About Huntington's Disease and Related Disorders
A Brief History of Huntington's Disease
Huntington's disease (HD) is named after George Huntington, who described it among residents of East Hampton, Long Island in 1872. It is a hereditary neurodegenerative disease. In 1993, a collaborative group of investigators discovered the gene that causes HD. As a result of this discovery it is now possible to diagnose HD with blood or tissue samples.
The Genetic Cause of HD
HD is caused by mutation in a gene located on chromosome 4. This gene is found in every human being, and contains a CAG repeat sequence. We have not yet discovered the gene's normal function. In a case of HD, the gene contains an abnormally large number of CAG repeats. The larger the number of triplet repeats, generally speaking, the earlier in life one will develop HD. Furthermore, when the gene is passed from father to child (but not when passed from mother to child) the gene may lengthen even more, resulting in an earlier age of onset for the disease. This phenomenon is known as anticipation.
Genes for diseases can be either dominant or recessive. The gene for HD is dominant. Each child of an affected parent has a 50/50 chance of getting the mutant gene, and therefore has a 50% chance of inheriting the disease. On the other hand, if people with a parent suffering from HD do not inherit the mutant gene, they cannot pass it on to anyone else.
It is important to understand that while people are born with the mutated gene for HD, in most cases they will not develop the symptoms until later in life. Therefore someone can be without symptoms or presymptomatic for a number of years. In the past, there was no way to test for the abnormal gene, but now a blood test can determine whether or not an individual carries the gene for HD. This test can be used in cases of suspected HD, to confirm the diagnosis, or it can be used as a predictive test in individuals who are at risk for HD. People who are at risk may want to undergo predictive testing in order to put their minds at ease, to plan for their medical needs, or prior to having children. The decision to have such a test is a momentous one and should not be taken lightly. Most centers that do predictive testing, including ours, require a period of counseling before and after the test.
What Are the Characteristics of HD?
Onset is usually in mid-life, but can occur any time from childhood to old age. The initial signs of this disorder may be subtle. HD is characterized by a movement disorder, dementia, and psychiatric disturbances. Additional characteristics of HD include personality changes, weight loss (probably from a combination of difficulty eating, and calories burned by the involuntary movements), difficulty swallowing, and hard-to-understand speech.
The Course of HD
Once an individual develops signs of HD the course of the disease can last anywhere from ten to thirty years. Typically, the course of HD can be roughly divided into three stages.
In this stage patients can still perform most of their usual activities. They may still be working and may still be able to drive. Involuntary movements are mild and infrequent, speech is still clear, and dementia, if present at all, is mild.
At this stage patients are more disabled and may need assistance with some of their activities of daily living. Falls, weight loss, and swallowing difficulties may become a problem. Dementia is more obvious to the casual observer. Involuntary movements are more pronounced.
Patients entering this stage of the disease require almost total care and may reside in hospitals or nursing homes, although some remain at home. They may no longer be able to walk or speak. They may be more rigid now and show fewer involuntary movements. Individuals in this stage may or may not be able to swallow food. At this stage most patients do not seem to suffer much as they are apparently unaware of their surroundings. When the patient passes away, the cause of death is usually related to malnutrition, pneumonia, or heart failure.
What Treatments Are Available?
At this time, there is no cure for HD. Researchers are working on a number of treatments that may slow down the progression of the disease. There are a number of interventions available today that improve the quality of life for HD sufferers. In the early and middle stages of the disease, medications can be given in small doses to HD patients to help suppress the involuntary movements. Depression and other psychiatric conditions in people with HD can be quite effectively treated. Proper nutrition, exercise and precautions in the home can help minimize many of the potential consequences of HD such as weight loss, falls, and choking on food. Finally contact with other HD sufferers, family members, and care-providers can be a vital source of support for HD patients and their families.
People with HD should discuss their concerns and wishes about treatments/interventions (e.g. feeding tubes, resuscitation requests) and autopsies with their families and doctors while they are still able to speak for themselves.