The U.S. Food and Drug Administration held public hearings on February 25 and 26 to consider whether to permit scientists to begin human testing of a new method of assisted reproduction that would prevent the transmission of certain rare diseases and perhaps address some causes of female infertility. At issue is the safety of the technique, as well as its ethical implications.

What is it? The technology aims to prevent the transmission of certain rare, inherited diseases caused by defects in the DNA of mitochondria—structures within cells that convert the energy from food into a form that the cells can use. These defects, which are inherited only from mother to child, can cause loss of muscle coordination, visual and/or hearing problems, mental retardation, and other problems mainly of the brain, heart, at muscles.

To prevent transmission of mitochondrial diseases, scientists have developed assisted reproductive techniques that are similar to IVF, but involve an additional step. They create an embryo with the nuclear DNA (which contains most of the genetic information) from the prospective mother and father and the mitochondrial DNA from a donor without mitochondrial defects. Because the technology uses genetic material from three people, it is sometimes called “three-parent” reproduction.

Why is it controversial?  There are many points of controversy. The FDA hearings focused on safety questions:

1. What is known about the possible risks of the technology for the women involved (the mother-to-be and the mitochondrial DNA donor) and for any resulting children? It has been suggested that the technology itself might cause problematic genetic or epigenetic changes in the embryo or otherwise damage it, and that the DNA from the three parties might be incompatible.
2. Can clinical trials be designed to assess these risks?

These safety questions also contain ethical dilemmas. How do we balance trade-offs between different values– in this case, for example, the benefit of enabling women with defects in their mitochondrial DNA to have a genetically related child against the possible risk  that a child created this way might be harmed by the technology itself?

Other ethical concerns go beyond safety and risk. For one thing, unlike other human assisted reproduction technologies, mitochondrial DNA replacement would alter the germline, meaning that the mitochondrial DNA would be passed on by daughters to subsequent generations. Some people are opposed to this kind of genetic alteration, believing that it oversteps the proper role of humans in procreation and, indeed, evolution. Critics are also concerned that this technology could open the door to producing “designer babies”—children who are not simply free of severe genetic diseases, but are genetically selected for traits such as eye color or intelligence.

News in context: An earlier version of this technology was used in the U.S. about a decade ago, resulting in the birth of more than a dozen babies. But it ceased after the FDA ruled that it was a type of gene therapy and required further animal studies before it would consider an application to test the technology in humans. Now that animal studies have been undertaken, researchers have asked for FDA approval to conduct clinical trials. The safety and ethics of this technology have been discussed in other countries. In the United Kingdom, for example, the Human Fertilization and Embryology Authority concluded that clinical trials could take place provided they included long- term monitoring of children’s health.

“Real ‘designer babies’—whose embryos are custom built to meet the specifications of prospective parents—are still very much a science fiction fantasy (or, nightmare),” says Josephine Johnston, a research scholar at The Hastings Center who studies ethical issues in human assisted reproduction and genetics. “But the core concern raised by the term —that we are moving toward a new eugenics in which children are valued and ranked based on their genes and prospective parents feel pressure to use genetic technology to create the ‘best’ babies—is real and present, not only in the technology discussed by the FDA last week, but also in the current expansion of prenatal testing to include an ever-wider array of genetic traits.”

For more information, read “Stirring the Simmering ‘Designer Baby’ Pot,” a commentary in Science by Thomas H. Murray, President Emeritus. (Scroll down to “Recent Publications.”)