The UK government has pledged to closely monitor gene therapy treatments after a controversial case in France.
BBC News Online examines the technique and explains why it is controversial.
What is gene therapy?
Gene therapy is a way of treating disease by either replacing damaged or abnormal genes with normal ones or by providing new genetic instructions to help fight disease.
Instead of giving a patient a drug to treat or control the symptoms of the disorder, in gene therapy doctors attempt to correct the underlying problem by introducing healthy copies of the damaged or missing genes into some of the patient's cells.
These therapeutic genes are transferred into the patient in a number of ways.
These include attaching it to a non-threatening virus or another similar carrier "vector" and injecting it into the body.
It can also involve "naked" DNA being delivered into cells.
Studies have suggested that the treatment could help patients with a range of conditions and diseases from infertility to cancer.
Why is it controversial?
The treatment is controversial because there has been little evidence - until recently - that it works.
The technique has been shown to work in animals but there has been only limited success in humans.
Gene therapy has been used to successfully treat patients with haemophilia.
It has also been used to cure a British infant of "bubbly boy" disease, which meant he had no immune system.
However, authorities in the United States have found that hundreds of experiments have failed and have caused a number of deaths.
Now authorities in France have suspended trials after a child developed leukaemia after undergoing treatment.
What might have caused the cancer?
It is possible that the virus carrying the new gene is inserted close to another gene that plays a role in triggering leukaemia.
This disruption may in some way stimulate the cancer-causing gene to become active.
Why is the French decision important?
The decision by French authorities is important not least because it could be a major setback for the entire gene therapy programme.
Doctors in Paris were trying to cure eight children with "bubble boy" disease - the largest trial of its kind.
The decision is also significant given that the treatment has proved successful in other patients.
There is no evidence yet that the technique caused leukaemia but authorities are investigating whether there is a connection.
What is the UK government's position?
UK authorities are keeping the situation under review. The Medicines Controls Agency is to investigate events in France.
Members of the Department of Health's gene therapy advisory committee have also pledged to monitor trials closely.
However, they have decided against following the French example and suspending trials.
What is the future for gene therapy?
Doctors and scientists working in the field are confident that gene therapy could provide the key to curing a wide range of major diseases.
They, however, acknowledge that much more study is needed before the technique can be used extensively.
Authorities in the UK also remain confident that the technique will one day help many children and adults with incurable diseases.