Huntington’s disease (HD) is an inherited disorder causing the progressive degeneration of nerve cells in the brain. This neurodegenerative condition impacts an individual’s movement, mood, and cognitive function. Many people wonder if HD is a type of dementia, similar to Alzheimer’s disease. HD is a complex disorder affecting multiple systems simultaneously, presenting a clinical picture that extends beyond cognitive decline alone.
Defining Huntington’s Disease and Dementia
Dementia describes a loss of cognitive functioning—such as remembering, thinking, and reasoning—severe enough to interfere with daily life. Huntington’s disease (HD) is a specific, inherited disease caused by a genetic mutation. HD is a distinct neurological condition that invariably causes dementia as it progresses.
The cognitive decline in HD fits the broad definition of dementia, as the impairment is significant and affects functional independence. This cognitive state is one of the three primary symptom categories of the disease. The severe decline in thinking and reasoning skills is classified as a form of dementia, but the specific pattern of deficits sets HD apart from other syndromes.
Cognitive Symptoms Unique to Huntington’s Disease
The dementia associated with HD is classified as subcortical, arising from damage to deep brain structures, particularly the basal ganglia. This contrasts with cortical dementias, like Alzheimer’s disease, which primarily affect the cerebral cortex. The difference in affected regions leads to distinct cognitive profiles.
A hallmark of HD is executive dysfunction, involving difficulty with complex tasks like planning, organizing, and sequencing. Individuals often struggle with decision-making and judgment. Another prominent feature is bradyphrenia, a marked slowing of thought processing and mental speed.
Memory impairment in HD follows a subcortical pattern. Individuals may struggle to retrieve learned information, but their ability to encode new memories remains relatively intact until later stages. This differs from the severe, early memory loss seen in cortical dementias. Impaired attention and concentration are also common, making it challenging to focus on intellectual tasks.
The Non-Cognitive Signs of Huntington’s Disease
HD is recognized by a triad of symptoms: cognitive, psychiatric, and motor. The non-cognitive signs help distinguish it from other dementia syndromes. The most visible motor symptom is chorea, characterized by involuntary, jerky, “dance-like” movements affecting the face, trunk, and limbs.
As the disease advances, the hyperkinetic movements of chorea can be replaced by hypokinetic symptoms, such as rigidity and dystonia. these motor issues severely impact daily life, causing difficulty with balance and gait, and increasing the risk of falls. Swallowing (dysphagia) and speech (dysarthria) become progressively impaired due to lack of muscle control.
Behavioral and psychiatric changes are often the earliest signs, sometimes appearing years before motor symptoms begin. Common psychiatric issues include depression, anxiety, and apathy, which is a loss of motivation. Irritability, aggression, and obsessive-compulsive behaviors are also reported. This combination of motor and psychiatric symptoms alongside cognitive decline highlights the widespread impact of HD.
Genetic Basis and Therapeutic Approaches
Genetic Basis
Huntington’s disease is caused by a mutation in the Huntingtin gene (HTT) on chromosome 4. This is an autosomal dominant disorder, meaning inheriting one copy of the faulty gene results in the disease, giving each child a 50% chance of inheritance. The mutation involves an abnormal expansion of a trinucleotide repeat sequence called Cytosine-Adenine-Guanine (CAG).
A normal HTT gene typically has 10 to 35 CAG repeats, but in HD, this sequence is repeated 40 or more times. This leads to the production of a toxic, mutated huntingtin protein. The number of CAG repeats is inversely correlated with the age of symptom onset; a higher number of repeats predicts an earlier onset.
Therapeutic Approaches
While there is currently no treatment to stop or slow the underlying neurodegeneration, management focuses on alleviating the diverse range of symptoms.
Motor symptoms like chorea are often managed with medications that affect dopamine signaling, such as vesicular monoamine transporter 2 (VMAT2) inhibitors (e.g., tetrabenazine or deutetrabenazine). Psychiatric symptoms are addressed using standard pharmacological approaches, including antidepressants for depression and anxiety, and antipsychotic medications for irritability or psychosis. A multidisciplinary care team, including physical, occupational, and speech therapists, helps individuals maintain function and quality of life as the condition progresses.