- 11:00
Japanese researchers have succeeded in removing, in the lab, the extra chromosome responsible for Down syndrome using CRISPR-Cas9 technology. A world first that opens unprecedented perspectives; yet remains, for now, an experimental advance full of challenges.
It is a milestone in the history of Down syndrome research. A team from Mie University in Japan has shown that it is possible, through CRISPR-Cas9 gene editing, to erase the supernumerary chromosome that causes the condition, at least in cells grown in labs. The announcement, published in the scientific journal PNAS Nexus, made headlines, as it targets the very root of the disease: the presence of a third copy of chromosome 21 instead of the usual two.
The Japanese team used CRISPR-Cas9 to specifically target this third chromosome in various cell types from patients with Down syndrome: pluripotent stem cells (which can give rise to various tissues) and fibroblasts, i.e. mature skin cells. The approach: “break” the DNA of the extra chromosome so that the cell would eliminate it during division.
In order to achieve this, they had to refine their method and combine CRISPR with other techniques, such as the temporary inhibition of genes involved in DNA repair, to boost the likelihood that the cell would actually discard the targeted chromosome.
Results are striking: under the best conditions, about 37.5% of treated cells lost the extra chromosome and became “disomic” again, with only two chromosome 21s, just like in a non-trisomic individual. These “corrected” cells then displayed characteristics closer to normal, whether in growth, gene expression, or resistance to oxidative stress.
Limits and Major Challenges
Despite its promise, the breakthrough raises major questions and limitations. First, the experiment took place exclusively in vitro, i.e. in petri dishes, on isolated cells. It is still far from being applicable to a whole organism, whether in animals or humans.
Second, while the deletion rate is unprecedented, it remains incomplete: more than 60% of treated cells retained their extra chromosome. For any therapeutic application, far higher efficiency will be needed, along with guarantees against serious side effects such as accidentally deleting other essential genes.
Other crucial issues remain: the long-term stability of the changes, the ability to target cells across various organs (brain, heart, etc.), or the possibility of correcting trisomy at a very early stage of embryonic development, before the most severe symptoms appear.
Finally, the breakthrough raises ethical questions: how far should humanity go in editing the human genome? Should genome editing be considered in embryos, or only after birth? And what are the long-term consequences, for individuals and for society?
Such questions are ones that science must address as it moves forward with its research.
A Key Step, Yet Still Experimental
The Japanese study marks a major scientific breakthrough in understanding and manipulating Down syndrome. It proves that it is theoretically possible to target and remove an entire chromosome in human cells using CRISPR. Such a feat, unthinkable only a few years ago, opens new avenues for genetic research, well beyond Down syndrome.
Yet the road to clinical application is long. Trials must demonstrate the feasibility, efficiency, and safety of such an approach in whole organisms, without side effects or genetic drift. The technical, biological, and ethical hurdles are immense. Still, the Japanese achievement gives new momentum to research and fuels hopes for future treatments that could tackle the very root of chromosomal diseases.
For now, the breakthrough is a reminder of the power of modern gene editing and the need to advance with caution and responsibility. The story of Down syndrome may be entering a new era, but the journey is only beginning.
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