How a third parent’s DNA can prevent hereditary diseases like cancer in a baby

Science continues to make great strides in the 21st Century.

In the UK, eight children have thus far been born using the DNA of three people, a method known as mitochondria donation treatment (MDT), researchers say.

This conception method allows women not to pass down genetic defects – thus creating healthier babies.

But what is MDT? And how can a third parent’s DNA prevent diseases in a baby?

Let’s take a closer look:

What is MDT?

MDT is a fertilisation technique developed by researchers at the UK’s Newcastle Fertility Centre, the Newcastle upon Tyne Hospitals NHS Foundation Trust and a specialist service within the National Health Service.

It was designed in order to stop mothers from passing on such unhealthy mitochondrial DNA to their babies.

Mitochondria are special organisms in cells. They perform several important functions in the human body including breaking down food molecules and powering the cells.

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They are present in almost every cell the human body and known as the “powerhouse of the human body”. Their DNA, known as mitochondrial DNA, is inherited from the mother

However, mutations in the mitochondrial DNA can prove devastating to human beings. They have been blamed for causing diseases such as cancer, neurodegenerative disorders, heart diseases, epilepsy and stroke.

Around 1 in 5,000 people are estimated to have a genetic mitochondrial disease.  In Britain, where this technique has been pioneered, that number is 1 in 200.

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Some babies are also born with incurable mitochondrial disease. In such instances, their bodies cannot produce enough energy. These babies are usually severely disabled and only live for a few days.

Fortunately, just a handful of such babies are born every year.  In the UK, for example, only five babies have been born with this disorder.

The names of the babies and their families have been kept under wraps to protect their identities.

The UK in 2015 became the first country in the world to pass a law regulating such procedures.

This came despite the experts from the Zoological Society of London pointing out that faulty mitochondrial DNA had been transplanted during the procedure in half of animal studies conducted.

The US Food and Drug Administration at the time had also declared the process unsafe.

Under UK law, every woman choosing to undergo the procedure must be okayed by its fertility regulator.

The regulator must determine that the family has no other choice to avoid passing on genetic illnesses.

How does it work?

The technique works by combining the sperm and the egg from a man and a woman with a second egg from the donor.

Essentially, the genetic material from the first fertilised egg is injected into the second fertilised egg.

This embryo is then implanted in the mother’s womb.

While the baby gets most of the genetic material from its parents (99.9 per cent), it also gets the added benefit of having the healthy mitochondrial DNA from the donor.

The ‘three-parent’ moniker is thus slightly misleading, experts say.

The UK witnessed its first such baby conceived by MDT treatment in 2023.

“Mitochondrial donation treatment offers families with severe inherited mitochondrial illness the possibility of a healthy child,” the UK fertility regulator said at the time.

How has it helped?

Nearly two dozen families have been treated at the Newcastle Fertility Centre.

The families of the eight babies born via this MDT treatment have had rare but fatal mitochondrial disorders for generations.

This, according to two papers published in The New England Journal of Medicine.

The children range from under six months to over two years old. They comprise four boys and four girls including a pair of identical twins.

All the children appear healthy and happy, though researchers say their health needs to be tracked in the long-term.

“Mitochondrial disease can be devastating for the family. It can be tragic,” Doug Turnbull, a professor of neurology who is one of the Newcastle University researchers told NPR. “This is an important breakthrough — a big step forward.”

“I think everybody knows I’m a natural pessimist, so it’s a relief”, Turnbull told The Telegraph.

Bobby McFarlane, professor of Paediatric Mitochondrial Medicine at Newcastle University, told The Telegraph, “All the children are well and they are continuing to meet their developmental milestones. While longer term follow-up of children born following mitochondrial donation is of paramount importance, these early results are very encouraging. Seeing the joy and relief these children have brought to their parents is such a privilege”.

Many are ecstatic about the results – none more than the parents.

“After years of uncertainty this treatment gave us hope - and then it gave us our baby,” one parent told the B_BC._ “We look at them now, full of life and possibility, and we’re overwhelmed with gratitude.”

“Thanks to this incredible advancement and the support we received, our little family is complete”, another added. “The emotional burden of mitochondrial disease has been lifted, and in its place is hope, joy, and deep gratitude.”

“I think this is a landmark advance. It is pioneering work,” Dietrich Egli, an associate professor of developmental cell biology at Columbia University, told NPR. Egli has called for the Food and Drug Administration to allow such research to be done in the US. “It is extraordinary — no question about it.”

Others have called the development a ““scientific tour-de-force”.

However, critics of this treatment point to the fact that its long-term effects on the health and safety of children born this way remain unknown.

They say couples have other ways they can avoid passing down diseases such as egg donations and screening tests.

They also warn that the day when couples choose to have ‘designer babies’ is not far off.

With inputs from agencies