Early-stage research could eventually lead to gene therapy

By Tina Hesman Saey

Web edition: July 17, 2013

Borrowing a trick from nature, researchers have switched off the extra chromosome that causes Down syndrome in cells taken from patients with the condition.

Though not a cure, the technique, reported July 17 in Nature, has already produced insights into the disorder. In the long run it might even make the flaw that causes Down syndrome correctible through gene therapy.

Gene therapy is now on the horizon, says Elizabeth Fisher, a molecular geneticist at University College London. But that horizon is very far away.

Down syndrome, also called trisomy 21, occurs when people inherit three copies of chromosome 21 instead of the usual two. It is the most common chromosomal condition, affecting around one in every 700 babies born in the United States. People with the disorder typically have both physical and cognitive complications of having an extra chromosome.

Down syndrome has been one of those disorders where people say, Oh, theres nothing you can do about it, says Jeanne Lawrence, a chromosome biologist and genetic counselor at the University of Massachusetts Medical School in Worcester, who led the study with colleague Lisa Hall.

The researchers decided to see whether they could shut down the extra chromosome by drawing on a biological process called X inactivation. Women have two X chromosomes and men have only one X and a Y. To halve the amount of X chromosome products, female cells shut down one copy. Cells do that using a chunk of RNA called XIST, which is made by one X chromosome but not the other. The RNA works by pulling in proteins that essentially board up the chromosome like an abandoned building. The other X stays on by making a different RNA.

Lawrence and Hall thought that if they put XIST on another chromosome, it might shut that one down too. So the researchers put the gene for XIST onto one of the three copies of chromosome 21 carried by stem cells grown from a man with Down syndrome. That copy of the chromosome got switched off.

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Technique inactivates Down-causing chromosome

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