Using CRISPR to remove extra chromosomes in Down syndrome

Researchers at the University of Tokyo removed the extra chromosome from trisomy 21 (Down syndrome) human cell lines, restoring normal gene expression.

From PNAS Nexus 25/02/25 (first released 18/02/25)

Gene editing techniques may eventually allow trisomy to be treated at the cellular level, according to an in vitro proof-of-concept study.

Down syndrome is caused by the presence of a third copy of the 21st chromosome.

The condition occurs in approximately 1 in 700 live births and is relatively easy to diagnose at early stages of development.

However, there are no treatments.

Ryotaro Hashizume and colleagues use the CRISPR-Cas9 gene editing system to cleave the third chromosome in previously generated trisomy 21 cell lines derived from both pluripotent cells and skin fibroblasts.

The technique is able to identify which chromosome has been duplicated, which is necessary to ensure the cell does not end up with two identical copies after removal, but instead has one from each parent.

The authors were able to remove duplicate chromosomes from both induced pluripotent stem cells and fibroblasts.

Suppressing chromosomal DNA repair ability increased the rate of duplicate chromosome elimination.

The authors show that the chromosomal rescue reversibly restores both gene expression and cellular phenotypes.

The approach is not yet ready for in vivo application, however, in part because the current technique can also change the retained chromosomes.

According to the authors, similar approaches could eventually be used in neurons and glial cells and form the basis of novel medical interventions for people with Down syndrome.