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CRISPR modification improves the efficiency of EGFP integration into the APP gene locus of HEK293 cells. Credit: Proceedings of the National Academy of Sciences (2026). DOI: 10.1073/pnas.2517953123
Scientists have taken an important step toward a gene therapy that could one day turn off the extra genetic material that causes Down syndrome (DS). Down syndrome is a genetic condition caused by an extra chromosome 21 (and consequently hundreds of triplicate genes) that leads to developmental and neurological issues. According to the Washington-based National Down Syndrome Society, approximately 1 in every 640 babies in the United States is born with DS. That makes it the most common chromosomal condition.
Traditional gene therapy targets one or two genes, but in this approach, scientists at Beth Israel Deaconess Medical Center and Harvard Medical School found a way to silence much of the extra chromosome's activity in the cell at once.
Details of their research are published in a paper in the journal Proceedings of the National Academy of Sciences.
A new way to use a gene-editing tool
In normal development, every biological female has two X chromosomes in most cells. To prevent a double dose of genetic instructions, a gene called XIST naturally shuts down one of the chromosomes.
The team used a modified version of the gene-editing technique CRISPR/Cas9 (often used like molecular scissors to cut or edit DNA sequences) to insert the XIST gene into the extra chromosome 21 to silence it.
They tested their technique in the lab using human stem cells that contained an extra chromosome 21. After running several experiments, the team found that CRISPR was effective at pasting the XIST silencing gene exactly where it needed to go. As they noted in their paper: "Our modified CRISPR method significantly enhanced the integration efficiency (20 to 40%) of the long XIST gene (14 kb) into an extra chromosome 21."
Future steps
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