3/21 the day for Trisomy 21

Prenatal screening, children with unique characteristics, anxious parents, and a life different from the usual. What is Down syndrome, and why is today dedicated to raising awareness about it?

March 21st (3/21) has been designated since 2006 as World Down Syndrome Day, with the date symbolizing the triplication of the 21st chromosome. Thanks to an initiative by Greek physician Stylianos Antonarakis, a Professor of Genetics at the University of Geneva, we now have a special day each year for our fellow humans, with what is commonly known as Down syndrome—people who, despite genetic challenges, fight daily battles, overcome obstacles, and achieve new milestones in a world that, until recently, marginalized them.

Down syndrome, also known as Trisomy 21, was first described in 1866 by Dr. John Langdon Down, who linked a series of characteristics affecting the musculoskeletal, cardiovascular, and nervous systems. In 1959, the syndrome was connected to the presence of an extra chromosome in affected individuals, specifically an additional copy of chromosome 21. Today, the birth rate of children with Down syndrome has doubled compared to 1950—from 3.3 per 10,000 individuals to 6.7 per 10,000, according to population studies in the United States, while in Europe, the rate stands at 5.7 per 10,000. Adding to that, life expectancy has increased from 26 years to 58, all thanks to advancements in modern medicine.

One of the contributing factors to the occurrence of Trisomy 21 in embryos is the increased maternal age—a trend that has become more common as the age of first-time pregnancy has risen in recent years.

Couples who wish to have a child without Down syndrome can undergo prenatal screening (NIPT) as early as the 9th week of pregnancy or detect the condition later through an ultrasound at the 11th week. However, even if they decide to continue the pregnancy, individuals with Down syndrome fortunately have a much better life expectancy today than in the past.

Just last month (February 2025), a team of researchers from Japan delivered an optimistic breakthrough, as they successfully removed the extra chromosome in cell culture studies. Using the molecular “scissors” of the CRISPR/Cas9 enzyme system, Hiroki Kurahashi and his colleagues achieved the removal of the extra chromosome 21 through targeted gene editing.

Essentially, using embryonic-like stem cells engineered to contain the extra chromosome, the researchers were able to intervene and convert them into healthy cells. But they didn’t stop there—they also worked with differentiated cells, such as fibroblasts, and successfully removed the extra chromosome from them as well.

What could this mean if the technique advances significantly? It suggests that if a woman carrying a fetus with Down syndrome undergoes prenatal screening, she might one day be able to intervene and remove the problematic extra chromosome to deliver a healthy child. Furthermore, individuals already born with Down syndrome could potentially benefit from improved tissue function, making associated medical conditions more manageable.

However, several challenges must be overcome before such a specialized treatment can become established and reach clinical practice. Beyond the fact that this study was conducted under highly controlled laboratory conditions, CRISPR/Cas9 technology has a margin of error. The enzymes might cut in the wrong location, leading to unintended mutations in other parts of the genome or even in other chromosomes, with potentially serious consequences.

Even if this issue is eventually resolved and the error rate is significantly reduced, extensive studies in model organisms will be needed before the technique can be applied to humans. The complexity of an entire organism is vastly different from the controlled environment of cultured cells.

Nevertheless, we hold onto the hopeful message that, in the future, this challenging condition may become treatable.

In conclusion, beyond the medical aspect, as a society, we can stand up for the rights of our fellow humans with Down syndrome whenever and wherever possible, making their daily lives more beautiful and our world more inclusive and functional—guided by love and inclusivity.

*Note: The cells used in the study were not derived from embryos but were model cells that mimic embryonic cells.

Sources: [1] de Graaf, G., Buckley, F., Skotko, B. People living with Down syndrome in the USA: births and population. Down Syndrome Education International (2019), [2] Correction to: Estimation of the number of people with Down syndrome in Europe | European Journal of Human Genetics , [3] Ryotaro Hashizume et al., Trisomic rescue via allele-specific multiple chromosome cleavage using CRISPR-Cas9 in trisomy 21 cells, PNAS Nexus, Volume 4, Issue 2, February 2025