In a first, a baby was born thanks to a controversial new technique employed by US scientists to include DNA from three parents in the embryo, said a report by AFP on Tuesday.
The baby boy was born five months ago in Mexico to Jordanian parents, and is healthy and doing well, said the report in New Scientist magazine. The boy's mother carried genes for a disorder known as Leigh Syndrome, a fatal nervous system disorder which she had passed on to her two previous children who both died of the disease. She had also suffered four miscarriages.
The genes for this disease are carried in the mitochondria, organelles that provide energy to the cell. Mitochondria carry exactly 37 genes passed down from the mother through the egg and are separate from the majority of our DNA that reside in the nucleus of the cell. Mutation in this mitochondrial DNA may not cause negative health effects for the mother but could cause mild or severe disorders for the child.
The woman, whose identity was withheld by the New Scientist, and her husband sought the help of John Zhang, a doctor from the New Hope Fertility Centre in New York City to have a baby that would be genetically related to them but would not carry the inherited disease. The United States has not approved any three-parent method for fertility purposes, so Dr Zhang went to Mexico where he was quoted by New Scientist as saying "there are no rules".
Dr Zhang has been working on a procedure to combat this disease, called the 'three-parent technique'.
One method that has been approved in the United Kingdom, called pronuclear transfer, was deemed unacceptable to the couple because it would involve the destruction of two embryos, said the report. Since the mother carried the genes for the disease in her mitochondria, or DNA that is passed down from the maternal side, Dr Zhang used her nuclear DNA and combined it with mitochondria from an egg donor, in a technique known as spindle nuclear transfer.
"He removed the nucleus from one of the mother's eggs and inserted it into a donor egg that had had its own nucleus removed," the report said.
"The resulting egg — with nuclear DNA from the mother and mitochondrial DNA from a donor — was then fertilized with the father's sperm."
Professor Sian Harding of London's Imperial College, who had reviewed the ethics of the pronuclear transfer method, said that Dr Zhang used an ethical approach by avoiding the destruction of embryos and by using a male embryo, so the child wouldn't pass on any inherited mitochondrial mutations, in the New Scientist exclusive.
Safety is still a concern as versions of the 'three-parent technique' applied earlier in the 1990s resulted in some of the babies wens on to develop genetic disorders and the technique was banned.
The problem may have arisen from the babies having mitochondria from two sources.
An abstract describing the research has been published in the journal Fertility and Sterility, but outside experts said much more remains to be understood about the research. Many are skeptical about the study and concerned about the health of the future health of the boy.
"As this technology is controversial and a world first, I think the investigators should have submitted a manuscript for full peer review instead of announcing these outcomes in this manner," said Justin St John, professor and Director of the Centre for Genetic Diseases at Monash University. Another outside expert, David Clancy, a lecturer at Lancaster University, recalled that experiments in monkeys have shown that maternal mitochondrial DNA can expand from low levels to significantly higher levels, "which would allow disease to again be transmitted, so we must expect the possibility in humans."
In a CNN report, an assistant professor at the University of Alberta School of Public Health, Lori P Knowles, called it 'reproductive tourism'- to go out of a system to create the safest and scientifically reproducible way forward. Another professor said that it is regrettable that it is taking place in countries that are distant to serious ethical and technical aspects of scientific procedures which mean it is going to be difficult to use the conclusions of this study in an organised data collection.
Further, she pointed out that the fact that four out of five embryos were nonviable, which itself suggests that the technique is not infallible.
"There's no guarantee the defective mutation might not accumulate within the baby boy and eventually lead to disease. "Which is the whole reason you're supposed to go slowly... and not jump right into creating babies", she said.
"We know that the procedure is not perfect," said Dr Clancy, who explained that in 2015, a published study showed "that tissue-specific expansion of mutated mitochondrial DNA during development can occur and so could cause disease if levels are high enough."
He suggested that a healthy baby might eventually develop a disease.
Zhang and his team are expected to describe their method at the American Society for Reproductive Medicine meeting in Salt Lake City, Utah, next month.
With inputs from AFP