Trinucleotide repeat expansion


Trinucleotide repeat expansion

=Trinucleotide repeat expansion=

Trinucleotide repeat expansion, also known as triplet repeat expansion, is the DNA mutation responsible for causing any type of disorder categorized as a trinucleotide repeat disorder. These are labelled in dynamical genetics as dynamic mutations.cite journal |author=Richards RI, Sutherland GR |title=Dynamic mutation: possible mechanisms and significance in human disease |journal=Trends Biochem. Sci. |volume=22 |issue=11 |pages=432–6 |year=1997 |pmid=9397685 |doi=]

Triplet expansion is caused by "slippage" during DNA replication. Due to the repetitive nature of the DNA sequence in these regions, 'loop out' structures may form during DNA replication while maintaining complementary base paring between the parent strand and daughter strand being synthesized. If the loop out structure is formed from sequence on the daughter strand this will result in an increase in the number of repeats. However if the loop out structure is formed on the parent strand a decrease in the number of repeats occurs. It appears that expansion of these repeats is more common than reduction. Generally the larger the expansion the more likely they are to cause disease or increase the severity of disease. This property results in the characteristic of anticipation seen in trinucleotide repeat disorders. Anticipation describes the tendency of age of onset to decrease and severity of symptoms to increase through successive generations of an affected family due to the expansion of these repeats.

In 2007 a new disease model was produced to explain the progression of Huntington's Disease and similar trinucleotide repeat disorders, which, in simulations, seems to accurately predict age of onset and the way the disease will progress in an individual, based on the number of repeats of a genetic mutation. [News Release, Weizmann Institute of Science, "Scientists at the Weizmann Institute, using computer simulations, have provided an explanation as to why certain genetic diseases caused by repeats in the code are “genetic time-bombs” whose onset and progression can be accurately predicted," November 21, 2007, at http://80.70.129.162/site/en/weizman.asp?pi=371&doc_id=5042. Retrieved on 2007-12-30. ]


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