A Nature study published online Wednesday described how a US team used a naturally occurring genetic technique to silence the extra chromosome responsible for Down syndrome, also known as trisomy 21. Trisomy 21 causes learning difficulties, and many physical health disadvantages, including heart defects, greater risk for childhood leukemia, disrupted immune and endocrine systems, and early development of Alzheimer’s disease.
Scientists have shown for the first time in a lab setting that it’s possible to “silence” the extra chromosome responsible for Down syndrome. Jeanne Lawrence, a cell biologist at the University of Massachusetts said in a statement that the last ten years have seen huge progress in ability to correct single-gene disorders. These projects started with test tube cells, moved to live cells, and now some are at the clinical trial stage.
“By contrast, genetic correction of hundreds of genes across an entire extra chromosome has remained outside the realm of possibility. Stem-cell researcher Nissim Benvenisty of Hebrew University in Jerusalem says in a Nature News report on the study that for researchers working on Down syndrome, “the idea of shutting off a whole chromosome is extremely interesting.”
Lawrence and her team devised an approach to mimic the natural process that silences one of the two X chromosomes carried by all female mammals. Both chromosomes contain a gene called XIST (the X-inactivation gene), which, when activated, produces an RNA molecule that coats the surface of a chromosome like a blanket, blocking other genes from being expressed. In female mammals, one copy of the XIST gene is activated — silencing the X chromosome on which it resides.
She anticipates future studies will compare cells with chromosome 21 switched on to cells with it switched off, in order to see how they differ in function and response to treatment.
Transcript to Here and Now NPR program on this topic.
Progress is being made. Though it may be years before human applications is viable there is glistening hope on the horizon for genetic therapy not only for Down Syndrome but for other conditions such as blood disorders and cancer.