Scientists in China used a new form of gene-editing technique CRISPR to correct a mutation in human embryos that causes Marfan syndrome, STAT reports.
The study results, published in Molecular Therapy Aug. 13, mark the first time CRISPR has been used in viable embryos created through in-vitro fertilization, a standard fertility clinic technique.
Researchers created embryos using an egg from a healthy woman and sperm from a man with Marfan syndrome, a genetic connective-tissue disorder caused by a mutation in the gene for the protein fibrillin on chromosome 15. After 16 to 18 hours, they injected some of the embryos with a newer and reputedly more precise form of CRISPR, called base editing.
Base editing changes a single DNA nucleotide — for example, it edits "C" to "T" or "G" to "A." By contrast, standard CRISPR breaks a DNA molecule, which repairs itself with a multi-letter repair gene supplied by the technology. Base editing reduces the risk of unintended genetic alterations that could arise from the "double-stranded breaks" in DNA molecules, according to STAT.
The researchers allowed the embryos to grow in the lab for another two days after injecting them with the CRISPR base editor, at which point they assessed the embryos for mutations.
The 18 embryos included in the study were corrected for Marfan syndrome. However, two exhibited unintended DNA changes: one had an unwanted edit from "C" to "T" and another had an unwanted edit from "G" to "A."
"All mutants were edited," Dr. Xingxu Huang, one of the lead study authors and a researcher at ShanghaiTech University in China, told STAT.
The researchers did not transplant the edited embryos to surrogate mothers.
"Overall, this pilot study provided proof of concept, and opened the potential of base editing-based gene therapy," Dr. Huang said. "Nevertheless, there is still a long way to go to use it in IVF clinics."