Eight children in the UK are the first to share DNA from three different parents.
The babies were conceived via IVF, using the egg and sperm from their parents, along with a second egg from a donor.
The scientific breakthrough has been achieved in order to save the children from inheriting mitochondrial disease, normally passed from mother to child.
Mitochondrial diseases are a group of genetic conditions that impact how mitochondria in your cells produce energy. If a person has mitochondrial disease, the body's cells will not be able to create enough energy.
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The condition can cause severe disability, and some babies may even pass away within days of birth.
In a huge feat for science, eight infants conceived through mitochondrial donation have now been born in the UK.
The babies were conceived using a technique that transfers the nucleus of a fertilised egg that has faulty mitochondria into the donor egg cell, which has a healthy mitochondria.
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“This is a landmark study on preventing mitochondrial disease,” says Dietrich Egli, a stem-cell scientist at Columbia University.
The procedure is known as three-person IVF due to the fact that each child will have DNA from their mother, father, and the DNA from the egg donor.
However, the amount of DNA inherited from the donor is tiny, around 0.1 percent.
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Two reports, published in the New England Journal of Medicine, revealed how 22 families have now gone through mitochondrial donation at the Newcastle Fertility Centre, which has led to four boys and four girls - two of which are twins - as well as another pregnancy.
"To see the relief and joy in the faces of the parents of these babies after such a long wait and fear of consequences, it's brilliant to be able to see these babies alive, thriving and developing normally," Professor Bobby McFarland, the director of the NHS Highly Specialised Service for Rare Mitochondrial Disorders told the BBC.
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The children are all developing normally and the eldest is over two years old.
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However, an important question from the breakthrough is whether any faulty mitochondria could be transferred into the healthy embryo.
In five of the cases, mitochondria was undetectable, while in the other three, it was detectable between five and 20 percent. However, this is still lower than the 80 percent threshold which is thought to cause disease.
“We’re cautiously optimistic about these results,” Robert McFarland, a paediatric neurologist at Newcastle University, said.
“To see babies born at the end of this is amazing, and to know there’s not going to be mitochondrial disease at the end of that.”
Lucy Devine