Technique to limit transfer of faulty DNA to embryos

accreditation

Scientists recently unveiled an improved method of transferring DNA between human egg cells, a technique that aims to create embryos free of their mother's genetic defects.

An array of disorders

Refinements to an existing method known as "pronuclear transfer", sometimes called three-person IVF, greatly reduced the amount of faulty, disease-causing DNA in the lab-produced embryos, they reported in the journal Nature.

The method involves extracting healthy DNA of the mother and father from the nucleus of a fertilised egg. Each egg cell also contains a different type of DNA residing in tiny cell structures called mitochondria.

Sometimes the mitochondrial DNA undergoes mutations which can be transmitted to offspring and can cause an array of disorders.

Read: Some people defy their 'genetic destiny' and sidestep disease

The nuclear DNA is transferred into a donated egg cell with healthy mitochondrial DNA from which the nucleus has been removed.

"(W)e are optimistic that the technique we have developed will offer affected women the possibility of reducing the risk of transmitting mitochondrial DNA disease to their children," said study co-author Mary Herbert of the Wellcome Trust Centre for Mitochondrial Research in England.

Commentators said the study marked significant progress towards a safer form of in-vitro fertilisation (IVF) for women who carry disease-causing mitochondrial mutations.

Estimates vary widely, but about one in 5,000 children is thought to be born with these mutations which can affect the muscles, eye, brain or heart.

There is no effective treatment.

Mitochondria are tiny structures inside our cells which turn sugar and oxygen into energy. They are often referred to as the powerhouses or batteries of our cells.

No guarantee

Mitochondria have their own DNA, which is separate from the DNA within the cell nucleus.

Sometimes, mutations in these genetic codes can cause the mitochondria to malfunction, resulting in organ failure and even death.

Unlike nuclear DNA, which is transferred to offspring by the mother and father combined, mitochondrial DNA is inherited from the mother alone.

Last year, Britain became the first country in the world to legalise pronuclear transfer for women with mitochondrial disorders.

The new study, using over 500 eggs from 64 donor women, showed that small tweaks to the existing procedure can reduce the risk of mutant mitochondrial DNA transferral.

Read: UK plans world's first '3-parent' IVF babies

It worked best to perform the procedure on the day of the egg's fertilisation, not later, the scientists found.

And it was better to freeze the egg of the patient, rather than that of the donor.

Refining the techniques

The embryos, which were not allowed to develop, contained less than two percent of the mutated mitochondrial DNA in the original egg, the authors found. This is below the five-percent threshold considered safe.

The study was an important step, said commentators, but the two-percent level was still no guarantee against disease.

According to Marni Falk of The Children's Hospital of Philadelphia's human genetics division, "There is the chance that even small levels of mutant mtDNA (mitochondrial DNA) can become unpredictably enriched in the developing person over time."

Added Herbert: "Our ongoing research is focused on refining the techniques to further reduce the risk of transmitting disease."

The results of the study will be presented to an expert panel of Britain's fertility treatment regulator, the Human Fertilisation and Embryology Authority, which must decide whether to issue the first licence to a clinic.

Read more:

Scientists question ethics of 'designer babies'

Britain's new gene technology gets the go-ahead

Germany approves genetic testing

We live in a world where facts and fiction get blurred
In times of uncertainty you need journalism you can trust. For 14 free days, you can have access to a world of in-depth analyses, investigative journalism, top opinions and a range of features. Journalism strengthens democracy. Invest in the future today. Thereafter you will be billed R75 per month. You can cancel anytime and if you cancel within 14 days you won't be billed. 
Subscribe to News24
Voting Booth
Zama zama crackdown: What are your thoughts on West Village residents taking the law into their own hands?
Please select an option Oops! Something went wrong, please try again later.
Results
Authorities should bring in the army already
10% - 1819 votes
Illegal miners can't be scapegoated for all crime
50% - 8690 votes
What else did we expect without no proper policing
36% - 6215 votes
Vigilante groups are also part of the problem
3% - 604 votes
Vote
Rand - Dollar
16.42
-1.4%
Rand - Pound
19.86
-1.1%
Rand - Euro
16.74
-0.8%
Rand - Aus dollar
11.54
-0.2%
Rand - Yen
0.12
-1.7%
Gold
1,774.64
-1.5%
Silver
20.16
-3.2%
Palladium
2,152.00
-3.4%
Platinum
934.50
-3.3%
Brent Crude
98.15
-1.5%
Top 40
64,055
+0.1%
All Share
70,770
+0.1%
Resource 10
63,403
-1.0%
Industrial 25
86,990
+0.5%
Financial 15
16,141
+0.5%
All JSE data delayed by at least 15 minutes Iress logo
Editorial feedback and complaints

Contact the public editor with feedback for our journalists, complaints, queries or suggestions about articles on News24.

LEARN MORE