Down syndrome is caused by genetic disorder when in DNA chromosome #21 has three copies (instead of 2 copies). If I understand correctly then the Genetic Engineering is the closest field in modern medicine that studies how to alter host's DNA.
Would there in next few years be a cure for Down's syndrome (i.e. remove the third copy of chromosome #21 in an adult's DNA)? If not, then what are difficulties that would still need to be overcome in genetic engineering to do something like that?
For example, is it impossible to consistently change DNA for all cells in body? Would these cells start to "attack" each other while being in partially reconfigured state?). If I understand correctly then CRISPR* method is the new tool in genetic engineering that may allow to do such DNA manipulations?
P.S. as it may be obvious from my question I don't have medical background and my questions is motivated by having relative affected by Down's syndrome.
P.P.S. I found this link http://www.prnewswire.com/news-releases/new-down-syndrome-therapy-discovered-300135102.html - not sure how to interpret it.