Juvenile Huntington’s disease (JHD) is the name given to Huntington’s disease that is recognized before the patient is 20 years old. It accounts for roughly 5% to 10% of all Huntington’s disease cases, and is hereditary and neurodegenerative, like the adult form.
Juvenile Huntington’s is characterized by muscle contractions and stiffness, loss of intellectual abilities, and emotional disturbances. One common sign of juvenile Huntington’s is a rapid decline in school performance.
Juvenile Huntington’s 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 juvenile Huntington’s patients usually have more than 50 CAG repeats (the gene normally has 35 or fewer repeats). However, not everyone with a high CAG count develops juvenile Huntington’s and less than 10% of those with a faulty huntingtin gene will have more than 50 CAG repeats.
Juvenile Huntington’s is inherited in an autosomal dominant manner, meaning one copy of the mutated gene — from either parent, although inheritance is more likely to be from the father — can cause the disease in a child.
Like Huntington’s in adults, the juvenile form can affect movement, emotions, and thinking ability.
Movement and seizures
A young person with juvenile Huntington’s may begin to walk on their toes or develop a stiff-legged or scissored gait. They may become clumsier, and tend to lose their balance and fall more often. As the disease progresses, patients may experience difficulties with chewing, swallowing, and speaking.
In contrast to adult patients, children often have only 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% of all JHD cases, and are very rare in adults with Huntington’s.
JHD patients’ loss of abilities and independence can cause emotional responses, such as frustration, anger, sadness, fear, and grief. Obsessive thoughts or irrational fears can occur, and they may lead to aggressive behavior.
Mood changes seem to be more common in people with juvenile Huntington’s versus those with the adult-onset disease.
Young patients 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 may be particularly challenging for children with JHD, because of natural adolescent changes that increase sex drive and the need for independence. The disease can affect their ability to manage these needs.
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 in reaching a diagnosis.
However, there are some juvenile Huntington’s cases in which the family history appears “normal” but in these cases, the parent may have died before experiencing symptoms or had not yet been diagnosed.
When juvenile Huntington’s is suspected, a genetic test can confirm the diagnosis.
With no cure currently for any form of Huntington’s disease, treatments can help manage symptoms to improve quality of life. While symptoms can vary greatly from one patient to another, the life expectancy for those with juvenile Huntington’s is 10 to 15 years after the onset of symptoms. Research continues in the search for better treatments.
Last updated: Oct. 20, 2021
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