Huntingtons Disease

Huntington’s Disease
Huntington’s disease, also known as Huntington’s chorea is a genetic disorder
that usually shows up in someone in their thirties and forties, destroys the
mind and body and leads to insanity and death within ten to twenty years. The
disease works by degenerating the ganglia (a pair of nerve clusters deep in the
brain that controls movement, thought, perception, and memory) and cortex by
using energy incorrectly. The brain will starve the neurons (brain cells), and
sometimes make them work harder than usual, causing extreme mental stress. The
result is jerky, random, uncontrollable, rapid movement such as grimacing of the
face, flailing of arms and legs, and other such movement. This is known as
chorea.


Huntington’s chorea is hereditary and is caused by a recently discovered
abnormal gene, IT15. IT stands for “interesting transcript” because of the fact
that researchers have no idea what the gene does in the body. Huntington’s
disease is an inherited mutation that produces extra copies of a gene sequence
(IT15) on the short arm of chromosome 4. A genetic base that exists in
triplicate, CAG for short, is effected by Huntington’s disease. In normal people,
the gene has eleven to thirty-four of these, but, in a victim of Huntington’s
disease the gene exists from anywhere between thirty-five to one-hundred or more.

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The gene for the disease is dominant, giving children of victims of Huntington’s
disease a 50% chance of obtaining the disease.


Several other symptoms of the disease exist other than chorea. High levels of
lactic acid have been detected in patients of Huntington’s disease as a bi-
product of the brain cells working too hard. Also, up to six times above the
normal level of an important brain brain protein, bFGF (or basic fibroblast
growth factor) in areas of the brain effected by the chorea. This occurs from
the problems on chromosome 4, where the gene for control of bFGF is also located.


As of yet, there is no treatment for Huntington’s disease. But with the
discovery of the mutated genes that cause it, there is now a way of diagnosing
if you will get it. This technique was discovered only recently and reported in
the Journal of American Medical Association in April, 1993. Something that many
people do not want to know. Because it can go two ways. Either you are extremely
relieved because the test shows up negative, and a great burdon is lifted off of
your mind, or you show up positive, and know how and a little bit about when you
will die, increasing the burdun very greatly. And living the rest of your life
in depression.


Some 30,000 Americans are currently suffering for this genetic disorder. Named
in 1872 for George Huntington the New York Doctor who first wrote down it’s
devestating symtoms, Huntingtons disease up to now was a silent time bomb.


13,000 people, the largest known concentration of sufferers from Huntington’s
Disease, live in the Lake Maracaibo region of Venezuela. The origins of this
gene pool has been traced back to the 1800’s to a woman named Maria Concepcion.

It was from blood samples of these people that scientists became extraordinarily
lucky and isolated the genetic marker that shows the presence of this disorder.

Today, it is believed that Maria obtained the disease when she was birthed by a
european sailor.


Since it was first recorded by George Huntington, a Long Island doctor,
Huntington’s disease had remained fairly low key. No one heard about it until it
infected Woodie Guthrie, A famous folk singer from the 1920’s who showed
symptoms of the disease. In 1967, he died. This put Huntington’s Disease on the
map, but it still was not well known. But, before Woodie guthrie died, he had a
son, Arlo Guthrie. He, too became a famous folk singer, this time from the
Seventies. He became extremely famous, but had to live with the fact that he has
a 50% chance of having the disorder. That aroused huge public interest and made
the disease well-known.


Now that you know about Huntington’s disease, you can imagine how it works, and
the probability of getting it. But, can you imagine how it feels to have the
disorder? What would it be like to know that you have a 50% chance of not
reaching your sixtieth birthday? Now, enter the life of Nancy Wexler, a woman
who knows how it feels for both of these. She watched as her mother died from
the disease, and has to live with the fact that she may be next. When Wexler was
young, three of her uncles died of the killer disease. “Men only got
Huntington’s disease” went the myth. Then it happened; her sister was told by
her doctor that her unusual walk was an early symptom. She too had the disease.

Since then, she and her sister Alice, swore never to have children. Years later,
Wexler joined up with her husband Milton Wexler, and Marjorie Guthrie, wife of
Woodie Guthrie, and formed the Los Angeles chapter of the Commitee to combat
Huntington’s Disease. Guthrie wanted to focus the organization on patient care,
but Wexler was intent on finding a cure. So, she began to invite biologists to
help study the disease while she worked to get her Ph.D. In 1976 she moved to
Washington to become executive director of the Congressional Commission for the
control of Huntington’s disease and it’s Consequences. Once there, they
discovered that Huntington’s disease works by distroying the Ganglia. Then they
decided that the best way to research Huntington’s disease was at the level of
the gene. They decided to loook for a “marker” (small identifiable piece of DNA)
of where the faulty gene is located. This normally would yave taken 50 to 75
years to find. But, on a freak chance, they found it. it was the 12th marker
that they tested. The discovery of the marker led to the discovery of the gene
which won Wexler the Albert Lasker Public Service Award. The highest honor in
American medicine. She also developed a test to accurately determine whether or
not someone will get Huntington’s disease.


Wexler will not reveal if she, herself has taken the test because she does a
multitude of genetic counciling, and does not want to sway her patients’
decisions on whether or not to take the test. But, whether she tests positive or
negative, Huntington’s disease will live on. Unless scientists like Wexler can
find a cure.

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. (http://www.interlog.com/rlaycock/2nd.html)
REFERENCE PAGE
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
http://www.interlog.com/rlaycock/2nd.html

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