for passing them onto your future children.
Who Does Huntington’s Disease Typically Affect?
Huntington’s is not a discriminatory disease, meaning it doesn’t target one gender or a specific age group, though most are between the ages of 30 and 50 during the onset of symptoms 7.
Males and females alike are at risk, depending on whether they carry the abnormal gene.
Does Huntington’s Disease Occur in Children?
Huntington’s is very rare in children, and it is not something that happens in young children. If it occurs in children, it’s typically onset in the late teens and early 20s. This is known as juvenile Huntington’s disease and it progresses much quicker than if it was onset in adults.
Huntington’s Disease Treatment Options
Is Huntington’s Disease Treatable?
The disease itself is not treatable, but the symptoms that present after onset are mostly treatable. Despite its fatal nature, doctors still aim to make patients as comfortable as possible during the years that they live after diagnosis.
Because it affects different aspects of a person’s body, there are numerous treatments that doctors may try including, but not limited to:
- Huntington’s chorea, which is uncontrollable body movements, is often treated with physical therapy and tetrabenazine, though antipsychotic drugs are an option should tetrabenazine not work.
- Antidepressants, mood stabilizers and antipsychotics medications are commonly administered to help with psychiatric disorders caused by Huntington’s wherein patients can’t control emotional and cognitive changes.
- Psychotherapy, speech therapy and occupational therapy can all help improve quality of life and limit the amount of outside help a person with the disease needs.
Not all treatments work for all patients. Your doctor will prescribe specific treatments as they see fit as your symptoms progress.
The Prognosis for Huntington’s Disease
Currently, the prognosis for Huntington’s is always fatal, but research is helping doctors make headway in treating the symptoms of those diagnosed with the disease.
These treatments help patients live longer lives with more functionality.
Does Huntington’s Disease Go Away?
No, Huntington’s is a lifelong disease that eventually results in the death of the person who has it. While there is no cure, researchers are looking at improving treatment methods to lengthen the lifespan of patients with the disease.
With access to the Genetic Testing Registry (GTR), it’s possible to learn more about the disease.
What Are Huntington’s Disease Care Options?
During the early and middle stages of the disease when the symptoms are still pesky but not overwhelming, medical treatments such as drugs and therapies can help patients maintain their independence.
However, once the disease hits the late stage, patients will likely need ongoing care either in the home or at a qualified facility.
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U.S. National Library of Medicine. Medline Plus. 2019. ↩
- George Huntington (1850-1916) and hereditary chorea.
Lanska DJ. J Hist Neurosci. Apr 2000. ↩
- A survey-based study identifies common but unrecognized symptoms in a large series of juvenile Huntington’s disease. Amelia D Moser, Eric Epping, Patricia Espe-Pfeifer, Erin Martin, Leah Zhorne, Katherine Mathews, Martha Nance, Denise Hudgell, Oliver Quarrell & Peg Nopoulos. Published Online 18 Oct 2017. ↩
- Gene Therapy Stalls Development Of Huntington’s Disease In Mice. California Institute of Technology.
sciencedaily.com. 09 November 2009. ↩
- Searching for the Secrets of Huntington’s Disease.
Neta Zach. haaretz.com. 05/12/2001. ↩
- When Huntington’s Disease Runs in Your Family.
Britni R. McAshan. tmc.edu. 04 November 2016. ↩
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mind.uci.edu. 2019. ↩