A technique to make “three-parent babies” was voted into law by the British Parliament in February 2015, but it wasn’t a “three-parent” baby born in the UK that made an ethical splash heard around the world — it was a baby boy born to a Jordanian couple treated in Mexico by a team of U.S. doctors. This procedure, called mitochondrial replacement therapy, is not legal in the U.S., so Dr. John Zhang and his team at the New Hope Fertility Center in New York City traveled to Mexico to treat the Jordanian woman.

The woman, identified as Ibtisam Shaban, has Leigh syndrome, which is a fatal disease affecting the developing nervous system, reported the New Scientist. The genes for Leigh syndrome are in the mitochondrial DNA of the mother. While Shaban did not exhibit symptoms of Leigh syndrome, she lost her first two children to the disease at ages six and eight months.

The procedure used to produce the baby, Abrahim Hassan, is surrounded by a flurry of ethical questions. In his case, Dr. Zhang removed the nucleus (which houses the majority of a person’s DNA) and placed it in the “shell” of a donor’s egg containing healthy mitochondria DNA. Another technique is to fertilize both the mother’s egg and the donor egg with the father’s sperm, then replace the donor’s nucleus with the mother’s. This technique destroys one embryo. While the mitochondrial transfer procedure is being hailed as a great accomplishment for those who have or are treating mitochondrial diseases, it also raises several serious ethical questions.

Altering the Germ Line

A child with mitochondrial DNA therapy will have DNA from three people, hence the term “three-parent babies.” Since mitochondrial DNA is passed from mother to child, females with three parents will permanently alter the “germ line” by passing the altered DNA to their children and so on. Dr Trevor Stammers, Program Director in Bioethics and Medical Law at St. Mary’s University, said, “Even if these babies are born they will have to be monitored all their lives, and their children will have to be as well. We do not yet know the interaction between the mitochondria and nuclear DNA. To say that it is the same as changing a battery is facile. It’s an extremely complex thing.”

Playing God

Some have charged that experimenting with DNA is “playing God,” and producing “genetically-modified” humans. “These regulations would authorize the crossing of a rubicon for the first time,” said British MP Fiona Bruce who chairs the All Party Parliamentary Pro-Life Group. “It would authorize germ line therapy… to alter the genes of an individual. This is something defined by the EU Charter of Fundamental Rights as effectively constituting eugenics.”

Only Boys Allowed

At this time, the procedure is only recommended to produce male embryos, since mitochondrial diseases are passed down through females. According to Science News, the Institute of Medicine in the United States determined “it would be ethical to produce male embryos using the technique,” but as of this year federal laws still prohibit the method. This means that female embryos would be destroyed in search of a male who would not pass on mitochondrial diseases to future generations.

Risk of Crossing Ethical Boundaries

British MP Jacob Rees Mogg said once the lines have been crossed, there’s no going back. “I think the difficulty is that it starts a process which is very hard to see where it stops,” he said. “Once the germ line is changed at one point you decide that isn’t allowable in other cases … there is a very clear boundary that babies cannot be genetically altered. And once you have decided that they can you have done something very profound.” Bruce concurs, “We … have approved a technique and what that technique could be used for in the future who knows,” she said. “We’re opening a Pandora’s box.”

The concerns around what amounts to having two mothers could present a problem in the future as child custody battles grow increasingly complicated, even as same-sex couples fight for custody of a child who biologically belongs to only one of them. Others worry that the legalizing of this technique will lead to creating “designer babies” on demand. While scientists may not be able to select a preferred eye color or hair color now, selecting embryos based on sex is already being done. Selecting other desired characteristics is only a matter of time. Once the laws are in place to perform mitochondrial DNA transfers in the U.S., the question of designer babies will be a nonissue.

Genetic Abnormalities

Perhaps one of the most alarming findings has to do with the very real possibility of genetic abnormalities for the three-parent babies. “There are numerous serious risks associated with this technology,” said Dr. Paul Knoepfler, Associate Professor at the University of California, Davis. “These include most notably the possibility that developmentally disabled or deceased babies will be produced. Aberrations could lead to developmental defects in babies or also manifest in later life as increased rates of aging [or] cancer.”

Dr. Knoepfler’s concerns are hardly unreasonable. In the early 1990s, embryologists in the U.S. performed a similar technique involving DNA from three people and the results were unsuccessful. The babies who were born later developed genetic disorders, including two infants born with a missing X chromosome and two who later had serious developmental disorders. The practice was banned after the problems were discovered.

Even with the mitochondrial DNA therapy there are no guarantees that the baby will be born without the mitochondrial disease the parents were hoping to avoid. Scientists are aware of mitochondrial carryover during nuclear transfer, also known as Genetic Drift — that is, the mitochondrial DNA of the mother carrying the disease could still carryover to the created embryo and eventually take over anyway, as reported in the journal Cell Stem Cell. Professor Mary Herbert of Newcastle University commented that “we don’t know what it means for development, but it’s alerted us to the fact that we really need to work hard to get as close to zero carry-over as we can.”

Following the UK’s legalization of the procedure, MEPs wrote to Prime Minister David Cameron, calling the practice “unethical.” In an open letter, the group warned Cameron that EU law prohibited genetic alterations that will carry on to the next generation. “Your proposals violate the fundamental standards of human dignity and integrity of the person,” they wrote. “Modification of the genome is unethical and cannot be permitted.” The Center for Genetics and Society (CGS) said it was “a historic mistake” and warned the technique “will turn children into biological experiments.”

CGS added, “… [T]hey will result in children with DNA from three different people in every cell of their bodies, which will impact a large range of traits in unknowable ways, and introduce genetic changes that will be passed down to future generations through the female line.”