CRISPR deleted the extra chromosome behind Down syndrome. In a groundbreaking world-first, researchers have successfully used CRISPR gene-editing technology to remove the extra chromosome responsible for Down syndrome, opening a potential path toward treating genetic disorders previously considered incurable. Down syndrome, or trisomy 21, occurs when a person has three copies of chromosome 21 instead of the usual two. It is one of the most common genetic conditions, affecting about 1 in 700 babies worldwide, and leads to intellectual disability, developmental delays, and various health issues. Until now, no treatment has been able to correct the underlying cause. That may soon change. In a new proof-of-concept study, scientists applied CRISPR-Cas9 to cells taken from people with Down syndrome—including skin cells and pluripotent stem cells—and successfully eliminated the extra chromosome 21. The edited cells showed a striking return to normal gene expression patterns and cellular function. To improve precision, the team briefly disabled certain DNA-repair pathways during the process, making the chromosome removal cleaner and more effective. At this stage, the technique has only been demonstrated in laboratory cell cultures and is far from ready for human use. Removing an entire chromosome carries significant risks, including possible off-target effects, so extensive safety work lies ahead. If those challenges can be overcome, however, the approach could one day be applied to brain cells or even used during early fetal development. The implications extend beyond Down syndrome. The same strategy might eventually treat other life-limiting trisomies, such as trisomy 13 and trisomy 18, which are often fatal in infancy or cause severe disability. For the first time, a tool exists that could, in principle, correct the root chromosomal abnormality rather than merely managing symptoms. ["Trisomic rescue via allele-specific multiple chromosome cleavage using CRISPR-Cas9 in trisomy 21 cells." PNAS Nexus, 2025]