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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.
Huntington's disease is caused by a mutation in the HD gene in which the same three bases? (CAG) are repeated many more times than normal. This is known as a CAG trinucleotide repeat expansion. In people who don't have Huntington's disease this section of CAG repeats in the gene is usually only repeated 10 to 35 times.
Huntington's disease is caused by a faulty gene. Cells in parts of the brain are very sensitive to the effects of the faulty gene. This makes them function poorly and eventually die. A parent with the Huntington's disease gene has one good copy of the gene and one faulty copy.
While Huntington's Disease is caused by a toxic gain of function due to polyQ expansion, multiple models suggest that a loss-of-function of the wildtype Htt protein may contribute significantly to several components of disease pathology (as summarized in Figure 2).
Huntington's disease is a progressive brain disorder caused by a single defective gene on chromosome 4 — one of the 23 human chromosomes that carry a person's entire genetic code. This defect is "dominant," meaning that anyone who inherits it from a parent with Huntington's will eventually develop the disease.
Examples of gain of function mutations include mutations that prevent clearance of protein from the cell surface via endocytosis due to mutation of the required recognition sequence, mutations that result in constitutive activation of a receptor, and mutations in regulatory sites that lead to a protein's constitutive ...
Although anyone can develop HD, it tends to run in people of European descent (having family members who came from Europe). But the main factor is whether you have a parent with HD. If you do, you have a 50% chance of also having the disease.
Point and chromosomal mutations have been identified as the cause of many human diseases. With regard to HD, however, they do not appear to play a role. Instead, the mutation involved in HD is known as an expansion.
Huntington's disease is characterized by a loss of brain striatal neurons that occurs as a consequence of an expansion of a CAG repeat in the huntingtin protein. The resulting extended polyglutamine stretch confers a deleterious gain-of-function to the protein.
Deletion. Deletion mutations are actually the cause for a large number of genetic diseases, such as two-thirds of cystic fibrosis cases and the cat cry syndrome, which is so-called because children with this syndrome often have a cry that sounds similar to a cat meowing.
Types of Mutations
There are three types of DNA Mutations: base substitutions, deletions and insertions.
The disease results from changes (mutations) of a gene known as “huntington” located on the short arm (p) of chromosome 4 (4p16. 3). In those with the disorder, the huntington gene contains errors in the coded “building blocks” (nucleotide bases) that make up the gene's instructions.
The range of disease duration was between 2 and 17 years, the oldest living to age 91.
On average, individuals with Huntington's disease live for 10 to 30 years after the onset of symptoms. However, it is essential to note that this is an average estimate, and some individuals may live longer or shorter than this range.
While the cause of the disease is known — a single mutated gene — there is no cure. “Our plan is to conduct human clinical trials that deliver stem cells to replace damaged brain cells, reducing levels of harmful proteins that build up in the brains of Huntington's disease patients.”
In the United States, Huntington's disease occurs in about one of every 10,000 to 20,000 people. It affects males and females equally and crosses all ethnic and racial boundaries. Typically, symptoms begin between age 30 and 55.
Prevention of Huntington's disease
Because Huntington's is a genetic disease, you can't do anything to prevent it if you have inherited it. If you have a history of Huntington's disease in your family, you may wish to have genetic counseling before having children of your own.
Huntington's is a dominant genetic disease. With these diseases, you are almost never an invisible carrier like you can be with recessive genetic diseases. You usually can't pass on a gene that causes the disease because you don't have it.
A lethal mutation is a type of mutation in which the effect(s) can result in death or reduce significantly the expected longevity of an organism carrying the mutation. For instance, brachydactyly is fatal when the genetic defect is expressed during infancy in homozygous recessive individuals.
Mutations can result from errors in DNA replication during cell division, exposure to mutagens or a viral infection.
Two major categories of mutations are germline mutations and somatic mutations.
Since the Huntington gene is not on a sex-determining chromosome, the disease is not sex-linked. In other words, the inheritance and development of Huntington's disease are not related to an individual's sex. This means that males and females have an equal chance of inheriting the disease.