Pronuclear Transfer: How Families Have 3-Parent Babies

Named for the Latin term for "in a glass," in-vitro fertilization refers to the fact that an embryo is conceived outside of the body, which is called "in viro" in Latin. There are over 6.5 million babies that have been born with this technology, enough to say that IVF is common and mainstream despite being a controversial—and in some cases illegal—practice.

A new form of IVF, however, has been developed that gives scientists the ability to create one embryo from three different DNA sources.

The process is called pronuclear transfer and like the traditional IVF, it is also a controversial practice.

How Pronuclear Transfer Works

Typically, IVF has worked using straightforward science: one egg and one sperm sample. Donor eggs, donor sperm, or even a surrogate have meant that while the exact biological relation to the eventual family can be complicated, the actual process of IVF is not: scientists take one egg and fertilize it by inserting one sperm.

Pronuclear transfer, however, gives scientists the ability to create one embryo from three different DNA sources. The process was developed to help parents who have mitochondrial dysfunction, or defects in their DNA, conceive a healthy child that is also biologically connected to them. This type of IVF has often been dubbed "three parent IVF."

Essentially, scientists "swap out" the faulty strand or strands of DNA for healthier DNA. A mother's faulty DNA will be swapped with a healthy donor's DNA, making the egg a mixture of the two, and then the sperm is used to fertilize the egg.

The Benefits of Three Parent-IVF

Although exact numbers are not known, it's estimated that around 1 in 400,000 children have mitochondrial dysfunction, so it's relatively rare, but for those that do this can be a life-altering procedure.

For the parents choosing this procedure, three-parent IVF gives them the chance to be biologically connected to their baby while also reducing the risk of passing on a genetic disease.

The Risks Of Three-Parent IVF

Three-parent IVF is controversial because if the embryo that is produced is a girl, the genetic mutation can then be passed on to her own future children, if she has any. If the embryo is a boy the genetic mutation will not be passed on.

Initial research on three-parent IVF showed that it may also increase the resulting child's long-term chances of cancer and death.

There has also been some concern about the ethics of three-parent IVF, in that lawmakers and doctors have wondered if it would cause parents to be tempted to "design" babies that more closely fit their ideals. One doctor compared the process to creating genetically modified humans.

Much of the controversy boils down to your personal decision. If three-parent IVF becomes widespread, it would be up to you and your partner to get educated, discuss your options, and weigh the pros and cons.

The World's First Three Parent Babies

Using the pronuclear transfer, the world's first three parent baby girl has been born to a mother and father in Ukraine. CNN reported that in Ukraine, although doctors are aware of the potential risks and ethical considerations of having a baby girl born with the modified DNA, there are no specific regulations banning the procedure either.

In this case, the resulting male embryo just wasn't healthy enough, so a decision was made to proceed with the IVF transfer with the female embryo.

The reason the baby girl has gotten so much attention is because in this situation, the baby's mother did not have any known mitochondrial dysfunction that would warrant this procedure being necessary. Instead, the mother's own eggs could not be used on their own, so she requested that her DNA be inserted into a donor's egg so that she could be biologically related to the baby. 

Other three-parent babies have been born using different types of mixed-DNA techniques, although the U.S. has pretty strict regulations about using the procedure until doctors can agree on the ethics of it.

This family's example, though, opens up the floor to a new question in the front of IVF technology: Should parents be allowed to mix their own DNA into a donor egg, even if there is no medical reason to It's an interesting question and one that science will be trying to quickly answer.

Sources:

Amato, P., Tachibana, M., Sparman, M., & Mitalipov, S. (2014). Three-Parent IVF: Gene Replacement for the Prevention of Inherited Mitochondrial DiseasesFertility and Sterility101(1), 31–35.

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