New Study Reveals Safety of Controversial 3-Parent Embryo Technique: ScienceAlert

When a baby is born with three biological parents in 2016, there were concerns about the ethics and safety of the procedure.

During the experimental procedure, the mother’s nuclear DNA was transplanted in a donor egg with its own nuclear DNA removed. Doctors then fertilized the donor egg with the transplanted nuclear DNA using the husband’s sperm.

This procedure was intended to prevent the child from inheriting a rare neurological condition called Leigh syndrome, which can be passed down through maternal mitochondria.

The worry was that the traces of maternal mitochondria extracted during the spindle transfer would multiply, creating health problems for the child.

spindle transfer involved extract the spindle-shaped set of chromosomes containing the mother’s nuclear DNA from an egg.

However, a study looking at the effect of this procedure on the genetics of individual cells five days after fertilization found that they were no different from a control group, suggesting that the procedure does not affect development. embryonic in its infancy.

The researchers used a single-cell triple omics sequencing method to examine the genome, DNA methylome and transcriptome to dozens of cells at the stage of blastocyst development.

“Our results suggest that spindle transfer appears to be generally safe for embryonic development, with a relatively minor delay in the DNA demethylation process at the blastocyst stage,” the authors explain. report.

“Mitochondrial replacement therapy is a controversial area”, said Study co-author Wei Shang, an obstetrician and gynecologist at Chinese PLA General Hospital in Beijing. “Through our research, we hope to provide a basis for the development of the technique.”

Dietrich Egli, a stem cell biologist at Columbia University, said Nature the study was “unique and fabulous” because of its high quality data.

“It’s the first [study] who performed such a comprehensive comparison of human embryos created by spindle transfer,” he said. said.

The location of the nucleus and mitochondria in a human cell. (Eranicle/Getty Images)

The first child conceived using donor mitochondria and the spindle transfer method in 2016 had no health problems seven months after birthbut the long-term effects are not yet known.

“Maternal mitochondria and nucleus coexist for a long time, so maybe the nucleus may prefer cells with maternal mitochondria,” said Min Jiang, a mitochondrial biologist at Westlake University in Hangzhou, China. said.

“So far, studies show that spindle transfer works. But the long-term health of children born with the therapy will need to be studied with clinical trials,” she said. said.

In the case of 2016, less than 5 percent of maternal mitochondrial DNA containing the pathological variant was transferred. Current techniques can reduce that to 2%.

The UK and Australian governments have legalized the donation of mitochondria to prevent serious hereditary genetic diseases. But it’s still banned in the United States and its legality is uncertain in China.

Leigh’s syndrome is one of the rare diseases caused by pathological variants in maternal mitochondria affecting up to 1 in 5,000 children.

Children with Leigh Syndrome do not survive beyond the age of two or three years. They lose their mental, movement and swallowing abilities, and experience difficulty breathing, vomiting, diarrhea and stunted growth.

Most of the DNA in human embryos comes from the nucleus inside the human egg and sperm. But the mitochondria, which are the powerhouses of the cell, also contain DNA. There are until 25,000 genes in the core and just 37 genes in the mitochondria.

Sperm contains mitochondrial DNA, but it is destroyed in the process of fertilizationand therefore only the mother’s mitochondria are left to replicate.

This article was published in PLOS Biology.

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