is a genetic disorder caused by the presence of all or part of a third copy of chromosome 21 (that occurs when people inherit three copies of chromosome 21 instead of the usual two). A chromosome
is a single piece of coiled DNA containing many genes; the chromosome encodes most of a person’s genetic information.
The condition is typically associated with physical growth delays, a particular set of facial characteristics and a severe degree of intellectual disability. The condition affects one in every 700 babies born in the United States.
For this new study, researchers attempted shut down the extra chromosome by drawing on a biological process called X inactivation (or "genome editing", a procedure that allows DNA to be cut and pasted), according to The Guardian
. 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.
To demonstrate this, the scientists
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 was successfully switched off.
The study advances thinking about the molecular basis of the genetic disorder. The researchers next plan to carry out animal experiments. The long-term aim is for a human trial using gene therapy.
The study was led by Jeanne Lawrence, a chromosome biologist and genetic counselor at the University of Massachusetts Medical School in Worcester. The research findings have been published
in Nature in a paper titled “Translating dosage compensation to trisomy 21.”