SALT LAKE CITY — He was born in New York on April 6, weighing almost exactly 7 pounds.
To his parents — a Jordanian couple who had suffered through several miscarriages and the death of two previous children from a mitochondrial disease inherited from the mother — he was nothing short of a miracle.
To the scientific community, he was a source of controversy — the first person in the world to be born using a technique that combines DNA from three adults.
The doctor who shepherded the first so-called "three-parent baby" into the world, Dr. John Zhang of New Hope Fertility Clinic, offered new details about the case at the annual American Society for Reproductive Medicine conference in Salt Lake City on Wednesday, adding to the first report by New Scientist in September.
"They are very brave," Zhang said of the Jordanian couple. "And they wanted to have a healthy baby after 10 years of nonstop trying."
The baby is 6 months old, healthy and will undergo a full medical exam soon, according to Zhang.
While science isn't a race, he added, "in a sense, it is a race for the family to find a cure, to find hope."
But Zhang has drawn criticism from bioethicists and scientists who say there is not enough evidence to know that the technique is safe for humans.
University of Utah medical ethics chief Dr. Jeffrey Botkin sat on a national panel of scientists gathered by the Food and Drug Administration earlier this year to weigh the ethics of "three-parent babies" — a term that many scientists say is misleading.
Botkin said he was "disappointed" in how Zhang conducted the case, including performing the procedure in the clinic's Mexico branch.
"It's hard to know what ethical standards were adhered to in the conduct of this work," Botkin said, adding that Zhang "sort of leapfrogged over several stages of scientific inquiry to go directly to delivering a baby."
Congress has banned the FDA from funding such work, meaning research on mitochondrial transfer technology is effectively on hold in the U.S.
The technique is supposed to prevent moms from passing on grave mitochondrial diseases to their children.
Mitochondria, which contain tiny amounts of their own DNA, are the powerhouse of the cell. They live outside of the nucleus, where the vast majority of a person's DNA is stored.
The mother in this case has a rare mitochondrial disease that led to the death of two previous children, one at age 6 and another at 8 months, according to the New York Times.
In Mexico, Zhang and his team removed the nucleus from the mother's egg and transferred it to the egg of a woman with healthy mitochondria. They then fertilized the hybrid egg with the father’s sperm.
Another method that involves the destruction of the mother’s embryo has raised concern in religious circles. That's not the technique Zhang used, nor did the devout Muslim couple want it, according to New Scientist.
Botkin and the bioethics panel concluded in February that it is "ethically permissible” to conduct clinical investigations of the technology in humans under certain conditions, but not until proven safe in animals and embryos.
One concern is that the technique does not replace all of the mother's defective mitochondrial DNA. As the baby grows up, the remaining defective DNA can become concentrated in certain organs or tissues, Botkin said, leading to complications.
"We think much more research had to be done at the animal level and the embryo level before it was ready for trying in real, live babies," Botkin said.
At the news conference, Zhang said the baby had 5 percent faulty mitochondria remaining. He also said the couple was properly counseled about the risks and alternatives of the procedure.
The couple — who have been patients of Zhang’s since 2011 — delayed for two years before deciding they wanted to proceed, according to Zhang. He said he was surprised to see the couple had kept detailed notes and drawings from past consultations, a sign they were serious about the procedure and its risks.
"(Leigh's syndrome) is a terrible, terrible disease," Zhang said. "We really feel we have the responsibility to advance this science to help this family."
Asked about the moral considerations of altering a baby's genetic makeup, Zhang pointed out that organ transplants and in vitro fertilization were once considered to be unethical.
It took "many, many years of responsible debate" for scientists and the public to accept those technologies, Zhang said.
More couples have since approached him wanting to undergo the same procedure, but the clinic has not pursued any more cases, he said.
"Practically, we need to take a vacation," Zhang said. "We are all really tired."