The study provides the first practical demonstration that chromosomal therapies may become something doable in the future
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To avail themselves of a "genetic tool" inherent in the genome of women, researchers from the United States and Canada were able to turn off the extra copy of chromosome 21, which causes Down syndrome. Research has been done exclusively in a test tube, using cells in culture, and there is no prospect that can produce a "cure" for the syndrome. Still, the study provides the first practical demonstration that chromosomal therapies may become something doable in the future for the treatment of symptoms associated with Down and other syndromes caused by duplication of a chromosome (called trisomies).
"It's a great idea, totally innovative," said geneticist Maria Isabel Melaragno, Federal University of São Paulo (Unifesp), after reading the study, published Wednesday in the journal Nature. The experiment was performed with cells from induced pluripotent stem (iPS) cells derived from a patient with Down syndrome. What the scientists did was to insert the extra chromosome cells copy of a gene called XIST, normally responsible for "mute" (or off) one copy of the X chromosome in women.
The effect is the same: the disabled XIST genes extra chromosome 21, causing the cells functioned as genetically normal units. "What they did, essentially, was to insert a 'switch' gene which allows you to turn off the entire chromosome," said researcher Lygia Pereira, University of São Paulo. (USP). "It's a neat trick. They took this natural tool for silencing of chromosome X and used to silence another chromosome. "
Although women have two x chromosomes, only one is 100% functional. The other is almost completely silenced by XIST early embryonic development, to avoid "overdose" of proteins in the body. The muting is accomplished by means of biochemical called "epigenetic" which do not alter the DNA sequence of the genes but install "latches" and cause structural modifications which inhibit or alter the operation. RNA molecules encoded by chromosome XIST overlying as a cover - or in this case a clamp.
The research was led by Dr. Jeanne Lawrence, Faculty of Medicine, University of Massachusetts, in the United States. The study was submitted to Nature for publication in May 2012 but was not formally accepted by the magazine in June, after more than a year of review, which gives an idea of the complexity of the project.
APPLICATIONS - The implication more "futuristic" work, according to the authors, is put Down syndrome in the list of diseases that may benefit from gene therapy - or chromosome - in the future. At no time, however, they speak of "cure" or reverse the syndrome.
"The effects of trisomy 21 in Down syndrome has occurred since the beginning of embryonic development, there is no getting around that," says Maria Isabel, Unifesp. According to her, however, it is feasible to think of therapies to alleviate some of the adverse effects of the syndrome, such as hematological and neurological diseases that often affect patients.
No studies in animal models, there is no way to predict what would be the effect of silencing chromosome into a living organism. In cells in which the extra chromosome was silenced in artificial medium, but there was a reduction in the deficit of neuronal cells proliferation, which is one of the difficulties associated with Down's syndrome.
Source: State Agency
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