Huntington’s disease

Huntington’s Disease
Huntington’s disease is an autosomal dominant disorder, which is found on the # 4 chromosome. George Huntington discovered it in 1872. It mainly has an effect on the nervous system. There are around 210,000 bases between D4S180 and D4S127. The disease itself is found in 2% of people in their childhood, and in 5% of the people they were older then 60. (Miller p 16) In the majority of the affected people the disease is detected between the ages of 35-45. In males the disease begins around the time of their childhood. However, in females it begins later in life. This severe symptom has a tendency for the condition to worsen as it is passed on from generation to generation. Huntingtons disease is paternally inherited and new mutations are rare (about 1%). (Encarta Encyclopedia)
The basic biochemical defect has not yet been discovered. There is a high amount of quinolinic acid, a neurotoxin normally present in the brain. Quinolinic acid may be killing receptors. These receptors are known targets of quinolinic acid. The gene encodes an amino acid protein called huntington. The protein does not show any resemblance to other proteins. Scientists are also finding it difficult to detect differences in peoples gene movement who are and are not affected by the disease. The enzyme huntington binds to glyceraldehydes-3-phosphate-dehydrogenase (GAPDH), a important enzyme in glycolysis. The cells now have inefficient glucose to the cells, which in the overall process causes the cells to die. ( Science News p268 )
Symptoms that may be expressed include memory loss, mood swings, slurred speech, depression, and death usually from heart disease or pneumonia. There can also be steady downfall of the person mental health. This also can destroy two small regions of the brain (the putamen and the caudate nucleus) that help control movement.

If the disease is of the homozygous variety in a person it occurs in 1 in every 10,000 people. If the disease is heterozygous then in is found between 1 in every 5,000 people and 1 in every 15,000 people. It is more common in Venezuela then anywhere else, although it is discovered in about 240 people per year in the United States. A DNA marker G8 (D4S10) is closely linked to HD and has been identified as being on the # 4 chromosome and can detect Heterozygotes. (Encarta Encyclopedia) The connection between G8 and HD has not been clinically used because its a very serious disease. Theoretically a homozygote can be detected parentally. If a female has a child and she is tested positive for HD and ahs no history of it then the father as well as the child a bound to end up with the disease. (Textbook of Medical Physiology)
There has not yet been a successful use of any drug to completely stop the progression of the disease. However, drugs such as diazepam help a person with HD feel more relaxed and helps with their movement disorder. The prognosis for a person with HD is usually death 20 or so years after it commences. Although some of the causes of death are suicide, or death by congestive heart failure or pneumonia. (
Encarta Encyclopedia
Sci News 11/12/83 – p. 311 genetic marker for HD
Sci News 4/23/88- p. 268 Experimental Cell grafts for HD; blocks quinolinic acid damaging for brain
Textbook of Medical Physiology 1996 p. 729 Huntingtons disease

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