🚨 Scientists Successfully Remove an Extra Chromosome 21 From Human Cells Scientists in Japan have demonstrated a remarkable new approach for dealing with the genetic cause of Down syndrome. Using the gene-editing tool CRISPR-Cas9, researchers were able to selectively remove an extra copy of chromosome 21 from human cells carrying trisomy 21. Most human cells contain two copies of chromosome 21. In Down syndrome, there are three. Unlike conditions caused by a single DNA mutation, trisomy 21 involves an entire extra chromosome, making it much more difficult to correct. The researchers designed CRISPR guides that could recognize genetic differences unique to one copy of chromosome 21. The system then repeatedly targeted that chromosome, eventually causing some cells to lose the extra copy. In induced pluripotent stem cells, the researchers were able to restore some cells from three copies of chromosome 21 to the usual two. Under certain experimental conditions, the chromosome-removal efficiency reached 37.5%. The changes were not limited to chromosome number. Cells that lost the extra chromosome also showed changes in gene activity, growth patterns and antioxidant activity, moving closer to the patterns seen in cells with two copies of chromosome 21. The researchers also demonstrated that the technique could work in fibroblasts and in cells that were not actively dividing, suggesting that the approach may not be limited to rapidly growing cells. This is significant because scientists are not simply correcting one faulty gene. They are exploring whether an entire unwanted chromosome can be selectively removed from a human cell. However, this remains laboratory research and is not a treatment for people with Down syndrome. Major challenges remain, including safely delivering CRISPR machinery to the right cells throughout the body, avoiding unintended genetic changes and determining which tissues could benefit from chromosome removal. For now, the study provides an important proof of principle: researchers have demonstrated a targeted method that can remove an extra chromosome 21 from human trisomy 21 cells and partially reverse some of the associated cellular changes. Source: Mie University; PNAS Nexus