Scientists at Mie University in Japan have successfully utilized CRISPR-Cas9 to remove the extra chromosome 21 responsible for Down syndrome in cultured human cells. This allele-specific gene editing strategy selectively targets and eliminates the trisomy without affecting normal chromosomes, resulting in cells with more typical behavior and gene expression profiles. The edited cells demonstrated increased growth rates and normalized activity of genes linked to brain development and metabolism. This landmark application of CRISPR for whole chromosome deletion opens new avenues for future therapies, though ethical discussions remain ongoing.