Researchers have developed a modified version of the CRISPR gene-editing tool that in early laboratory experiments suggests it may have the potential to “silence” the extra chromosome that causes Down syndrome.

People with Down syndrome are born with an extra copy of chromosome 21, giving them 47 chromosomes instead of the usual 46.

“Because of this extra copy, many genes are disrupted and contribute to the cognitive impairment and early-onset Alzheimer's disease” associated with the condition, said study leader Dr. Volney Sheen of Beth Israel Deaconess Medical Center in Boston.

As it is not ‌clear which of the hundreds of genes on the extra chromosome are to blame for these effects, silencing of the entire chromosome would be ​the optimal treatment, Sheen said.

In healthy biological females, a gene called XIST naturally silences the extra X chromosome that is present in all female cells except eggs. Scientists have previously surmised that inserting XIST into an extra chromosome 21 will silence it in a similar manner, ⁠but technical limitations meant their attempts at inserting the gene often failed.

Among the challenges was that XIST must be inserted into only one of a cell's ​three copies of chromosome 21, and this needs to happen in as many cells as possible, Sheen noted. His team's modified CRISPR improved integration of the XIST ⁠gene into the extra chromosome by roughly 30-fold over the conventional CRISPR approach, according to a report in PNAS.

Although the technique is still at the test-tube stage, the researchers hope it will lead to future treatments.

While the strategy of chromosome-wide silencing for Down syndrome “is highly promising” and the researchers’ improved efficiency at inserting the XIST gene is “generally quite significant,” the new results represent only proof-of-concept research at the cellular ‌level, said Dr. Ryotaro Hashizume of Mie University Hospital in Japan, who was not involved in the research.