New Results
, Jimin Kim, Julie Sung, Chanju Jung, Marcos Iuri Roos Kulmann, Melisa Isado, Hong-Su Jang, Meng Li, Sakshi Bhatele, Michelle Kappy, Shuangyi Xu, Gue-Ho Hwang, Jia Xu, Diego Marin, Jae-Sun Woo, View ORCID ProfileSangsu Bae, Nathan Treff, View ORCID ProfileDieter Egli
doi: https://doi.org/10.64898/2026.05.30.728989
ABSTRACT
Cas9-based tools enable the introduction of genetic lesions to investigate DNA repair outcomes and edit the genome at disease-relevant loci. DNA double-strand breaks (DSBs) induced by CRISPR/Cas9 result in frequent aneuploidy and large deletions, revealing a repair deficiency in early human embryos and limiting the clinical application of this technology. Here we evaluated the DNA repair outcomes of DNA nicks and mismatches introduced using base editors in human embryos at two targets, PCSK9 and HBG. Editing was efficient and, unlike Cas9-induced DSBs, did not result in either chromosomal abnormalities or large deletions. Small insertions or deletions after base editing were rare, and off-target activity was dependent on the guide RNA. Delivering the base editor as a protein at fertilization or at the pronuclear stage allowed normal development to the blastocyst stage and the derivation of edited stem cell lines. In stark contrast, introduction of the editor as RNA resulted in early embryo arrest. Our results demonstrated that, unlike DSBs, DNA nicks and mismatches are efficiently repaired in human embryos, allowing specific on-target changes without genotoxic consequences.
Competing Interest Statement
N.T., J.X., and D.M. are shareholders and/or employees of Genomic Prediction, Inc., a company providing chromosomal and SNP analysis for clinical purposes.
Funder Information Declared
IOCB Tech Foundation, Prague, CZ
New York Stem Cell Foundation, New York, US
Korean Fund for Regenerative Medicine, Seoul, KR
Genomic Prediction, New Brunswick, US
Copyright
The copyright holder for this preprint is the author/funder, who has granted bioRxiv a license to display the preprint in perpetuity. All rights reserved. No reuse allowed without permission.