Three Parent Embryos: Exciting Development, Or Cause For Concern?


Scientists are exploring the possibility of creating human embryos with the DNA of three different parents. The purpose is to prevent heritable mitochondrial diseases that are incurable and often fatal. About 4000 children per year are born with genetic defects that affect mitochondria. Researchers have taken advantage of the fact that mitochondrial DNA is not part of the human genome, but is invariably passed from mother to child via the mitochondria that exist inside the ovum.

If a woman with a mitochondrial disease has children, she will pass on the DNA of these defective mitochondria. Researchers are exploring the possibility of removing the nucleus of an unfertilized ovum and inserting it into a donor ovum, sans nucleus, that came from a woman without a mitochondrial disease. The resulting egg would contain the human genomic DNA of the mother with a mitochondrial disorder, but the mitochondrial DNA of another mother without this disorder. The technique was successfully pioneered using rhesus monkeys in 2009, who are all raising healthy offspring.

More recently, the technique was used on human eggs to determine if this is a viable option for human would-be parents to consider. The nucleus was transferred from one ovum to another prior to fertilization, in a process known as spindle transfer. While the experiment produced normal, healthy blastocysts, over half of them developed abnormally. These abnormal blastocysts failed to discard the chromosomes normally removed at fertilization, and therefore contained an extra set of chromosomes. The problem was unexpected as it did not happen when working with rhesus monkey oocytes.

To circumvent this problem, another research team tried transferring the nucleus after fertilization to avoid the problem of cells failing to discard extra chromosomes during fertilization. This technique is called pronuclear transfer.

It is not currently legal for researchers to move from these preliminary studies to clinical trials in the United States and United Kingdom. However, the United Kingdom is reviewing the safety and efficacy of these techniques to assess the possibility of allowing for clinical trials.

Critics of these techniques are concerned that this research will lead to “designer babies” which are genetically modified to have specific traits. It is important to understand that the transfer of the DNA from one cell to another does not manipulate the genomic DNA at all, and to do so would be a much more complicated process. Other than mitochondrial defects, these hypothetical offspring would have all of the genetic traits inherited from two parents only.

Pro-life critics claim that this research is immoral because the fertilized eggs are “people” being genetically manipulated in a laboratory. Like with stem cell research, some people object to the use of any cell in a laboratory setting that could theoretically be developed into a human being. These critics would also oppose current in vitro fertilization techniques that allow infertile couples and homosexual couples to have children of their own. This moral objection has no scientific basis, so it cannot be dismissed by proving the safety and efficacy of the procedure.

There is no need to fear the onslaught of designer babies of the future, as this technology is far beyond the techniques being pioneered to prevent heritable mitochondrial diseases from passing to the next generation.

Gavid Gardner is a science blogger and tech extraordinaire. He contributed this post on behalf of -the U.K.’s top store for research chemicals.

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