A rare medical case involving identical twin brothers — one born with Down syndrome and the other without — is offering researchers an unprecedented opportunity to advance the scientific understanding of the genetic roots and biological impact of trisomy 21.
According to a statement emailed to Zeale News, doctors at the Catholic-founded Jerome Lejeune Institute identified the case in 2018 after the birth of Christian and Gabriel. The boys are monozygotic twins, meaning they developed from the same fertilized egg and share nearly identical DNA. Yet one brother carries an extra copy of chromosome 21 — the genetic condition that causes Down syndrome — while the other does not.
The discovery prompted the creation of the COLIBRI research project in 2022, an initiative funded by the Institute’s parent organization the Jerome Lejeune Foundation and launched through BRC-BioJel, the foundation’s biological resource center. The project aims to advance medical research and care for individuals with genetic intellectual disabilities. Researchers said the project’s name, “COLIBRI,” French for “hummingbird,” carries special symbolic meaning.
Hummingbirds “are the smallest birds in the world, and they can fly backward. No other bird does that!” Marie Vilaire, head of the BRC, explained in the statement. “These tiny boys also had very special characteristics.”
Because the twins share the same genetic background, physicians say they can isolate the specific effects of trisomy 21 with unusual precision, without the confounding variables that typically complicate studies comparing unrelated individuals. The project combines ongoing clinical monitoring with laboratory analysis, including epigenetics research, which examines how genes are activated or silenced over time.
According to the statement, the project reached a significant breakthrough in summer 2025 when researchers reprogrammed skin cells from both boys into induced pluripotent stem cells (iPSCs). These lab-created stem cells can be developed into multiple types of human tissue, including brain cells, which allows researchers to study how trisomy 21 affects development and gene expression without invasive procedures. Unlike embryonic stem cells, iPSCs do not require the destruction of human embryos. The foundation said that in 2025, five independent research teams requested BioJeL resources to generate trisomy 21 iPSCs.
The twins’ mother, Elisabeth, said in the statement that the family chose to participate in the research to help further the world’s understanding of Down syndrome. She learned seven months into her pregnancy that Christian would be born with the condition.
“At first, it was a shock; I was mostly afraid that Christian would grow up in a society where differences are often unwelcome,” she said. “In reality, since his birth, he has been cherished by everyone.”
“Participating in the research project felt natural to us: we are happy to help advance the knowledge of trisomy 21,” she added, according to the release. “The doctors gave them two stuffed hummingbirds, which they are still very attached to. We are very proud of them."
The Foundation was established in 1996 to continue the work of Dr. Jerome Lejeune, the Catholic French geneticist who co-discovered the chromosomal cause of Down syndrome in 1958. His cause for canonization is currently open in the Church, and in 2021, he was declared Venerable. According to the release, the foundation pursues three primary goals: research on genetic intelligence disorders; medical care for individuals, especially those with Down syndrome; and advocacy for the life and dignity of those with disabilities from conception to natural death.