Study claims to silence Downs syndrome gene

In what is being described as a major breakthrough in the management of genetic disorders attributed to tripling of chromosome pairs,scientists have managed to silence or switch off the entire extra chromosome in cells taken from a Downs syndrome patient in laboratory. This silencing of trisomy,as it is medically termed,can play an important role in future research into finding a cure for diseases attributed to similar genetic defects.

Downs syndrome is caused by a trisomy or tripling of the 21st chromosome,which leads to genetic problems. A team of doctors from the University of Massachusetts imported a single gene from a normal X chromosome into a specific location on the extra 21st chromosome. This gene,XIST,is an X inactivation gene responsible for turning off the effects of one of the X chromosomes in women. Women are born with a pair of X chromosomes and naturally turn off the effects of cells associated with one of the X chromosomes. The team of genetic experts,led by Dr Jeanne Lawrence,has written in Nature: We set out to determine whether the human X inactivation gene,XIST,could be inserted into one copy of chromosome 21,and enact a chromosome wide change in its epigenetic state. This,Lawrence adds,would provide a system to study Downs syndrome cell pathology,and be a possible first step towards a potential genetic approach to chromosome therapy.

Explains Dr Suresh Seshadri,a foetal geneticist based in Chennai,This is a wonderful new concept since it is taking a leap forward from therapy targeted towards single genes to one that seeks to impact the entire chromosome with thousands of genes,all at once. Seshadri,however,cautioned that this concept has only been achieved on a laboratory bench,and it may take years for it to translate into humans.

Critics say that it may take years to achieve these results in animals,let alone humans. The Downs Syndrome Federation of India has given the study a lukewarm response. Dr Rekha Ramachandran,president of the federation,said,This seems like a far fetched idea at best,and will take years to reap benefits for patients.