Researchers have used a gene-editing tool to repair the segment of DNA that causes hypertrophic cardiomyopathy in human embryos, according to a study published in Nature.
Investigators from the Institute for Basic Science in South Korea used CRISPR-Cas9, a tool that has been shown to eliminate or replace pieces of DNA in specific genes. The experiments were conducted in the United States by researchers from the Oregon Health and Science University and followed all ethical guidelines. The procedure included donated healthy egg cells and the sperm of a man affected by hypertrophic cardiomyopathy.
CRISPR-Cas9 corrected the hypertrophic cardiomyopathy mutation in the DNA of the sperm by cutting the DNA near the position of the mutation. The cut was either repaired without the hypertrophic cardiomyopathy mutation, or it was repaired with unwanted insertions or deletions of a few base pairs near the cutting site.
CRISPR-Cas9 cut the DNA in the correct position in all of the tested embryos, and 72.4% of the embryos did not carry the hypertrophic cardiomyopathy mutation. The investigators noted that the human embryos have an alternative DNA repair system, where the cuts in the DNA coming from the sperm are repaired based on the DNA from the healthy egg. In the remaining 27.6% of embryos, this repair system introduced unwanted insertions or deletions near the cut.
Researchers from the Institute for Basic Science also performed an analysis to ensure that CRISPR-Cas9 would not cut any other sites of the human genome. Sequencing of the whole genome did not reveal any additional cuts.
“[Preimplantation genetic diagnosis] may be a viable option for heterozygous couples at risk of producing affected offspring,” the study authors concluded. “In cases when only one parent carries a heterozygous mutation, 50% of embryos should be mutant. In contrast, targeted gene correction can potentially rescue a substantial portion of mutant human embryos, thus increasing the number of embryos available for transfer.”
In an accompanying article, Nerges Winblad and Fredrik Lanner, from the Department of Clinical Science, Intervention and Technology at the Karolinska Institute in Stockholm, Sweden, note that it is promising that the embryonic genome integrity is maintained after CRISPR-Cas9 editing, but further studies will be needed to optimize this technology.
“These will have to confirm that the approach is safe in terms of criteria such as mosaicism, off-target editing and the detection of abnormalities in edited embryos before it can be used as a therapy for inherited diseases,” they wrote. “Nevertheless, this study is paving the way as part of investigations that might lead to CRISPR–Cas9 reaching the clinic in the future. Until then, embryo genetic testing during [in vitro fertilization] remains the standard way to prevent the transmission of inherited diseases in human embryos.
- Correction of a faulty gene in human embryos [press release]. EurekAlert. Published August 2, 2017. Accessed August 7, 2017.
- Ma H, Marti-Gutierrez N, Park SW, et al. Correction of a pathogenic gene mutation in human embryos. Nature. 2017 Aug 2. doi:10.1038/nature23305
- Winblad N, Lanner F. Biotechnology: At the heart of gene edits in human embryos. Nature. 2017 Aug 2. doi:10.1038/nature23533