By James Gallagher Health reporter, BBC News Just one injection could be enough to mean people with haemophilia B no longer need medication, according to an early study in the UK and the US.
Six patients were given a virus that infects the body with the blueprints needed to produce blood-clotting proteins. Four of them could then stop taking their drugs.
Doctors said the gene therapy was "potentially life-changing".
Other researchers have described it as a "truly a landmark study."
