Overview

Huntington’s disease, also known as HD, is a progressive degeneration of nerve cells in various areas of the brain causing them to die over the span of time due to lack of or malformation of the huntingtin protein. HD is an inherited disease based on genetic factors and most commonly presents symptoms in middle-aged adults, however in rare cases, is possible in children, known as juvenile HD. Symptoms vary from physical impairments of movement and abilities to difficulties with cognitive function, which are all based on the severity and progression of the disease.

What is huntingtin and does its function correlate with symptoms of HD?

The huntingtin protein is formed by a code of DNA consisting of the base pair sequence: CAG. Extensive repeats in this sequence result in HD. Despite the overall function being unknown, it is suspected it is necessary for chemical signaling and protecting the cell from apoptosis (self-destruction). Apoptosis occurs in the mutated form of huntingtin due to the clumping of the protein in areas of the brain which kills the nearby cells causing further degeneration. Deficits to chemical signaling in pathways and degeneration of nerve cells within the brain can be linked to the cognitive impairments seen among individuals such as difficulties with memory, thought, and attention. (HTT gene, Medline Plus)

Which area of the brain is associated with motor symptoms?

The overall symptoms of HD are variable by each individual and will change over time as the disease progresses. The disease can impact the basal ganglia, specifically the striatum, which is responsible for coordination and movement. Damage to the basal ganglia in the sense of HD results in tremors, chorea (uncontrolled movements), and akinesia (becoming rigid and stiff), which over time will also produce difficulty in walking. (National Institute of Neurological Diseases)

Which area of the brain is associated with cognitive symptoms?

HD also impacts the cerebral cortex, which is in charge of thought, perception, consciousness, and memory. Cognitive symptoms include attention deficits, insomnia, difficulty with judgment and problem-solving, formation and verbalizing clear thoughts, and increased risk of dementia. (National Institute of Neurological Diseases)

Treatments

Unfortunately, there is no cure or treatment to stop or reverse the symptoms of HD. Drug-specific therapy can be used to treat and minimize the effects of certain symptoms such as tetrabenazine used to treat chorea. In some cases, antipsychotics are used to control hallucinations, delusions, or violent outbursts due to changes in mood regulations. Commonly, antidepressants and antianxiety medications are prescribed over time due to symptoms caused by HD. (National Institute of Neurological Diseases)

CAG repeats	HD Present
<27	No
27-35	unlikely, but can pass on
>36	Yes

Research

Current research methods involve understanding neurobiology by studying the gene’s details and using imaging to observe the physiological effects. Other methods involve the use of animal models to manipulate the brain to create symptoms of HD and monitor the progression or test treatments for the symptoms which is performed by a physiological psychologist. An example involved studying the effect on mice with HD when the mutation in reference to the glial cells which clean the brain of diseased neurons was suppressed which reduced the progression of the disease. New studies involve placing affected fetal tissue in non-human animals to understand possible ways of altering and replacing the lost functions at the cellular level. (genome.gov)