Study identifies pitfall for correcting mutations in human embryos with CRISPR

October 29, 2020

In a paper published today in the journal Cell, scientists describe unexpected, undesirable outcomes after editing genes in human embryos with CRISPR, a genomic editing system.

The study, the most detailed analysis to date of CRISPR in human embryos, shows that applying CRISPR to repair a blindness-causing gene early in the development of a human embryo often eliminates an entire chromosome or a large section of it.

"Our study shows that CRISPR/Cas9 is not yet ready for clinical use to correct mutations at this stage of human development," says the study's senior author Dieter Egli, assistant professor of developmental cell biology in the Department of Pediatrics at Columbia University Vagelos College of Physicians and Surgeons.

CRISPR in human embryos

The genome editing system called CRISPR/Cas9 has revolutionized molecular biology in recent years, and its discoverers were honored with this year's Nobel Prize in chemistry. The system allows scientists to make precise changes in the genomes of cultured cells, living tissues, and animal embryos.

The first use of CRISPR in human embryos was reported in 2015. Just a few years later in 2018, He Jiankui claimed to have performed the procedure in a pair of twins, eliciting a firestorm of condemnation from scientists and government officials worldwide.

CRISPR can lead to chromosomal abnormalities

In the new paper, Egli and his colleagues tested CRISPR/Cas9 genome editing's effects on early-stage human embryos carrying a mutation in a gene called EYS (eyes shut homolog), which causes hereditary blindness.

"We know from previous studies in differentiated human cells and in mice that a break in the DNA results in mostly two outcomes: precise repair or small local changes. At the EYS gene, these changes can yield a functional gene, though it is not a perfect repair," says Michael Zuccaro, a PhD candidate at Columbia University Vagelos College of Physicians and Surgeons and co-lead author of the paper.

When Zuccaro, Egli and their colleagues looked at the entire genomes of the modified embryos in this study, they identified another outcome. "We learned that in human embryonic cells, a single break in the DNA can result a third outcome, the loss of an entire chromosome or sometimes a large segment of that chromosome, and this loss of the chromosome is very frequent," says Zuccaro.

In 2017, a study reported the successful correction of a heart disease-causing mutation in normal human embryos using CRISPR. Comprehensive data from the new study offer a different interpretation of these results: instead of being corrected, the chromosome carrying the mutation may have been lost altogether.

"If our results had been known two years ago, I doubt that anyone would have gone ahead with an attempt to use CRISPR to edit a gene in a human embryo in the clinic," Egli says. "Our hope is that these cautionary findings should discourage premature clinical application of this important technology, but can also guide responsible research to achieve its ultimate safe and effective use."
More Information

The study was published Oct. 29 in Cell, in a paper titled, "Allele-specific chromosome removal after Cas9 cleavage in human embryos."

Other authors: Michael V. Zuccaro (Columbia University Irving Medical Center), Jia Xu (Genomic Prediction Inc., New Brunswick, NJ), Carl Mitchell (CUIMC), Diego Marin (Genomic Prediction Inc.), Raymond Zimmerman (Genomic Prediction Inc.), Bhavini Rana (Genomic Prediction Inc. and Rutgers University), Everett Weinstein (CUIMC), Rebeca T. King (CUIMC), Katherine L. Palmerola (CUIMC), Morgan E. Smith (CUIMC), Stephen H. Tsang (CUIMC), Robin Goland (CUIMC), Maria Jasin (Memorial Sloan Kettering Cancer Center), Rogerio Lobo (CUIMC), and Nathan Treff (Genomic Prediction Inc. and Rutgers).

The U.S. government bans the use of federal funding to conduct research on human embryos, but the researchers were able to secure private funding from the New York Stem Cell Foundation and the Russell Berrie Foundation Program in Cellular Therapies to conduct the research.

Jia Xu, Raymond Zimmerman, Bhavini Rana, Diego Marin, and Nathan Treff are employees or shareholders of Genomic Prediction. Stephen Tsang was a consultant for SPARK Therapeutics and has grants from Abeona Therapeutics. Dieter Egli is a member of the Cell Advisory Board.

Columbia University Irving Medical Center

Related Chromosome Articles from Brightsurf:

The bull Y chromosome has evolved to bully its way into gametes
In a new study, published Nov. 18 in the journal Genome Research, scientists in the lab of Whitehead Institute Member David Page present the first ever full, high-resolution sequence of the Y chromosome of a Hereford bull.

Evolution of the Y chromosome in great apes deciphered
New analysis of the DNA sequence of the male-specific Y chromosomes from all living species of the great ape family helps to clarify our understanding of how this enigmatic chromosome evolved.

The male Y chromosome does more than we thought
While the Y chromosome's role was believed to be limited to the functions of the sexual organs, an University of Montreal's scientist has shown that it impacts the functions of other organs as well.

The birth of a male sex chromosome in Atlantic herring
The evolution of sex chromosomes is of crucial importance in biology as it stabilises the mechanism underlying sex determination and usually results in an equal sex ratio.

Why the 'wimpy' Y chromosome hasn't evolved out of existence
The Y chromosome has shrunken drastically over 200 million years of evolution.

Novel insight into chromosome 21 and its effect on Down syndrome
A UCL-led research team has, for the first time, identified specific regions of chromosome 21, which cause memory and decision-making problems in mice with Down syndrome, a finding that provides valuable new insight into the condition in humans.

Breakthrough in sex-chromosome regulation
Researchers at Karolinska Institutet in Sweden have uncovered a chromosome-wide mechanism that keeps the gene expression of sex chromosomes in balance in our cells.

B chromosome first -- mechanisms behind the drive of B chromosomes uncovered
B chromosomes are supernumerary chromosomes, which often are preferentially inherited and showcase an increased transmission rate.

Unveiling disease-causing genetic changes in chromosome 17
Extensive single Watson-Crick base pair mutations can occur in addition to duplication or deletion of an entire group of genes on chromosomal region 17p11.2.

What causes rats without a Y chromosome to become male?
A look at the brains of an endangered spiny rat off the coast of Japan by University of Missouri (MU) Bond Life Sciences Center scientist Cheryl Rosenfeld could illuminate the subtle genetic influences that stimulate a mammal's cells to develop as male versus female in the absence of a Y chromosome.

Read More: Chromosome News and Chromosome Current Events is a participant in the Amazon Services LLC Associates Program, an affiliate advertising program designed to provide a means for sites to earn advertising fees by advertising and linking to