Start talking about 3-parent babies and thoughts may turn to science fiction. But, the technology to create a so-called 3-parent baby has been available since the 1990s; it just hasn’t been put to use much, or studied. That’s about to change, as the technology has been revived and refined.
The updated technique, called mitochondrial replacement therapy, is being used in conjunction with In vitro fertilization (IVF), both as a way of avoiding some genetic diseases, and a method for ensuring IVF implantation success. The results for the latter haven’t been promising. However, with little tracking or longterm studies, the repercussions for babies born through this technology are unknown.
Do 3-Parent Babies Truly Have 3 Parents?
Through technology, a 3-parent baby has the DNA of a third person (another woman) added through IVF.
Originally, Dr. Jacques Cohen came up with a cytoplasm transfer in the late 1990s. The procedure used the cytoplasm (the material inside a cell, excluding the nucleus) of a donor egg injected into the host egg, and then fertilized. It produced a zygote that had mitochondrial DNA from the donor and nuclear DNA from the host parents.
According to Nu Sci Mag, “Dr. Jacques Cohen reported in his book, Human Preimplantation Embryo Selection, the creation of 17 babies by this procedure, of which one was miscarried, and another was aborted.”
The other 15 babies, unfortunately, weren’t tracked to learn the longterm implications of the DNA mix.
“When the FDA [Food and Drug Administration] shut down the practice of cytoplasm transfer in 2001, labeling it ‘a biological product’ and therefore within their domain, the clinic of Dr. Cohen lost the funding and support to pursue follow-up studies on the 15 other chimeras,” Nu Sci reported.
So, while these babies don’t exactly have three parents, they do have extra DNA from an additional party besides their host parents. Living things that contain such “extra,” genetically distinct DNA are known by another name: chimeras.
Chimeras Aren’t Just Made in Labs
Chimeras do also occur naturally. A form of chimerism termed tetragametic occasionally (the American Journal of Medical Genetics estimates as many as 8% of fraternal twins have this) occurs when non-identical twins share a blood supply before birth. It can also occur with “vanishing twin syndrome,” in which one baby is born, but has cells from its now vanished sibling.
Another type of chimerism can happen when a patient receives a blood marrow transplant, then produces blood cells with DNA different from their original DNA. And, mothers often carry cells from the babies they carried, even years after their children are born.
Because chimeras are rare, they remain relatively unstudied. Chimeras born through mitochondrial replacement therapy are even rarer. The implications, both for the health of the baby and the genetic load down the germline, remain mysterious.
Mitochondrial Replacement Therapy Might Not Help Implantation
One of the justifications for implementing this new, improved fertility technology is to help implantation. Many women undergoing IVF endure two or more expensive and harrowing cycles of it. Ensuring implantation on the first try is a laudable goal.
A new study out of Ukraine suggests it doesn’t work so well. There are only two clinics worldwide performing the 3-parent procedure (it’s currently banned in the US), and the study results, presented at a meeting of the American Society of Reproductive Medicine in Philadelphia, showed only one in 109 procedures led to a baby.
One Zero Medium reported that US experts are negative on the 3-parent baby efficacy for implantation.
Dr. David Keefe, an obstetrician-gynecologist at NYU Langone Health, told One Zero Medium the results are evidence that faulty mitochondria are not to blame for the quality of a woman’s eggs or infertility. “They basically point out that it doesn’t work.”
Keefe suggests that tried-and-true options, like egg donation and surrogacy, are still the best bets if traditional IVF doesn’t work.
Avoiding Genetic Diseases
The real justification for the procedure might be trying to avoid genetic diseases by adding different DNA into the equation. A baby born through what some US doctors term mitochondrial donation (the procedure was performed in Mexico) was born free of a familial disease called Leigh Syndrome, which always leads to the death of the infant. The family had already lost two children and had suffered four miscarriages because of the disorder.
“The result is a baby with 0.1% of their DNA from the donor (mitochondrial DNA) and all the genetic code for things like hair and eye colour from the mother and father,” the BBC reported.
Unfortunately, the parents also refused to have their baby tracked. This is problematic, because very little is known about the future health consequences of the procedure.
Mitochondria might be powerful, but they’re also involved in metabolic, immune, neural, and psychiatric function. Earlier this year, researchers published a paper showing that mitochondrial DNA is closely tied to the DNA in the nucleus, meaning it might not be possible to use just any egg donor. A mismatch could cause health problems for the child later in life, Keefe told One Zero Medium.
A recent article in Nature pointed out that scientists, because of lack of tracking and very low sample sizes in existing research, are still in the dark about the impact on babies born from a 3-parent situation.
“Scientists don’t know what amount of diseased mitochondria would cause noticeable symptoms, or even disease, in a child created using genetic material from two women,” Nature reported. “But studies in mice have shown that mixtures of mitochondria can result in neurological disorders or metabolic conditions.”