Scientists in the U.S. have announced that for the first time, they have been able to “switch off” the extra chromosome that leads to Down’s syndrome, but this breakthrough comes with some important caveats.
Down’s syndrome (DS) is a congenital disorder that is a result of a person having a third and extra chromosome 21. The condition leads to impaired cognitive ability and physical growth and can result in mild to moderate developmental problems. While a series of tests now offer the possibility of screening for Down’s syndrome early on in pregnancy, no cure is currently available.
However, the prospect of a future therapeutic cure took a step forward this week when researchers from the University of Massachusetts announced they had been able to take cells from volunteers with DS and effectively silence the extra chromosomes present in those samples.
“This will accelerate our understanding of the cellular defects in Down’s syndrome and whether they can be treated with certain drugs,” Jeanne Lawrence, who led the team at the University of Massachusetts, is quoted as saying.
The Massachusetts research team, publishing in the journal Nature, used a procedure known as “genome editing” that allows DNA to effectively be cut and pasted to introduce a gene identified as XIST into the sample cells’ extra chromosomes.
XIST then caused a build up of a particular version of the RNA molecule, coating the chromosome and shutting it down. The cells, and with increasing proficiency, went on to correct for the extra chromosome 21. This research builds on previous findings that have shown the XIST gene’s crucial place in healthy human development.
It is estimated that globally, between one in 1000 and one in 1100 children will be born with DS. While advances in medical treatment mean that DS sufferers now have a longer life expectancy and can expect to reach middle age or beyond, those with DS are at a high risk of heart defects, thyroid problems and a variety of bowel and blood disorders.
While it is true that this research has been characterized as a major technical breakthrough, at this juncture it amounts to very little in terms of its current applications. One thing the research does allow for right now, however, is to enable scientists to begin studying the cellular basis for Down’s syndrome, and this in turn offers the potential of helping to identify particular drug treatments for Down’s syndrome sufferers. It also has wider implications.
There appears no reason to suppose that the XIST gene’s effects should be confined to shutting down the extra chromosome 21. Other developmental abnormalities that are the result of extra chromosomes, like for instance Patau syndrome and its third partial chromosome 13, should in theory also succumb.
The newly announced breakthrough also throws up the exciting prospect of whether in the future we will be able to “turn off” the extra chromosomes that give DS sufferers a significantly higher risk of, for example, leukemia by altering bone marrow cells. A similar process might be used for other conditions such as DS sufferers’ highly elevated risk of developing dementia.
Carol Boys, chief executive of the Down’s Syndrome Association, told the BBC the research is an encouraging breakthrough:
The findings could have serious implications for future work that may be of real benefit to people with Down’s syndrome. We are a very long way from understanding how these findings might translate into clinical applications but it could be that they will be of great assistance in the search for conventional treatments for some of the health conditions that affect people with Down’s syndrome.
However, the prospect of a full chromosome therapy “cure” for DS would mean confronting significant technical and ethical questions.
Put simply, scientists do not yet have the knowledge or the skills needed to be able to fully prevent Down’s syndrome because this would require genome editing on all the prospective child’s cells. Beyond that, the process would require treating an embryo or fetus in the womb. The scope of current law does not allow for such a procedure. It may also draw protest from some religious quarters.
Despite this, the research remains significant and an important breakthrough in unlocking a future where, at the very least, DS sufferers can expect a longer, healthier life.
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