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Thursday, 2 March, 2000, 13:10 GMT
Surprise gene therapy success
Haemophiliacs need tranfusions of blood clotting factors
Haemophiliacs need tranfusions of blood clotting factors
The long wait for success in gene therapy may be over, with promising results in two patients receiving treatment for haemophilia.


One patient had a 80% reduction in the need to administer factor IX

Dr Mark Kay
The experiment was only meant to show that the treatment was safe but it has allowed them to greatly reduce their standard treatment.

Doctors said the two men had shown evidence that their new genes were working several months after they were first injected.

Until now, gene therapy experiments have been heavily tarnished by failures and scandal.

Viral vector

Katherine High of the Children's Hospital of Philadelphia and Mark Kay of the Stanford University School of Medicine were working on a gene therapy treatment for haemophilia B, a bleeding disorder that affects about one in 50,000 males.

These patients have a defective gene for a protein known as factor IX which is important for helping the blood clot. Unless they get regular injections of factor IX, they can suffer from internal bleeding or other problems and die.

The doctors, working with a California-based company, Avigen, have been developing ways to carry a healthy version of the factor IX gene into the bodies of their patients. The aim is for the new gene to help them naturally produce enough of the protein to stay healthy.

Transfusions can be required several times a week
Transfusions can be required several times a week
They used a virus called an adeno-associated virus to carry the gene into their patients' bodies. Such viruses do not cause disease in humans but are very good at getting into cells, and are considered safer than other viruses used in gene therapy.

Three patients took part in a Phase I trial meant to show only that the approach was safe. The doctors said they never expected to see evidence that the gene therapy affected their patients' haemophilia.

But it did, according to their report in the journal Nature Genetics.

80% reduction

"One patient had a 50% reduction in the need to administer factor IX and the other had an 80% reduction," Dr Kay said.

What is also surprising is that the treatment leads patients to produce less than 1% of the normal level of factor IX, but that small amount is enough to be beneficial.

"It's just barely detectable," Dr Kay said. "But it is enough to help control their bleeding. I wouldn't say they don't have bleeding events - they just have reduced frequency."

Gene therapy has been under fire since the death last September of 18-year-old Jesse Gelsinger during an experiment. Since then, US federal regulators have found that some researchers have not been reporting "adverse events" as quickly as required.

Dr Kay said he hoped his study would help people realise that gene therapy is not always dangerous: "I hope that it makes people realise that all gene therapy is not based on the methods used in the Gelsinger case and that there are other strategies likely to be useful in the future."

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