Huntington's Disease Questions?

HD is called an autosomal dominant disorder because only one copy of the defective gene, inherited from one parent, is necessary to produce the disease. Individuals with juvenile HD usually inherit the disease from their fathers. These individuals also tend to have the largest number of CAG repeats. The reason for this may be found in the process of sperm production. Unlike eggs, sperm are produced in the millions. Because DNA is copied millions of times during this process, there is an increased possibility for genetic mistakes to occur. To verify the link between the number of CAG repeats in the HD gene and the age at onset of symptoms, scientists studied a boy who developed HD symptoms at the age of two, one of the youngest and most severe cases ever recorded. They found that he had the largest number of CAG repeats of anyone studied so far—nearly 100. The boy's case was central to the identification of the HD gene and at the same time helped confirm that juveniles with HD have the longest segments of CAG repeats, the only proven correlation between repeat length and age at onset.

A few individuals develop HD after age 55. Diagnosis in these people can be very difficult. The symptoms of HD may be masked by other health problems, or the person may not display the severity of symptoms seen in individuals with HD of earlier onset. These individuals may also show symptoms of depression rather than anger or irritability, or they may retain sharp control over their intellectual functions, such as memory, reasoning, and problem-solving.

There is also a related disorder called senile chorea. Some elderly individuals display the symptoms of HD, especially choreic movements, but do not become demented, have a normal gene, and lack a family history of the disorder. Some scientists believe that a different gene mutation may account for this small number of cases, bu this has not been proven.Early signs of the disease vary greatly from person to person. A common observation is that the earlier the symptoms appear, the faster the disease progresses.

Family members may first notice that the individual experiences mood swings or becomes uncharacteristically irritable, apathetic, passive, depressed, or angry. These symptoms may lessen as the disease progresses or, in some individuals, may continue and include hostile outbursts or deep bouts of depression.

HD may affect the individual's judgment, memory, and other cognitive functions. Early signs might include having trouble driving, learning new things, remembering a fact, answering a question, or making a decision. Some may even display changes in handwriting. As the disease progresses, concentration on intellectual tasks becomes increasingly difficult.

In some individuals, the disease may begin with uncontrolled movements in the fingers, feet, face, or trunk. These movements—which are signs of chorea—often intensify when the person is anxious. HD can also begin with mild clumsiness or problems with balance. Some people develop choreic movements later, after the disease has progressed. They may stumble or appear uncoordinated. Chorea often creates serious problems with walking, increasing the likelihood of falls.

The disease can reach the point where speech is slurred and vital functions, such as swallowing, eating, speaking, and especially walking, continue to decline. Some individuals cannot recognize other family members. Many, however, remain aware of their environment and are able to express emotions.

Some physicians have employed a recently developed Unified HD Rating Scale, or UHDRS, to assess the clinical features, stages, and course of HD. In general, the duration of the illness ranges from 10 to 30 years. The most common causes of death are infection (most often pneumonia), injuries related to a fall, or other complications.