In a pioneering step towards treating the genetic root of Down syndrome, researchers in Japan have successfully corrected trisomy 21 cells using precision CRISPR-Cas9 gene editing that targets and removes the extra chromosome without affecting the healthy ones.
Published in the PNAS Nexus, the study introduces an allele-specific chromosome elimination strategy—a method that precisely identifies and slices only one of the three copies of chromosome 21 in trisomy cells. This breakthrough lays the groundwork for future genetic therapies aimed at correcting aneuploidies at their source.
CRISPR Meets Chromosomal Surgery
Down syndrome, the most common chromosomal disorder, is caused by an extra copy of chromosome 21. Current approaches only manage symptoms. This new study changes the game by targeting the extra chromosome directly.
Using CRISPR-Cas9, the team engineered guide RNAs that only recognized specific sequences on the extra maternal chromosome. Unlike previous methods that risked damaging healthy DNA, this allele-specific (AS) approach ensured selective editing. With multiple targeted cuts, the cell naturally discarded the damaged chromosome—a process known as trisomic rescue.
“This is the first time we’ve shown that trisomy 21 can be corrected at the cellular level using allele-specific CRISPR,” said lead author Dr. Ryotaro Hashizume of Mie University, Japan.
From Trisomy to Disomy: Real Correction, Real Results
Experiments using induced pluripotent stem cells (iPSCs) and skin fibroblasts derived from a child with Down syndrome showed up to 30.6% correction efficiency using 13 targeted DNA cuts. The corrected cells reverted from trisomy (three chromosomes) to disomy (two chromosomes), restoring normal karyotypes.
The results were confirmed using fluorescence in situ hybridization (FISH), STR profiling, and G-banding karyotyping—standard tools in genetic cytogenetics.
Genetic Reboot: Gene Expression Normalized
Beyond correcting chromosome count, the team demonstrated that trisomy correction also reversed the abnormal gene expression profile associated with Down syndrome. Gene sets related to neurogenesis and central nervous system development were reactivated, while metabolic stress pathways were reduced.
This suggests that removing the extra chromosome not only fixes DNA quantity but also resets cellular function, potentially correcting many downstream effects of the disorder.
Safer, Smarter Editing with Allele-Specific Targeting
The study compared allele-specific (AS) with traditional allele-nonspecific (ANS) CRISPR strategies. AS targeting proved:
- More efficient in eliminating the extra chromosome.
- Less harmful to healthy chromosomes.
- More precise, avoiding dangerous off-target effects.
Additionally, suppressing DNA repair genes like POLQ and LIG4 temporarily boosted chromosome elimination rates, hinting at a path to even more effective interventions.
Can This Become a Therapy?
Although this is still early-stage lab research, the implications are massive. Trisomy correction in nondividing cells was also successful, meaning this could potentially be applied to brain or heart tissue in the future, two organs heavily affected in Down syndrome.
The research team is cautious, however. “We need more studies on delivery, long-term safety, and efficacy in vivo,” Dr. Hashizume noted. But the proof-of-concept is compelling: it may soon be possible to edit out the genetic cause of Down syndrome.
What’s Next?
Future studies aim to:
- Develop delivery methods for in vivo treatment (e.g., viral or nanoparticle vectors).
- Test the therapy in animal models and organoids.
- Eliminate the need for DNA cuts entirely by switching to epigenetic silencing or dead-Cas9 methods.
TL;DR:
Japanese scientists have used CRISPR-Cas9 to precisely remove the extra chromosome in Down syndrome cells by targeting only the redundant copy, achieving trisomic rescue. This could open a future path to actual cures for chromosomal disorders, not just symptom relief.
Reference
Hashizume, R., Wakita, S., Sawada, H., Takebayashi, S. I., Kitabatake, Y., Miyagawa, Y., … & Kurahashi, H. (2025). Trisomic rescue via allele-specific multiple chromosome cleavage using CRISPR-Cas9 in trisomy 21 cells. PNAS nexus, 4(2), pgaf022. https://doi.org/10.1093/pnasnexus/pgaf022
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