Gene cure trials for blood-clot disorder

Doctors are preparing to run the first British clinical trial of a radical treatment for haemophilia, the blood- clotting disorder inherited by one in every 5,000 babies.

Doctors are preparing to run the first British clinical trial of a radical treatment for haemophilia, the blood- clotting disorder inherited by one in every 5,000 babies.

The trial will involve injecting volunteers with a genetically engineered version of the common cold virus containing a human blood-clotting gene. If the experiment works, patients will probably need only one injection every year rather than the three injections of blood-clotting agents they now receive each week to prevent uncontrolled bleeding.

Haemophilia, one of the first diseases to be shown to have a genetic cause, is seen as an important test of whether gene therapy can cure inherited diseases. Gene therapy has had only limited success, such as in treating rare disorders of the immune system.

Scientists from the Royal Free Hospital in London have had talks with the Government's gene therapy advisory committee, which regulates genetic experiments on patients. The trial could begin soon after they receive regulatory approval

The experiment will be based on a trial in the United States in which eight men with haemophilia are being injected with a virus that carries the corrected gene into the cells of the body, where it begins orchestrating the production of a protein factor that triggers the formation of blood clots.

Katherine High, a haematologist at the Children's Hospital of Philadelphia who is running the trial, had to suspend it last year after she detected viral genes in the semen of one of the volunteers. This raised fears that the gene therapy might result in the alteration of genes within sperm, risking the passing on of a genetic alteration of children. This would constitute "germline gene therapy", which is banned in both Britain and the United States.

Further research showed that the viral genes had not penetrated the sperm cells and that the virus was eventually cleared from the semen. The American Food and Drug Administration has therefore allowed the trial to continue, raising the prospect of a similar experiment in Britain.

Christine Lee, a professor of haemophilia and the director of the haemophilia centre at the Royal Free, said trials were expected, but when they would start was not clear. The formal proposal to the government committee was not finished, she said. "My guess is that certainly in the next five years we'll be participating in trials but I feel a little conservative about the time it will take for it to become mainstream treatment," Professor Lee said. "If someone has mild haemophilia, I don't think you're going to use gene therapy because the only time they're going to need treatment is when they have an operation."

Professor Lee said there were ethical difficulties with introducing a new treatment when existing therapies worked so well. People had to be told they were being used in an experiment rather than treated. Gene therapy, however, would have many advantages if it worked, she said. "It's a fantastic model for other inherited conditions."