What Is Huntington’s Disease?
Huntington’s disease is a rare neurological disorder that primarily affects movement, thinking, and mental health. It can begin at any age, but symptoms most commonly appear between the ages of 30 and 40. When the disease develops before the age of 20, it is classified as Juvenile Huntington’s Disease (JHD). In these cases, symptoms may differ from the adult form and often progress more rapidly.
Why Is It Called a “Chorea” Disease?
The most distinctive feature of Huntington’s disease is a movement disorder known as chorea. Chorea refers to involuntary, irregular movements that often affect the arms, legs, face, and tongue.
These choreatic movements may include involuntary jerking or writhing motions, muscle rigidity or contractures, slow or abnormal eye movements, difficulty walking or maintaining posture and balance, and problems with speech or swallowing. When combined, these movements can resemble a form of uncontrolled dancing (Figure 1), which is why the disease is commonly referred to as “Huntington’s chorea.”
Figure 1. Chorea
Figure 2. Basal Ganglia
How Does Huntington’s Disease Begin?
In people with Huntington’s disease, the seeds of the condition are present from birth. Individuals are born carrying an expanded number of CAG repeats in the HTT gene, yet symptoms usually do not appear immediately. The length of this CAG repeat expansion is directly linked to Huntington’s disease: in general, a higher number of repeats is associated with an earlier age of onset and more severe symptoms.
Huntington’s disease is closely associated with structural changes in the brain, many of which begin silently years before symptoms become apparent. The earliest brain regions affected are the basal ganglia (Figure 2), and more specifically the caudate nucleus and the putamen (Figure 3). These structures play a critical role in suppressing unwanted movements and function as the brain’s braking system for motor control.
As neurons within these regions begin to degenerate, movement becomes increasingly uncontrolled, while emotional regulation and judgment are also compromised.
Figure 3. Diagram of the caudate nucleus and putamen
Why Is Huntington’s Disease Often Misdiagnosed?
Although the most recognizable feature of Huntington’s disease is the uncontrolled, dance-like movements, these are rarely the initial clinical signs.
In the early stages, Huntington’s disease primarily presents with psychiatric and behavioral changes, including irritability, anxiety, depression, impaired impulse control, and declining attention and planning abilities. These early symptoms are often misattributed to other psychiatric conditions, such as bipolar disorder or schizophrenia.
As a result of this early misdiagnosis, patients are frequently prescribed antipsychotic medications, such as chlorpromazine (Thorazine). While these medications can help manage psychiatric symptoms, they are also associated with side effects. One notable adverse effect is tardive dyskinesia, which is characterized by involuntary spasms or choreiform movements involving the tongue, lower face, jaw, and limbs.
Because the motor manifestations of tardive dyskinesia closely resemble the chorea that appears in the later stages of Huntington’s disease, the movement symptoms that emerge over time may be mistakenly attributed to medication side effects rather than to the progression of Huntington’s disease itself. As a result, the underlying condition remains unrecognized, and patients often miss the opportunity for accurate diagnosis and early intervention.