By FIONA MACRAE

Last updated at 08:18 16 August 2007

The prospect of holding back the years with a simple injection could be closer than we think.

Scientists have taken a step towards developing a treatment that could erase the health problems associated with ageing.

While their breakthrough relates to rogue genes behind two rare genetic diseases, the approach they used could one day be harnessed to slow down the ageing process - creating an "elixir of life".

The research focuses on mitochondria, sausage-shaped "powerhouses" in every cell of the body except red blood cells.

They turn the food we eat into energy that can be used by the heart, muscles, brain and other parts of the body.

Research has suggested their deterioration is an important cause of ageing, according to a report in New Scientist magazine.

About one in 5,000 children and adults are at risk of developing a mitochondrial disease, which include disorders of the nervous system and blindness.

One unique feature of mitochondria is that they have their own DNA, known as mitochondrial DNA, which is inherited from the mother only.

Defects in this mitochondrial DNA are blamed for a range of rare genetic diseases, including some forms of diabetes, blindness and heart problems.

They have also been linked to ageing - suggesting that fixing the flaws could slow down the onset of old age.

However, all attempts to fix flaws by inserting healthy DNA into mitochondria - a technique known as gene therapy - have failed, with the fresh genes stubbornly staying outside the powerhouses.

Now, by labelling the functional genes with an "address code" - which

effectively tells them where to go - French scientists have succeeded in smuggling them inside the mitochondria.

Once there, the pair of genes repaired the damage behind a rare form of blindness and a muscle wasting disease, says the New Scientist report.

In time, the same approach could be used to create injections of genes that will erase flaws thought to be linked to the ageing process.

However, while this might slow down ageing, it would not halt it completely, as mitochondria are just one of many factors involved in the ageing process.

Professor Patrick Chinnery, a leading British expert on mitochondrial disorders, said: 'It is not a panacea but, if successful, it might potentially correct part of this ageassociated damage to mitochondria which might be important in slowing down ageing.

"What they are doing sounds potentially a very clever idea.

"There is no treatment for these diseases, so any advance is clearly of great interest."

The researchers, from Marie Curie University in Paris, now plan to move their experiments from cells to rats, with human treatments the ultimate aim.

There are, however, many hurdles to be crossed. For instance, researchers need to be confident that genes act as billed and do not disrupt other vital processes.

They also need to work out how to get them to the right parts of the body without causing harmful side effects to other tissues.

Gene therapy offers hope of new treatments for a raft of illnesses, from cancer to Parkinson's disease.

In a recent trial reported in the Lancet, injections of genes into the brain significantly helped relieve the symptoms of Parkinson's disease.

Tremors and rigidity were reduced by up to 65 per cent, with no ill effects.