Tears for the transhumanists

As noted in this story at Nature, gene editing by CRISPR on human embryos is still not a thing, basically because it's too clumsy a technique:

As well as addressing broader concerns about ethics and social justice, editing embryos would require a safe and effective genome-editing platform to minimize the chances of harm to the embryo, the resulting child and any descendants. Most research on genome editing in embryos, however, has been done using animal models such as mice, which might not accurately reflect what happens in human embryos. And, although potential genome-editing therapies have been widely studied in adult human cells, embryos might respond differently than adult cells to the DNA damage caused by some of the tools.

Only a handful of laboratories have directly tried to edit the genomes of human embryos using the popular editing system CRISPR–Cas9, and several of these presented concerning results at the summit.

The Cas9 enzyme works by breaking both strands of DNA at a site designated by a guiding piece of RNA. The cell then repairs the break, either by using an error-prone mechanism that stitches the two ends together but sometimes deletes or inserts a few DNA letters in the process, or by replacing the missing DNA with a sequence copied from a template provided by the researcher. DNA breaks created by Cas9 in embryos are usually repaired using the error-prone pathway, said Dietrich Egli, a stem-cell biologist at Columbia University in New York City, at the conference.

Egli and other researchers also reported on the consequences of the double-strand breaks made by Cas9. Developmental biologist Kathy Niakan, now at the University of Cambridge, UK, recounted that her lab found that some human embryos lost large regions of chromosomes when they were edited using CRISPR–Cas9¹. Shoukhrat Mitalipov, a reproductive biologist at Oregon Health & Science University in Portland, also said that his team had found large DNA deletions at the editing site in human embryos, and that these deletions might not be detected using standard tests².

“Can human embryos at this stage really tolerate this kind of intervention?” asked Dagan Wells, a reproductive geneticist at the University of Oxford, UK, who also reported concerning responses to DNA breaks in human embryos. About 40% of the embryos in one of his genome-editing studies failed to repair broken DNA. More than one-third of those embryos continued to develop, he said, resulting in the loss or gain of pieces of chromosomes in some cells. That could harm the health of the child if such embryos were allowed to develop further. “These results are really a warning,” he said.