The Facts
Huntington's disease, also called Huntington's chorea, is a hereditary condition that affects the brain, specifically an area called the basal ganglia (located deep in the brain).
The disease follows an autosomal dominant pattern of inheritance, meaning that if one parent has the disease, each child has a 50% chance of inheriting it. Huntington's disease is quite rare, occurring in about 4.9 per 100,000 people worldwide; 6.4 per 100,000 in Europe; 8.8 per 100,000 in North America; and 2.4 per 100,000 in Asia. Both males and females are affected equally.
The disease destroys nerve cells (neurons) in parts of the brain resulting in lower levels of chemicals called neurotransmitters that carry signals in the brain. People with this disease experience uncontrolled movements, loss of mental abilities, and changes in personality or behaviour.
Causes
Huntington's disease is caused by mutations in a gene which produces a protein called huntingtin. The role that this protein plays in normal brain function is not well understood.
Symptoms and Complications
The onset of the disease is slow and subtle. The first symptoms usually begin in the fourth or fifth decades of life although occasionally they may start in childhood or be delayed into the 60s.
In the early stages of the disease, personality changes such as depression, dementia, or other psychiatric changes may be noticed. This sometimes happens before or at the same time as movement disorders. Abnormal motions start on one side of the body, commonly affecting the face and arms. Symptoms include facial movements that look like mild grimacing and speech problems. When the person becomes emotionally upset, symptoms tend to worsen and become more severe.
As the disease progresses, abnormal movements become faster – almost violent – and purposeless. Patients tend to display jerky, almost dance-like motions (chorea). There is often severe dementia associated with this late stage of the disease.
Eventually, people with this disease are unable to look after themselves and need help with daily activities and functions such as eating, hygiene, and toileting. People tend to become bedridden and may suffer complications such as congestive heart failure and pneumonia. People diagnosed with adult-onset Huntington’s disease usually live about 10 to 20 years after diagnosis.
Making the Diagnosis
During a physical exam, a doctor will look for irregular and uncontrolled movements and signs of muscle deterioration or reduced mental or intellectual function. A family history of the disease will help diagnose Huntington's disease, and DNA analysis will detect genetic defects.
Other possible tests include computed topography (CT) or magnetic resonance imaging (MRI) scans to look for areas of the brain (caudate nucleus) that may have atrophied (decreased in size).
Treatment and Prevention
Because there is no cure for this disease, treatment aims to lessen the severity of symptoms and make people comfortable. Medications are usually given to help control abnormal muscle movements, including tranquilizers, benzodiazepines, neuroleptics, and medications that work on the nervous system such as tetrabenazine*. Antidepressants may be used to treat depression, if present. Psychosis and behavioural problems can be treated with a class of drugs known as antipsychotics. Management of mood disorders can also help decrease chorea.
Because of the delayed onset of symptoms, the disease can be transmitted to children before you even know you have it. If you have a family history of Huntington's disease, you may want to consider genetic testing before deciding to have children. An experienced genetic counsellor can help guide you through the many complex issues involved in making the best decision for you.
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