Making trisomy 21 a thing of the past

  • People affected by trisomy have three 21 chromosomes rather than two
  • Researchers are now able to neutralize in vitro the extra genes
  • This opens a new venue for new therapies

Researchers have been able to disable trisomy 21 in vitro. Everyone has 23 pairs of chromosomes. People with trisomy 21 (otherwise known as Down’s syndrome), have three copies of chromosome 21 rather than two. This chromosomal anomaly causes a host of different symptoms (cognitive retardation, cardiac deformities etc.) specific to the disorder. The universities of Massachusetts and Vancouver have found how to “neutralize” the extra chromosome.

In order to do this, they sought inspiration from nature, and more specifically from man and woman. There is a particular chromosome that defines, among other things, a person’s sex; XX for female and XY for male. The X chromosome is large and contains 2,000 genes (10% of the genome). A specific gene called the Xist prevents the female from producing twice the protein of the male. It disables one of the X chromosomes by enveloping it in a sort of cocoon. Researchers then thought that it might be possible to do the same with the extra 21 chromosome.

They extracted cells from a person with trisomy 21 and reprogrammed them into stem cells so they could develop into any kind of cell. They then inserted the Xist gene into one of the three chromosomes 21. Within a few days it had woven its cocoon around the chromosome, thus rendering it inactive.

“A giant step”

If gene therapy is in full swing, it’s the first time researchers have been able to act on an entire chromosome. “Numerous studies have already been performed to inhibit specific genes in chromosome 21 such as the DIRYK1A gene which is involved in mental retardation. The results have been inconsistent,” explained Dr. Guy Dembour, pediatric cardiologist and manager of trisomy 21 consultations for Saint-Luc Brussels university clinics.

“The other treatment path is the development of molecules that act on the production of proteins created by the genes. There is EGCG, a green tea extract, that seems to have positive effects on the DYRK1A gene, and by extension on cognitive development. This molecule seems to hold promise without side effects. First, however, clinical studies need to be concluded before integrating it into practice. Until now, studies focused either on the inhibition of a particular gene or on the proteins produced by the chromosome 21 gene. Until recently, I did not think we could act on an entire chromosome. It’s obvious that it would be a giant step forward if we could apply this method in vivo, but first we need to see how we can introduce the Xist gene into a person and also if this method would be 100% effective,” he added.

VIOLAINE JADOUL

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