'Matching' DNA could make for healthier 3-parent babies: study

Better matching the DNA of egg donors and recipient mothers-to-be may limit the risk of transferring disease-causing mutations to so-called three-parent babies, a study suggested Wednesday. While further work is needed, the study adds to the fast-growing field of in-vitro fertilisation for women with damaged mitochondrial DNA (mtDNA) -- the type inherited solely from our mothers. An egg donor -- the third parent along with the couple who go on to give birth to and raise a baby -- should be selected whose mtDNA is genetically closely related to that of the recipient mother, the authors wrote in the journal Nature. Every cell in the human body holds about 23,000 genes, almost all of them in the nucleus -- so-called nuclear DNA. But 37 genes reside in tiny structures called mitochondria, which are the batteries of cells, turning sugar and oxygen into energy. Nuclear DNA is transfer to offspring by both the father and mother, but mitochondrial DNA is inherited from the mother alone. Some women have damaged mtDNA, which if transferred to their children can cause a variety of debilitating and untreatable diseases. Women with mitochondrial mutations can have healthy children via in-vitro fertilisation, using a technique called mitochondrial replacement therapy. The nuclear DNA is taken from their own egg, and placed with the father's sperm into a different egg, its nucleus removed, from a donor with healthy mitochondria which is left intact. However, it sometimes happens in lab experiments that cells cultivated using this method revert to the mother's mutated mtDNA -- traces of which may have been carried over with her nuclear DNA. The latest study looked at ways of preventing this. Things were less likely to go wrong when the egg donor's mitochondrial DNA was "compatible" with that of the mother, it found. Mitochondrial DNA can be divided into groups known as haplotypes, each with a common genetic ancestor. "This research suggests that we're going to have the greatest success rates for producing an embryo free of disease-causing genetic mutations by making sure we are using the right combination of haplotypes," said the study's senior author Shoukhrat Mitalipov. Further work is needed to develop a DNA matching technique, even before clinical trials can start. Trials cannot be done in the United States, where most of the study authors are from, under a ban on mitochondrial replacement therapy. The first baby created using mitochondrial replacement was born in Mexico earlier this year. It was born from the same "spindle transfer" technique used in the latest study, which unlike the "pronuclear transfer" method does not entail the destruction of an embryo. Only Britain has so far authorised 'three-parent babies" for women with disease-causing mitochondria.