Japanese Scientists Deleted Extra Chromosome Causing Down Syndrome Using CRISPR

Japanese scientists have achieved a breakthrough in genetic research by using CRISPR technology to remove the extra chromosome that causes Down syndrome. This achievement could open new doors for treatments targeting the root genetic cause of the condition, offering hope for millions of families worldwide.

The research team, led by Dr. Ryotaro Hashizume from Mie University, successfully used a method called allele-specific editing to target only the surplus chromosome in lab-grown human cells. Researchers published their findings in PNAS Nexus, and experts have hailed them as a major step forward in gene editing.

“This is the first time we have been able to delete the entire extra chromosome in human cells with such precision,” Dr. Hashizume said. “It gives us a roadmap for future therapies.”

Down syndrome, also known as trisomy 21, occurs when an extra copy of chromosome 21 is present. This genetic condition affects about 1 in every 700 newborns in the United States and leads to a range of developmental, physical, and cognitive challenges. Currently, there are no treatments that address the root cause.

In the study, the researchers designed CRISPR guides that could identify and cut only the extra chromosome copy, leaving the normal chromosomes intact. When they tested this method on stem cells and skin fibroblasts from people with Down syndrome, they were able to remove the extra chromosome in 13 percent of cases. The success rate increased to nearly 30 percent when scientists temporarily turned off DNA repair mechanisms in the cells.

After editing, the treated cells began to behave more like normal cells. Genes linked to nervous system development became more active, while those associated with stress and metabolism showed reduced activity. The corrected cells also grew faster and displayed healthier mitochondrial function.

“This could one day change how we think about genetic disorders,” Dr Hashizume explained. “But we still have a long road ahead before it can be applied in living organisms.

The researchers also tested their method on mature skin cells taken from individuals with Down syndrome. In several cases, they successfully removed the additional chromosome, proving the technique works beyond just stem cells.

Although these results are promising, experts warn that the method is still in its early stages and not ready for use in humans. Delivering gene-editing tools safely to target tissues like the brain remains a major technical challenge. There are also concerns about possible off-target effects, where CRISPR might accidentally alter healthy DNA.

With many advances in gene editing, the breakthrough raises ethical questions. Should scientists try to remove genetic conditions, or should society focus on supporting individuals who live with them?

In Iceland, nearly all women who receive a positive prenatal screening for Down syndrome choose to terminate their pregnancies. This has sparked global debates about how far medicine should go in changing human genetics.

“When we listen to people with Down syndrome and their families, many find the idea of eliminating the condition disturbing,” said Dr. Ástríður Stefánsdóttir, professor of applied ethics at the University of Iceland.

Down syndrome is linked to several health issues. These include congenital heart defects, thyroid problems, and hearing and vision difficulties. It also increases the risk of Alzheimer’s disease with age. Many researchers believe the extra chromosome causes overproduction of certain proteins. This may contribute to these complications.

Japanese scientists removed the surplus chromosome in lab-grown cells. They showed gene expression can normalize. They also found cellular health can improve. However, more studies are needed to confirm safety and effectiveness in real-world use.

“Our goal is not to erase diversity but to provide options for families and individuals,” Dr. Hashizume emphasized. “This is just the first step, but it is a big one.”