What is Huntington's Disease?
Huntington's Disease (HD) is a brain disorder that affects a person's ability to think, talk, and move.
The disease destroys cells in the basal ganglia, the part of the brain that controls movement, emotion, and cognitive ability. HD is caused by a mutation in a gene on chromosome 4. The job of its protein product, huntingtin, is to direct the delivery of small packages (vesicles containing important molecules) to the outside of the cell. Normally, the coding region of this gene contains the DNA sequence "CAG" repeated again and again. The number of times this triplet is repeated varies from person to person, ranging from 10 to 26 times. People with HD have an abnormally high number of these CAG triplets, approximately 40 or more. This likely disrupts the function of the gene's protein product, but how the expansion of the CAG repeat causes disease is unknown. Somehow the brain cells of HD patients accumulate clumps of protein that become toxic, resulting in cell death. Some patients lose more than 25% of their brain cells before they die.
How do people get Huntington's Disease?
Huntington's disease is inherited in an autosomal dominant pattern. This means that everyone who inherits the faulty gene will eventually get the disease. A parent with a mutation in the HD gene has a 50 percent chance of passing the disease to their children.
What are the symptoms of Huntington's Disease?
Huntington's disease affects the part of the brain that controls thinking, emotion, and movement. Most people who have the disease start to see symptoms between the ages of 30 and 50 (but symptoms can appear earlier or later in life). The disease gets worse over time.
Symptoms include poor memory, depression and/or mood swings, lack of coordination, twitching or other uncontrolled movements, and difficulty walking, speaking, and/or swallowing. In the late stages of the disease, a person will need help doing even simple tasks, like getting dressed.
How do doctors diagnose Huntington's Disease?
During pregnancy, a woman can find out if her baby will have the disease with two tests: (1)taking a sample of fluid from around the fetus (amniocentesis), or (2)by taking a sample of fetal cells from the placenta (chorionic villus sampling (CVS)).
After the child is born, doctors can identify the disease by first doing a series of neurological and psychological tests. A genetic test can then confirm the diagnosis by determining if the person indeed has inherited the HD gene mutation (an expansion of the CAG triplet). However, the test cannot tell at what age a person will begin to get sick. Some question whether it is ethical to do the genetic test before symptoms appear. However, others wish to know their status before deciding to have children.
How is Huntington's Disease treated?
Treatments do not slow the progression of the disease, but they can help make the patient more comfortable. Medications ease feelings of depression and anxiety; others control involuntary movements. Physical or speech therapy helps HD patients lead more normal lives.
Interesting facts about Huntington's Disease
The disease was named for Dr. George Huntington, who first described it in 1872.
In the United States, about 1 in every 30,000 people has Huntington's disease.