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Chorea comes from the Greek word for dance. It refers to the uncontrolled movements that are a main symptom of HD. The illness has been traced back at least as far as the Middle Ages. But it was named by George Huntington, an American healthcare provider, in 1872. The illness also has been called chronic progressive chorea. This means that symptoms get worse over time.

HD causes certain brain cells called neurons to die. Over time, this affects the way a person feels, thinks, and moves. The death of the neurons causes jerky movements (chorea) and dementia.

A genetic defect causes the brain to make an abnormal version of a protein called huntingtin. This protein affects neurons in parts of the brain that control movement and thought, destroying them. Researchers are still trying to learn how the abnormal huntingtin protein interferes with normal cell activity.

HD most often strikes in midlife, but it can also show up in children and in older adults. About 15,000 people in the U.S. have HD. And 150,000 have a 50% risk of developing it. HD cases are found worldwide.

A single abnormal gene on chromosome number 4 causes HD. Chromosome number 4 is one of the 22 chromosomes that aren't linked to gender. This means both men and women have equal chances of inheriting HD (called autosomal inheritance). If a child does not inherit the HD gene, the child will not develop HD and can't pass the gene on to later generations. If the child inherits the gene, that child will eventually develop HD. If 1 child in the family inherits the gene, it does not make it more or less likely that other children in the family will inherit the gene.

Other early symptoms include trouble with driving, remembering facts, or making decisions. Also uncontrolled movements of the feet, hands, face, or trunk. The earlier the symptoms appear in a person's life, the faster the disease tends to progress. As the disease gets worse, the person finds it harder and harder to concentrate. Emotional disturbances such as anger or depression may ease or may become more pronounced. Uncontrolled movements become worse, and coordination and balance are affected. Talking, swallowing, eating, and controlling bladder and bowel function may become difficult.

A brain imaging test may also be ordered for diagnosis. For those at risk of developing HD, a blood test is also available to see if the HD gene has been inherited. Not all people at risk choose to have this test.

There is no way to stop the progression of HD. But medicine can help control the movement problems and emotional difficulties of people with HD. These medicines can come with unpleasant side effects, including severe tiredness (fatigue), restlessness, and over-excitability. Daily exercise is important for people with HD, because those who exercise tend to feel better than those who do not. Getting good nutrition and enough fluids are also important to prevent weight loss and dehydration.