Human trisomy 21, which is responsible for Down syndrome, is the most prevalent chromosomal abnormality responsible for cognitive impairment and a key focus of prenatal and preimplantation diagnosis. The presence of an extra chromosome 21 is the root problem, and few researcher have tried to directly eradicate it. However, a novel study demonstrates the successful removal of the extra chromosome 21 from human cells using CRISPR-Cas9 gene-editing technology (molecular scissors that allow scientists to make precise changes to DNA, like cutting, removing, or replacing specific genes).
The researchers developed a highly precise allele-specific (AS) CRISPR-Cas9 strategy which is capable of identifying and removing this third extra chromosome without damaging the two necessary ones. This was accomplished by creating a comprehensive method to extract AS Cas9 target sequences.
The scientists did this experiments on human cells that had Down syndrome. These included special cells called induced pluripotent stem cells and fibroblasts (a type of skin cell). They were able to eliminate the extra chromosome 21 in more than 30% of the cells using CRISPR-Cas9.
When they temporarily turned off certain genes that usually repair DNA damage—like TP53—they made the process even more effective, removing the extra chromosome untill 37.5% of the cell. Which not only remove the extra chromosome but also correct abnormal gene activity.
However, the method is not yet ready for human or animal trials. Further research is needed to ensure the long-term safety and stability of such gene-editing procedure. However, gene therapy is entering a new era when illnesses that were previously believed to be permanent could eventually be fixed at the genetic level. Before gene editing can be used in medical treatments, especially in embryos, scientists must carefully think about the ethical issues .
