DNA swap may be key to halting inherited illness

The British breakthrough opens up the possibility of avoiding mitochondrial disorders which can lead to early childhood death.

The diseases are caused by defective DNA in mitochondria – bean-shaped bodies in cells that act like batteries to generate energy.

Around one in 6,500 children in the UK is severely affected by the disorders, which can cause muscle weakness, blindness, heart and liver failure, diabetes and learning disabilities.

Mitochondria DNA is separate from that of the cell nucleus and contains far fewer genes. It is only passed from mothers to their children.

There are no treatments available which can cure mitochondrial diseases. Mothers with a family history of the disorders normally face the agonising choice of risking having an affected child or no child at all.

The new technique developed at the University of Newcastle raises the hope of ensuring a baby does not inherit malfunctioning mitochondrial DNA.

It involves transferring nuclear DNA inherited from a child's parents to a donor egg carrying its own, properly functioning, mitochondria.

"What we've done is like changing the battery on a laptop," said Professor Doug Turnbull, one of the study leaders. "The energy supply now works properly, but none of the information on the hard drive has been changed.

"A child born using this method would have correctly functioning mitochondria, but in every other respect would get all their genetic information from their father and mother."

Mitochondrial DNA only affects energy production, not all the characteristics that make a person a recognisable individual.

The mitochondria contain around 13 genes compared with an estimated 23,000 in the cell nucleus.

Members of the Newcastle team used a DNA-transfer technique similar to that employed in cloning.

A newly fertilised egg normally contains two "pronuclei" containing genetic material from the egg and sperm as well as mitochondrial DNA. Soon after fertilisation, the pronuclei fuse to form a single nucleus.

The scientists extracted the pronuclei from fertilised eggs in the laboratory, leaving behind the mitochondria.

They then implanted the pronuclei into fertilised donor eggs whose own pronuclei had been removed. The eggs were left with the transferred pronuclei plus working mitochondria from the women who donated them.

A total of 80 embryos were created using the technique. They were allowed to develop for six to eight days until they consisted of balls of around 100 cells called blastocysts.

In accordance with the research licence granted by the Human Fertility and Embryology Authority, they were then destroyed. But blastocysts are often used in IVF (In-Vitro Fertilisation) treatment to help women have children.

The research was published yesterday in the journal Nature.

Prof Turnbull said: "This is a very exciting development with immense potential to help families at risk from mitochondrial diseases.

"We have no way of curing these diseases at the moment, but this technique could allow us to prevent the diseases occurring in the first place."

The law prevents fertility treatment embodying such techniques but the Human Fertility and Embryology Act is flexible enough to allow Government permission for them in future.

Muscles require high levels of energy and are often most affected by mitochondrial disorders.

DEMENTIA 'NOT THE END OF LIFE' SAYS STUDY

People with dementia can have a good quality of life for a long time after diagnosis.

The study, from the Alzheimer's Society, examined the views of people living with dementia, asking what was important to them for a good quality of life.

The most important thing emerging from the study was maintaining relationships with family or friends and having someone to talk to.

A good environment, such as being at home, was the next most important thing followed by maintaining physical health.

Keeping a sense of humour came next, followed by having the ability to communicate with people and keeping a sense of personal identity.

The ability to keep up activities that have long been enjoyed came next, followed by the ability to still go to church or practise a religion.

The report said: "The ability to lead a fulfilled life doesn't stop on diagnosis. A good quality of life can be maintained."

Author Sir Terry Pratchett who has a rare form of dementia said: "Dementia is undoubtedly a cruel and debilitating condition. However a diagnosis does not strip a person of their identity. That person still has a voice and they deserve to be heard."