Science has managed to switch off the extra chromosome in Down syndrome. It has also opened the major ethical debate over gene editing

Beth Israel Deaconess Medical Center researchers reported a modified CRISPR/Cas9 method that improved insertion of XIST into trisomy 21 cells.

The approach silenced the extra chromosome 21 in a subset of tested cell lines, with XIST integration rates of about 20% to 40%.

The work builds on earlier proof-of-concept studies and suggests a possible path toward treating Down syndrome at its genetic root.

But the technique is still far from human use because of off-target effects, mosaicism, and incomplete editing, alongside major ethical concerns.