Juvenile Huntington’s disease (JHD) is the name given to Huntington’s disease (HD) that declares itself before the patient is 20 years of age. It accounts for roughly 5 to 10 percent of all Huntington’s disease cases, and like Huntington’s, it is hereditary and neurodegenerative.

JHD is characterized by uncontrolled movements, loss of intellectual abilities, and emotional disturbances. One common sign of juvenile Huntington’s is a rapid decline in school performance.

What causes JHD?

JHD it is a progressive disorder that leads to the breakdown of cells in certain areas of the brain, particularly those of the frontal lobe that controls behavior and higher thinking.

It is caused by the same genetic defect in the huntingtin gene that causes Huntington’s disease, a defect called a CAG repeat expansion. The length of the CAG repeat expansion inversely correlates with the age of onset of the disease. In other words, the longer the repeat, the earlier the disease onset. Most JHD patients usually have between 80 and 100 CAG repeats (the gene normally has 35 or fewer CAG repeats).

Juvenile HD is inherited in an autosomal dominant manner, meaning one copy of the mutated gene — from either parent, although from the father is most common — can cause the disease in a child.

How does JHD affect the body?

Like HD, JHD can affect movement, emotions, and thinking ability.

Movement

A young person with JHD may begin to walk on their toes or develop a stiff-legged or scissored gait. They may become more clumsy, and tend to lose their balance and fall more often. As the disease progresses, patients may experience difficulties with chewing and swallowing as well as speaking.

Emotions

The loss of abilities and independence that a child or adolescent with JHD experiences can cause emotional responses, such as feelings of frustration, anger, sadness, fear, and grief. Obsessive thoughts or irrational fears can occur, and they may lead to aggressive behavior. Families affected by JHD can request emotional support from a number of sources.

Thinking ability

Children may begin to struggle when performing familiar tasks, such as writing, reading, and counting. Learning new information and forming new memories can also become increasingly difficult.

Puberty

Puberty may be particularly challenging in children with JHD, because natural changes in teenagers’ bodies heighten the sex drive and the need for independence.  JHD affects their ability to control these natural behaviors and urges.

How is JHD diagnosed?

A specialist, typically a neurologist, may have to see a child several times before establishing the presence of neurological symptoms. A complete and accurate family history helps greatly in reaching a diagnosis. When JHD is suspected, a genetic test on a blood sample will be requested to confirm the diagnosis.

How is JHD treated?

There is currently no cure for any form of Huntington’s disease. Treatment is supportive and focuses on improving patients’ quality of life. While symptoms can vary greatly from one patient to another, the average life expectancy for children and youth with JHD after diagnosis is roughly 10 years. Developments in research continue to provide hope that better treatments are within reach.

Adult vs. juvenile Huntington’s disease

Children or youth with JHD often only have mild chorea (involuntary jerky movements of the arms, legs, trunk, neck, or face) or none at all. Rather, they tend to become more rigid and stiff. Epileptic seizures occur in about 25 percent of all juvenile HD cases, and are very rare in adults with Huntington’s.

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