Japanese researchers at Mie University achieved a pioneering feat by using CRISPR-Cas9 to selectively remove the extra chromosome 21 responsible for Down syndrome in cultured human cells. This first-ever complete elimination of a trisomic chromosome restored more typical gene expression patterns and cell behaviors, including normalized proliferation and reduced inflammatory gene activity. While this proof-of-concept marks a breakthrough in gene editing applications for chromosomal disorders, it raises ethical considerations regarding future therapeutic potentials and human applications.