The human embryos used in the research were created using eggs collected from healthy women and sperm from a man carrying a DNA error. Thus some of the embryos carried the DNA error, and some were “healthy”.Led by Hong Ma of Oregon Health and Science University, the researchers then used the gene-editing technology known as CRISPR in the embryos to try to correct the error, which causes catastrophic genetic heart disease in adults.In more than half of the embryos, the DNA mutation was replaced with “healthy” DNA, and these embryos appeared to grow normally to the blastocyst stage (the point at which they would normally be transferred back into the woman’s uterus during the IVF process – in this study, the blastocysts were destroyed during analysis).

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