Huntington’s disease (HD) is an inherited neurological disorder in which nerve cells in parts of the brain gradually break down and die. Although there is currently no cure, doctors can treat some of its symptoms, and researchers are studying treatments aimed at slowing or preventing the underlying disease process. Here’s everything you need to know about it.
What is Huntington’s disease?
Huntington’s disease is caused by a change in the HTT gene, which carries instructions for producing the protein huntingtin. The abnormal gene contains excessive repeats of a three-base DNA sequence called CAG (cytosine, adenine, and guanine).
According to the National Institutes of Health (NIH), most people have fewer than 27 CAG repeats and are not at risk for developing HD. People with 27–35 repeats are unlikely to develop the disease, but they may pass the expanded repeat to their children. People with 36 or more repeats may have disease-causing expansion.
The abnormal huntingtin protein can become misshapen and damage brain cells. The basal ganglia, a group of brain structures involved in the coordination of movement, and the cerebral cortex, which plays a role in thinking, perception and memory, are among the most affected areas, according to the NIH National Human Genome Research Institute.
HD is an autosomal dominant disorder. This means that a person only needs one copy of the altered gene to develop the disease. Each child of a parent who carries the HD gene has a 50% chance of inheriting it. If a child does not inherit the altered gene, they will not develop HD and will not pass the gene on to their children.
What are the symptoms?
Symptoms of Huntington’s disease vary from person to person and usually become more severe as the disease progresses. Broadly speaking, they include movement, thinking and behavior or mood.
According to the NIH, one of the most recognizable movement symptoms is chorea—uncontrollable dance movements that can affect the fingers, feet, face or torso. These movements may worsen when the person is nervous or distracted.
Early symptoms may include mild clumsiness, problems with balance or movement, difficulty walking, stiff or stiff muscles, involuntary shaking or tremors, and dystonia, in which muscles involuntarily tense and the body may be locked in unusual positions. Unusual eye movements may also occur in the early stages of the disease.
As the disease progresses, people may have problems speaking, swallowing, and eating. Difficulty eating and swallowing can lead to weight loss, choking, and lung infections. Other physical symptoms include fatigue, lack of energy, trouble sleeping and, in some cases, seizures.
HD also affects cognitive abilities. People may have difficulty concentrating, making decisions, solving problems, assessing situations, organizing or prioritizing tasks, learning or remembering new information, or expressing their thoughts in words. These problems can gradually interfere with work, driving, and the ability to care for oneself.
Behavior and mood may also change. Symptoms may include irritability, mood swings, depression, anger, loss of interest, and withdrawal from friends and family. Severe depression, suicidal ideation, and psychosis may occur.
How is it diagnosed?
Doctors diagnose headache by taking into account a person’s symptoms, family history and neurological examination, supported by laboratory and genetic tests and, if necessary, brain imaging.
A neurologist may evaluate reflexes, balance, movement, muscle strength, walking, hearing, thinking, memory, and mood. Other professionals, including mental health professionals, genetic counselors, and speech therapists, may also be involved in diagnosis and treatment.
The most accurate way to confirm HD is a genetic test. The blood sample is used to analyze the DNA and determine the number of CAG repeats in the HTT gene. The accompanying material from the National Institutes of Health notes that people with 36 or more repeats have a disease that causes expansion, while people with fewer than 26 repeats do not have the disease.
MRI and CT scans can reveal structural changes in the brain as headache progresses, including shrinkage of affected areas. However, such changes can also occur in other conditions, and scan results may be normal in people with early stage HD. Thus, traditional brain imaging is not a substitute for genetic testing to confirm the disease.
Recent research suggests that a new type of MRI technique may eventually allow researchers to see more than just shrinking brain size and gain an indirect picture of the cellular damage caused by HD.
According to TalkThe researchers used soma and neurite density imaging (Sandi), a diffusion MRI technique, to assess cellular changes in the brains of 56 people with HD and 57 healthy volunteers.
In the basal ganglia of HD patients, scans showed lower apparent density of cell bodies, larger cell bodies, and more space between cells—changes reminiscent of those seen in postmortem brain tissue.
The measurements were also associated with disease severity and motor activity, and in some areas of the striatum helped explain up to 63% of the observed brain shrinkage. Researchers say Sandy could eventually help track disease progression and evaluate whether treatments protect brain cells, but larger, longer-term studies are needed before it can be used clinically.
What are the treatment options?
According to the US National Institute of Neurological Disorders and Stroke, there is currently no treatment that can stop or reverse HD. Treatment is aimed at eliminating symptoms and improving quality of life.
For chorea, medications including tetrabenazine, deutetrabenazine, and valbenazine can be used to affect brain signals involved in controlling movement.
Antipsychotic medications, including risperidone and olanzapine, may help reduce chorea as well as psychiatric symptoms such as severe irritability, unusual thoughts, or hallucinations. However, some antipsychotic drugs may worsen movement-related symptoms, so doctors need to monitor patients and adjust treatment if necessary.
Medications can also be used to treat depression and anxiety. Treatment may have side effects such as fatigue, drowsiness, difficulty concentrating, anxiety, or increased activity. Beyond symptom management, research is increasingly focusing on finding ways to modify the underlying disease.